Chapter XXXII: Section V (4)

The character of the section established on _Danthonia Forskalii_ would chiefly consist in the very remarkable obliquity of the joints of the locusta, which is, indeed, so great, that after their separation each flower seems to have at the base an almost vertically descendent spur; and as the inferior extremity of the upper joint is produced beyond the lower, a short calcar actually exists before separation, and this calcar is equally manifest in the terminal rudiment of the locusta. The present, therefore, is a case of more remarkably oblique articulation in grasses than even that existing in _Holcus acicularis_ (Andropogon acicularis, _Retz_) which led to the formation of _Centrophorum_; a genus still admitted by Professor Sprengel[122], and respecting the structure of which a very singular explanation has been lately offered by M. Raspail[123]. In one respect, the two cases differ. In _Danthonia_ (_Centropodia_) _Forskalii_, the articulations being in the axis of the locusta or spicula, each flower appears to have this spur-like process; while in _Holcus_ (_Rhaphis_) _acicularis_, the joint being in the peduncle or branch of the racemus, the spur is common to three locustæ.

Dr. Fischer, in whose herbarium the specimen was observed which led to the formation of Centrophorum, will probably recollect the communication made to him on the subject of that plant, of which Dr. Trinius himself has since corrected the characters. He retains it, however, as a distinct genus, for which he has adopted the name Rhaphis, given to it by Loureiro, by whom it was originally proposed, on other, but not more satisfactory grounds.

TRIRAPHIS PUMILIO is the second plant of this family to be noticed. It is undescribed, and belongs to a genus of which the only two published species were found in the intratropical part of New Holland[124]. In several points of structure the African plant is very different from _T. pungens_, the first of these species; in some respects it approaches to _mollis_, the second species, especially in the inequality of its setæ or aristæ, but it differs from both in habit, and in having only one perfect flower in each locusta[125].

Of PENNISETUM DICHOTOMUM, (_Delile, Flore d’Egypte_, p. 15, tab. 8, f. 1.), which, in several different states, is in the collection, it is remarked by Dr. Oudney, that “it is a great annoyance to man and beast, from the prickly calyx (involucrum);” and by Major Denham, that from Aghedem to Woodie “it covered the surface of the country, and annoyed the travellers to misery;” he observes, also, that the seed is called _Kasheia_, and is eaten.

PANICUM TURGIDUM, (_Forsk. Arab._ p. 18; _Delile, Flore d’Egypte_, p. 19, tab. 19, f. 2.), is also one of the most common grasses from Tripoli to Bornou.

Of ACOTYLEDONES, the only plant in the collection is _Acrostichum velleum_, found on the Tarhona mountains. Mr. Ritchie’s herbarium contains, also, a single plant of the same family, namely _Grammitis Ceterach_.

The foregoing observations have extended much beyond the limits which the number and importance of the plants they relate to may seem to require. I still regret, however, that I cannot add a few remarks on such species as, although not in the herbarium, were observed, either indigenous or cultivated, in the countries visited by the mission, and for information respecting which I am indebted to Major Denham and Captain Clapperton. But it being determined no longer to delay the publication of the very interesting Narrative, to which the observations already made will form an Appendix, I am unable at present to enter on this part of my subject.

FOOTNOTES:

[Footnote 87: _Floræ Libycæ Specim._ p. 35.]

[Footnote 88: _Syst. Vegetab._ 2. p. 871.]

[Footnote 89: _Handb. tab._ 180.]

[Footnote 90:

SAVIGNYA.

Savignya. _De Cand. Syst._ 2. p. 283. Lunariæ sp. _Delile. Desvaux. Viviani._

CHAR. GEN. _Calyx_ basi æqualis; æstivatione valvata. _Silicula_ oblonga, septo conformi, valvis convexiusculis. _Semina_ biseriata imbricata marginata. _Cotyledones_ conduplicatæ.

Herba _annua, glabra_ (_quandoque pube rara simplici_). Folia _crassiuscula, inferiora obovata in petiolum attenuata grosse dentata, media sæpe incisa, superiora linearia_. Racemi _oppositifolii, ebracteati_. Flores _parvi erecti, petalis violaceis venis saturatioribus_. Siliculæ _racemosæ, divaricatæ, inferiores sæpius deflexæ_.

_Calyx_ erectus, æstivatione valvata, ipsis apicibus vix imbricatis. _Petala_ unguiculata, laminis obovatis sub æstivatione mutuo imbricatis. _Stamina_ distincta, edentula, singulum par longiorum _glandula_ subquadrata extus stipatum; breviora, quantum e speciminibus observare licuit, eglandulosa. _Ovarium_ brevissime pedicellatum, ovulis adscendentibus nec horizontalibus. _Stylus_ brevis. _Stigma_ capitatum vix bilobum. _Silicula_ breviter manifeste tamen stipitata, oblonga nunc oblongo-elliptica. _Valvulæ_ uninerviæ reticulato-venosæ. _Dissepimentum_ e lamellis duabus separabilibus uninerviis venis anastomozantibus obsoletis: areolis subtransversim angustato-linearibus, parietibus (tubulis) rectis subparallelis. _Funiculi_ horizontales, dimidio inferiore septo arcte adnato superiore libero.]

[Footnote 91: _Flor. Lib. Specim. p._ 34. _tab._ 16. _f._ 1.]

[Footnote 92:

KONIGA.

Konig. _Adans. fam._ 2. p. 420. Lobularia. _Desvaux in Journ. de Botan. appl._ 3. p. 172. Alyssi sp. _Hort. Kew. ed._ 2. vol. 4. p. 95. _De Cand. Syst. Nat._ 2. p. 318. Lunariæ sp. _Viv. Libyc._ p. 34. Farsetiæ sp. _Spreng. Syst. Veg._ 2. p. 871.

CHAR. GEN. _Calyx_ patens. _Petala_ integerrima. _Glandulæ_ hypogynæ 8! _Filamenta_ omnia edentula. _Silicula_ subovata, valvis planiusculis, loculis 1-polyspermis, funiculis basi septo (venoso, nervo deliquescenti,) adnatis. _Semina_ (sæpissime) marginata. _Cotyledones_ accumbentes.

Herbæ (_annuæ v. perennes_) _pube bipartita appressa incanæ_. Folia _integerrima sublinearia_. Racemi _terminales, nunc basi foliati_. Flores _albi_.

_Calyx_ basi subæqualis. _Petalorum_ laminæ dilatatæ. _Antheræ_ ovatæ. _Glandularum_ quatuor per paria filamenta longiora lateraliter adstantes; reliquæ quatuor abbreviatæ geminatim filamenta breviora stipantes. _Dissepimentum_, præter _areolas_ ultimas (laminæ duplicis) transversim lineares parietibus (tubulis) rectis subparallelis, _venis_ crebre anastomozantibus a _nervo_ descendenti e duobus arcte approximatis formato supra basin evanescenti in monospermis obsoleto ortis descendentibus. _Funiculi_ in dispermis polyspermisque in diversis loculis alterni.

OBS. Koniga ad Alyssinearum tribum _De Cand._ pertinens, hinc Alysso auctorum inde Farsetiæ accedit. Sed Alyssum, uti in Hort. Kew. et De Cand. Syst. Nat. constitutum sit, certe divisionem eget.

ALYSSUM _nob._ facile distinguendum sequentibus notis. Silicula subrotunda, disco convexo, limbo compresso, apice retuso, loculis dispermis, funiculis basi septo adnatis et post lapsum seminum persistentibus, supra liberis et cum iisdem deciduis, in diversis loculis oppositis, in eodem a styli basi equidistantibus: Petalis emarginatis: Filamentis omnibus nonnullisve appendiculatis in speciebus omnibus præter A. calycinum in quo filamenta filiformia simplicia sunt et glandularum loco setulæ quatuor filamenta nana æmulantes exstant.

Ad Alyssum sic constitutum et herbas plerumque annuas pube stellari foliisque integerrimis complectens pertinent A. campestre et calycinum _Linn._ strigosum _Russell._ minimum _Willd._ et strictum _ejusd._ a quo densiflorum _Desfont._ vix differt; fulvescens _Smith_, umbellatum _Desv._ rostratum _Stev._ micropetalum _Fisch._ hirsutum _Bieb._ aliasque species ineditas.]

[Footnote 93:

FARSETIA.

Farsetia. _Turra Farsetia_, p. 5. Farsetiæ sp. _Hort. Kew._ ed. 2. vol. 4. p. 69. _De Cand. Syst._ 2. p. 286.

CHAR. GEN. _Calyx_ clausus, basi vix bisaccatus. _Filamenta_ omnia edentula. _Antheræ_ lineares. _Silicula_ ovalis v. oblonga, sessilis, valvis planiusculis, loculis polyspermis (raro 1-2-spermis), funiculis liberis. _Dissepimentum_ uninerve, venosum. _Semina_ marginata. _Cotyledones_ accumbentes.

Herbæ _suffruticosæ ramosæ, pube bipartita appressa incanæ_. Folia _integerrima_. Racemi _subspicati_.

OBS. Dissepimentum in omnibus exemplaribus utriusque speciei a nobis visis completum, sed in F. ægyptiaca quandoque basi fenestratum, fide D. Desfontaines. (_Flor. Atlant._ 2. _tab._ 160.)

F. ægyptiaca species unica certa est, nam F. stylosa, cujus flores ignoti, ob stigmatis lobos patentes non absque hæsitatione ad hoc genus retuli.

FARSETIA? _stylosa_, ramosissima, siliculis oblongis polyspermis passimque brevè ovalibus 1-2-spermis, stylo diametrum transversum siliculæ subæquante, stigmatis lobis patentibus.

_Obs._ Exemplaria omnia foliis destituta, sed illorum cicatrices ni fallor obviæ.]

[Footnote 94: In a work published in 1810, the following passage, which has some relation to this subject, occurs. “Capsulas omnes pluriloculares e totidem thecis conferruminatas esse, diversas solum modis gradibusque variis cohæsionis et solubilitatis partium judico.”—(_Prodr. Flor. Nov. Holl._ 1. p. 558.) This opinion, however, respecting the formation of multilocular ovaria, might be held, without necessarily leading to the theory in question of the composition of the fruit in Cruciferæ, which I first distinctly stated in an Essay on Compositæ, read before the Linnean Society in February 1816, and printed in the 12th volume of their Transactions, published in 1818. In this volume (p. 89), I observe that “I consider the pistillum of all phænogamous plants to be formed on the same plan, of which a polyspermous legumen, or folliculus, whose seeds are disposed in a double series, may be taken as the type. A circular series of these pistilla disposed round an imaginary axis, and whose number corresponds with that of the calyx or corolla, enters into my notion of a flower complete in all its parts. But from this type, and number of pistilla, many deviations take place, arising either from the abstraction of part of the complete series of organs, from their confluence, or from both these causes united, with consequent abortions and obliterations of parts in almost every degree. According to this hypothesis, the ovarium of a syngenesious plant is composed of two confluent ovaria, a structure in some degree indicated externally by the division of the style, and internally by the two cords (previously described), which I consider as occupying the place of two parietal placentæ, each of these being made up of two confluent chordulæ, belonging to different parts of the compound organ.”

In endeavouring to support this hypothesis by referring to certain natural families, in which degradations, as I have termed them, are found, from the assumed perfect pistillum to a structure equally simple with that of Compositæ, and after noticing those occurring in Goodenoviæ, I add, “The natural order Cruciferæ exhibits also obliterations more obviously analogous to those assumed as taking place in syngenesious plants; namely, from a bilocular ovarium with two polyspermous parietal placentæ, which is the usual structure of the order, to that of Isatis, where a single ovulum is pendulous from the apex of the unilocular ovarium; and, lastly, in the genus Bocconia, in the original species of which (_B. frutescens_), the insertion of the single erect ovulum has the same relation to its parietal placentæ, as that of Compositæ has to its filiform cords, a second species (_B. cordata_) exists, in which these placentæ are polyspermous.”

From this quotation it is, I think, evident, that in 1818 I had published, in my Essay on Compositæ, the same opinion, relative to the structure of the pistillum of Cruciferæ, which has since been proposed, but without reference to that essay, by M. de Candolle, in the second volume of his “Systema Naturale;” and I am not aware that when the essay referred to appeared, a similar opinion had been advanced by M. de Candolle himself, or by any other author; either directly stated of this family in particular, or deducible from any general theory of the type or formation of the pistillum. I am persuaded, however, that neither M. de Candolle, when he published his Systema, nor M. Mirbel, who has very recently adverted to this subject, could have been acquainted with the passage above quoted. This, indeed, admits of a kind of proof; for if they had been aware of the concluding part of the quotation, the former author would probably not have supposed that all the species referred to Bocconia were monospermous, (_Syst. Nat._ 2. p. 89); nor the latter that they were all polyspermous. (_Mirbel in Ann. des Scien. Nat._ 6. p. 267). Respecting _Bocconia cordata_, though it is so closely allied to Bocconia as to afford an excellent argument in favour of the hypothesis in question, it is still sufficiently different, especially in its polyspermous ovarium, to constitute a distinct genus, to which I have given the name (MACLEAYA _cordata_) of my much valued friend, Alexander Macleay, Esq. Secretary to the Colony of New South Wales, whose merits as a general naturalist, a profound entomologist, and a practical botanist, are well known.]

[Footnote 95:

OUDNEYA.

CHAR. GEN. _Calyx_ clausus, basi bisaccatus. _Filamenta_ distincta, edentula. _Stigmata_ connata apicibus distinctis. _Siliqua_ sessilis linearis rostrata, valvis planis uninerviis, funiculis adnatis, septo avenio areolarum parietibus subparallelis. _Semina_ uniseriata. _Cotyledones_ accumbentes.

Suffrutex (O. Africana _nob._ Hesperis nitens, _Viv. lib. p._ 38. _tab._ 5. _f._ 3.) _glaberrimus, ramosus_. Folia _integerrima sessilia avenia, inferiora obovata, superiora sublinearia_. Racemi _terminales, ebracteati_. Flores _mediocris magnitudinis, petalorum laminis obovatis venosis_.

_Obs._ Oudneya ab Arabidi differt stigmatis forma, siliquæ rostro, et dissepimenti areolarum figura. Parrya ad quam genus nostrum accedit diversa est dissepimento binervi venoso! calyce haud clauso, siliquæ forma, et seminibus biseriatis testa corrugata.]

[Footnote 96: _Tuckey’s Congo_, p. 469.]

[Footnote 97:

MÆRUA.

Mærua. _Forsk. Arab._ p. 104. _Vahl symb._ 1. p. 36. _De Cand. Prodr._ 1. p. 254.

CHAR. GEN. _Calyx_ tubulosus: _limbo_ 4-partito, æstivatione simplici serie valvata: _corona_ faucis petaloidea. _Petala_ nulla. _Stipes genitalium_ elongatus. _Stamina_ numerosa. _Pericarpium_ (siliquiforme?) baccatum.

Frutices _inermes, pube, dum adsit, simplici_. Folia _simplicia coriacea_: _petiolo cum denticulo rami articulato_: stipulis _minutissimis setaceis_.

MÆRUA _rigida_, corymbis terminalibus paucifloris, foliis obovatis crassis rigidis aveniis nervo obsoleto, corona lacero-multipartita.

DESC. Frutex? _Rami_ stricti teretes tenuissime pubescentes. _Folia_ sparsa, obovata cum mucronulo brevissimo, plana semiunguicularia, utrinque pube tenuissima brevissima simplici, nervo obsoleto, venis fere inconspicuis. _Petioli_ lineam circiter longi. _Stipulæ_ laterales, setaceæ, petioli dimidio breviores, ramulo appressæ, post lapsum folii persistentes. _Ramuli floriferi_ sæpius laterales abbreviati, e foliis confertis floribusque corymboso-fasciculatis (3-6.), quorum exteriores folio subtensi; quandoque corymbus ramum terminat. _Pedunculi_ teretes, tenuissime pubescentes, ebracteati excepto foliolo florali dum adsit ejusque stipulis vix conspicuis. _Calyx_ infundibuliformis, extus tenuissime pubescens: _tubus_ subcylindraceus, 8-striatus striis elevatis æqualibus, intus lineis duabus prominulis subcarnosis, cum limbi laciniis alternantibus, altera crassiore: _limbus_ tubo paulo longior, 4-partitus laciniis æqualibus, ovatis acutiusculis, obsolete venosis, 5-nerviis, nervis extimis margini approximatis, e furcatione costarum quatuor tubi cum laciniis alternantium ortis; æstivatione simplici serie valvata marginibus tamen paulo inflexis. _Corona faucis_ monophylla, laciniis limbi multoties brevior, lacero-multipartita lacinulis subulatis inæqualibus. _Stipes genitalium_ liber, cylindraceus, glaber, altitudine tubi. _Stamina_: _Filamenta_ indeterminatim numerosa, viginti circiter, filiformia glabra, æstivatione contortuplicata. _Antheræ_ incumbentes, ovali-oblongæ obtusæ, basi semibifidæ, loculis parallelo-approximatis, intus longitudinaliter dehiscentibus, æstivatione erectæ. _Ovarium_ e centro filamentorum stipitatum, cylindraceum, glabrum, uniloculare placentis duabus parietalibus polyspermis. _Stylus_ nullus. _Stigma_ depresso-capitatum.

OBS. Species hæcce proxime accedit Mæruæ senegalensi _nob._ quæ vix pubescens et foliis venosis distincta; in multis quoque convenit, fide descriptionis Forskalii, cum Mærua uniflora _Vahl_, a nobis non visa. Mærua angolensis, _De Cand._ (in Museo Parisiensi visa) cui flores pariter corymbosi et corona lacero-multipartita, satis diversa est foliis ovalibus.]

[Footnote 98: _Annal. du Mus. d’Hist. Nat._ 18. _p._ 392.]

[Footnote 99: _Théor. Elem. ed._ 2. _p._ 244.]

[Footnote 100: _Collect. Bot. tab._ 22.]

[Footnote 101: _Sp. plant._ 2. _p._ 564.]

[Footnote 102: In Hooker’s _Flora Scotica_, p. 284.]

[Footnote 103:

PARKIA.

ORD. NAT. _Leguminosæ-Mimoseæ_: Cæsalpineis proximum genus.

CHAR. GEN. _Calyx_ tubulosus ore bilabiato (⅔); æstivatione imbricata! _Petala_ 5. subæqualia, supremo (paulo) latiore; æstivatione conniventi-imbricata. _Stamina_ decem, hypogyna, monadelpha. _Legumen_ polyspermum: _epicarpio_ bivalvi; _endocarpio_ in loculos monospermos sarcocarpio farinaceo tectos solubili.

Arbores (_Africanæ et Indiæ orientalis_) _inermes_. Folia _bipinnata, pinnis foliolisque multijugis_; stipulis _minutis_. Spicæ _axillares, pedunculatæ, clavatæ floribus inferioribus_ (_dimidii cylindracei racheos_) _sæpe masculis_.

PARKIA _Africana_, pinnis sub-20-jugis, pinnulis sub-30-jugis obtusis intervalla æquantibus, cicatricibus distinctis parallelis, glandula ad basin petioli, rachi communi eglandulosa, partialium jugis (2-3) summis glandula umbilicata.

Inga biglobosa, _Palis de Beauv. Flore d’Oware_, 2. p. 53. tab. 90. _Sabine in Hortic. Soc. Transact._ 5. p. 444. _De Cand. Prodr._ 2. p. 442.

Inga Senegalensis. _De Cand. Prodr._ 2. p. 442.

Mimosa taxifolia. _Pers. Syn._ 2. p. 266. n. 110.

Nitta. _Park’s First Journey_, p. 336-337.]

[Footnote 104: _Park’s Second Journey_, p. cxxiv. where it is stated to be an undescribed species of that genus. Soon after that Narrative appeared, on comparing Mr. Park’s specimen, which is in fruit only, with the figure published by Lamarck in his Illustrations (_tab._ 602. _f._ 4.), and with M. Poiret’s description (_Encyc. Meth. Botan._ 5. p. 728.), I referred it to that author’s _P. erinacea_, a name which is, I believe, adopted in the last edition of the Pharmacopœia of the London College. Dr. Hooker has since published a drawing of the same plant by the late Mr. Kummer, and considering it a new species, has called it Pterocarpus Senegalensis. (_Gray’s Trav. in Western Africa_, p. 395, tab. D.)]

[Footnote 105: _Tuckey’s Congo_, p. 430.]

[Footnote 106: _Memoires sur la Famille des Legumineuses_.]

[Footnote 107: _Flinders’s Voy. to Terra Austr._ 2. p. 542.]

[Footnote 108: _Flinders’s Austr._ 2, p. 559.]

[Footnote 109: _Prodr. Flor. Nov. Holl._ 1, p. 558.]

[Footnote 110: _Theor. elem. ed._ 2. p. 183.]

[Footnote 111: _Cæsalp. de Plantis_, p. 327. cap. xv. et p. 351. cap. liii.]

[Footnote 112: _De Cand. Legum._ p. 52.]

[Footnote 113: OXYSTELMA _Bornouense_, floribus racemosis, corollæ laciniis semiovatis, folliculis inflatis, foliis lanceolatis basi cordatis.

_Obs._—Inflorescentia et corolla omnino _O. esculenti_, a quo differt folliculis inflatis, et foliis omnibus basi cordatis.]

[Footnote 114: _Salt’s Voy. to Abyss. append._ p. lxiii.]

[Footnote 115: _Park’s First Journey_, p. 202 and 352.]

[Footnote 116: _Prod. Flor. Nov. Holl._ 1, p. 528.]

[Footnote 117: IPOMŒA _Clappertoni_, glaberrima repens, foliis sagittatis: lobis posticis acutiusculis integerrimis, pedunculis unifloris.]

[Footnote 118: _Colchicum_ (_Hermodactylus_) _Ritchii_, limbi laciniis basi intus bicristatis! fasciculo 2-multifloro, foliis linearibus.

_Obs._—Spathæ 2-8-floræ; limbi laciniæ vel lanceolatæ acutiusculæ vel oblongæ obtusæ; cristæ laciniarum omnium sæpe fimbriato-incisæ, exteriorum nunc integerrimæ. Ovula in singulis ovarii loculis biseriata, placentarum marginibus approximata; nec ut in C. autumnali quadriseriata.]

[Footnote 119: Botan. Magaz. 1028.]

[Footnote 120: The late celebrated M. Richard, in his excellent “Analyse du Fruit,” in pointing out the distinctions between a simple and compound pericarpium, produces that of Melanthaceæ as an example of the compound, in opposition to that of Commelineæ or of Junceæ, which, though equally multilocular, he considers as simple. A knowledge of the structure of Colchicum Monocaryum would, no doubt, have confirmed him in his opinion respecting Melanthaceæ.

It has always appeared to me surprising, that a carpologist so profound as M. Richard, and whose notions of the composition of true dissepiments, and even of the analogy in placentation between multilocular and unilocular pericarpia, were, in a great degree, equally correct and original, should never have arrived at the knowledge of the common type of the organ or simple pistillum, to which all fruits, whether unilocular or multilocular, were reducible; and that he should, in the instance now cited, have attempted to distinguish into simple and compound two modifications of the latter so manifestly analogous, and which differ from each other only in the degree of coalescence of their component parts.]

[Footnote 121: _Flinders’s Voy. to Terra Austr._ 2. p. 582.]

[Footnote 122: _Syst. Veg._ 1. p. 132.]

[Footnote 123: _Annal. des Scien. Nat._ 4. p. 425.]

[Footnote 124: _Prodr. Flor. Nov. Holl._ 1. p. 185.]

[Footnote 125: _Triraphis Pumilio_, panicula coarctata abbreviata, locusta glumam vix superante 3-4-flora: flosculo infimo hermaphrodito; reliquis neutris univalvibus.]

No. XXIII.

_Letter to Major Denham, on the Rock Specimens brought from Africa. By
Charles Konig, Esq. F.R.S._

_British Museum, Feb. 25th_, 1826.

My dear Sir,

I have great pleasure in transmitting to you, for whatever use you may think proper to make of it in the Appendix to your forthcoming work, the little I have to advance on the geological and a few other objects, that were collected by you, the late Dr. Oudney, and Captain Clapperton, on your journey through the great African desert, and are now deposited in the British Museum. It chiefly consists of the descriptive catalogue of a small series of rock specimens, originally drawn up by me without particular regard to their geognostic occurrence; to which I now prefix a few desultory remarks that occurred to me, when, with a view to its publication, I subjected that list to a second perusal. My materials are, indeed, very scanty; but their description may, nevertheless, (in conjunction with the observations dispersed in the body of the work, of which I have not been able to avail myself) lead some of your geological readers to more or less important results relative to the structure of the tract of country in which they were collected.

There are among the specimens I have examined none that might be referred to the primitive formations, except those gathered south and west of Kouka. The principal specimen of granite (No. 1.) brought by you from the Mandara mountains strongly resembles some of the fresh large-grained varieties of the same from the Fetish rocks in Congo. Those from Soudan, with feldspar, in its progress to kaolin, (No. 5.) betray the principal cause of the striking appearance of the granite mountains in that part of central Africa. The effects of atmospheric influence on that component, spreading chiefly in the direction of the natural rifts of the rock, are, in the Soudan mountains as well as in those of the Hartz, the Riesengebirge, and other European granitic districts, manifested partly by the immense and numberless blocks, wholly or partially detached, and confusedly piled up on the sides of the mountains, or strewed over the plains in fantastic groups; and partly by the almost total disintegration of the masses into gravel at the foot of the ridges. The former of these effects is illustrated by the sketch of a granite mountain in Soudan, which you were so good as to show me. There are a few other specimens of granite from Soudan; but they present no characters from which any useful information is likely to be derived; the less so, as they appear to be casual fragments, not found in situ. The mica slate (No. 9.), as Captain Clapperton informed me, occurs at the upper part of the ridges between Quarra and Zurma; and a ticket, accompanying a micaceous rock specimen, (No. 11.) from the same locality, as I suppose, states it to be “used for glazing earthen ware.”

These are all the specimens of primitive rocks. As to those of secondary and tertiary formations, which have been brought home, it will appear from the subjoined catalogue, (as, indeed, with regard to part of the kingdoms of Tripoli and Fezzan, has already been pointed out by Dr. Buckland), that they may be referred to three formations, viz. 1. to the fletz-trap or basaltic formation; 2. to a formation analogous to the Paris limestone, (calcaire grossier, grob-kalk); and 3. to some members of the secondary formation from the chalk to the alpine limestone inclusively.

The few specimens of the first mentioned of these formations are specified under Nos. 14 to 18. To the second I would refer the sandstone No. 26. with fragments of small univalve shells, not unlike a species of Paludina, and the plastic clay of Cano, of which, I suppose, are made the light pipe bowls, brought from thence; together with some other specimens of clay, and also some fragments of shells, apparently from the tertiary limestone, but the localities of which are not mentioned.

But by far the greater proportion of the specimens brought home by you belongs to that series of the secondary formations of which the variegated sandstone is the principal member. Subordinate to this is the ferruginous sandstone, (Nos. 47, &c.) with its beds of brown hydrous oxide, into which, as also into ochrey ironstone, (Nos. 84—90.) it appears to pass by gradual transition. The white sandstone, called quader-sandstein by most German geologists, and sandstone of Konigstein by Baron Humboldt, is not specified as such in the list; I am, however, inclined to think it is not entirely wanting in several parts of the tract you have traversed, especially to the southward of the boundary of Fezzan. I conclude it, from what you have mentioned to me of the picturesque and ruin-like appearance of many of the mountain ranges in those parts, which is peculiar to that sandstone; from the external character of some of the specimens, which, however, have no localities affixed to them; as also from the impressions of small bivalves on one or two of them. No stress is perhaps to be laid on the occurrence of fibrous limestone, which substance is known to be among the mineral contents of quader-sandstone at the foot of the Hartz, where this link of the fletz sandstone formation rests on the red marle sandstone, without the intervention of shell limestone, of which latter I have seen no specimens among those from North Africa.

More characteristic are the specimens of the variegated sandstone, properly speaking. The varieties, which, by their patches, stripes, and flamed delineations, are more particularly entitled to that denomination, are Nos. 31—36. The friable sandstone of Traghen (No. 23.) probably owes its green colour to oxide of nickel: the colouring matter seems chiefly to reside in the clay by which the grains are held together.

Particularly remarkable are those varieties of sandstone in which the cement is quartz, both with and without ferruginous admixture (Nos. 37—46). They are all (with the exception of a few of more loose texture, which belong to a tertiary formation) referable to the variegated sandstone series. In some of these the cement of various colours, yellowish, red, brown, bluish, is so completely conferruminated with the grains, that, upon breaking a specimen, the fracturing plane invariably passes through them, producing a uniformly smooth and frequently conchoidal surface. Sometimes both cement and grains are united into one homogeneous quartzy mass, in which, especially when thoroughly impregnated with oxide of iron, scarcely the slightest vestiges of former granulation remain perceptible. Such an extraordinary transformation of the cementing mass, observable not only in this but likewise in the quader-sandstone, the iron sand, and the variety of the newest sandstone called molasse, presupposes a state of liquefaction, and is but imperfectly accounted for by those who ascribe it to infiltration.

The result of another, equally enigmatical, liquefaction of siliceous matter, (which is, however, generally, though gratuitously, attributed to the agency of lightning) we see in the tubular concretions that have been found near Drigg in Cumberland, on the Senner heath in Westphalia, at Pillau in the vicinity of Konigsberg, at Halle upon the Saale, and, lastly, on the plains near Dibla in the Tibbou country. The African sand tubes differ from those of Drigg, as the sands themselves differ from each other in the two localities; the texture of the former is more homogeneous and pure, some being translucent and almost colourless; and, when cylindrical, not unlike some tubular varieties of stalactic carbonate of lime. Others are internally of a light-grey colour, here and there marked with white specks from semi-fused grains of sand: their outer surface is either approaching to smooth, or studded with snow-white opaque grains of sand, sunk in the vitrified substance; but they are not coated by the agglutinated sand which, in the English tubes, forms a rough crust, gradually passing into the vitreous substance of the sides. The stem, to judge from the short fragments I have seen, is very irregular in its circumference, and (except in the small cylindrical tubes, whose surface is even) polymorphously jagged, compressed, and contorted. Their interior lustre is superior to that observable in the European _Fulgurite, Astraphyalite, Ceraunian Sinter, Blitzröhren_,—names under which these tubular concretions have been introduced into our systems of mineralogy.

In most of the specimens of the variegated series described in the catalogue, the presence of common salt is obvious to the eye or the taste, or at least discoverable on the application of chemical re-agents. The tickets placed with No. 35. and some others, are inscribed “Aluminous slate;” but these specimens belong to the micaceous variety into which the red marle sandstone so frequently passes, and which sometimes forms distinct beds in it, overlaid by variegated and white marle slate; neither is the salt with which they are impregnated any other than muriate of soda.

The gypsum, of which some varieties are among the specimens found in the red marle, both at the most northern and the most southern points where Dr. Oudney collected, is of course referable to the newer, and some even to the newest, formation: it is mostly foliated-fibrous, and, in several specimens, intermixed with red clay.

I have little to say on the specimens of limestone enumerated in the list: most of them agree perfectly well with our new magnesian limestone; but external as well as chemical characters in detached fragments, not observed in situ, are but uncertain guides to the determination of the various modifications of Werner’s older fletz limestone, to which, I suppose, those specimens must all be referred.

There are only two specimens of common salt brought home, neither of which exhibit any thing peculiar in their appearance: but were they ever so numerous or remarkable in their exterior, they would not contribute greatly towards illustrating the history of the saline deposites and saliferous formations of the regions from which they come. The excessive abundance of salt in the variegated sand all over the central part of northern Africa, indicates either the existence of an extensive deposition of that substance beneath the prevailing rock formation, or the uninterrupted operation of causes by which those superficial saline masses, crusts, and efflorescences (the last of these observable in most specimens of sandstone brought from thence), are produced independently of briny waters emanating from such deposits of rocksalt. Mr. Keferstein, who has collected a multitude of instances of the occurrence of salt springs in situations which would seem to preclude the possibility of an immediate connexion between them and extensive beds of rock salt, has by ingenious reasoning and a number of interesting facts endeavoured to prove, that, in contact with waters circulating in the earth, the members of the saliferous formation (especially the clay to which, as an inseparable concomitant of salt, the name of _salzthon_ has been given) are endowed with the power of generating salt by means of a chemical process, of which the rationale (as that of many others) remains among the desiderata of the science.

Those who are of opinion that brine springs are, under all circumstances, derived from great salt formations, and that their rise and presence, in any given situation, may be satisfactorily accounted for, by hydrostatic pressure alone, will probably find nothing extraordinary in the peculiar occurrence of that substance in the clay of the extensive salt fields of Mafen, Hamera, &c.; they will consider the various forms under which it presents itself in those tracts merely as the result of aggregation of saline particles conveyed from the great depot to the crevices of the clay, gypsum, and sandstone, and left there by the simple process of evaporation. I shall not attempt examining which of the two theories derives most support from the different phenomena relative to the production of salt observed by you on your journey, or to the occurrence of fresh water springs in the centre of salt hills, dwelt upon by Herodotus, and other circumstances belonging to halurgic geology; but refer you, for materials necessary for this inquiry, to the important facts detailed by the abovementioned author in the second volume of his periodical work (Teutschland, geognostisch-geologisch dargestellt, Weimar, 1823), as also to those opposed to them by no less an authority than Mr. V. Langsdorff in his last work (Anleitung zur Salzwerkskunde, Heidelberg, 1824).

The specimens of trona (carbonate of soda), collected on the expedition, exhibit this salt in various degrees of purity. In some, it is mechanically mixed with muriate and sulphate of soda; in others, it appears, when divested of the casually adhering substances, to be perfectly pure. Of the latter, we have two very distinct varieties, as far, at least, as external characters are concerned. The one consists of layers, or crusts, of about one-third of an inch in thickness, opaque, and of a white colour, generally with an almost imperceptibly slight tinge of red; and yellowish stains are sometimes observable. These layers, when broken, display distinct concretions between lamellar and granular; the lower surface is rough, and more or less impure, the small interstices being partly filled up with reddish earthy matter; the distinct concretions terminate at the upper surface, in small, slightly cuneiform, apparently four-sided compressed prisms, acuminated by two planes which meet under an angle of about 95°; but both the lateral and terminal edges are constantly rounded off, and the planes uneven and striated. These crystals, not much inferior in hardness to carbonate of lime, are internally splendent, externally dull, and generally covered by a fine efflorescence, and also often studded with small limpid cubical crystals of muriate of soda. This variety is formed in the lakes of Ghraat, apparently in the same manner as the carbonate of soda (urao) of the Lagunilla lake of Venezuela, or that of the S. Macarius lake in Egypt, but appears to be less contaminated with other salts than either of these.

The other variety of carbonate of soda (the locality of which is doubtful, two tickets having been found accompanying the specimen, the one with “Kanem,” the other with “hills of Traghen,”) occurs in pieces which appear to have been part of a vein or layer. They are composed of groups of divergingly radiated acicular crystals, closely grown together, intermixed with indeterminable capillary crystals, confusedly aggregated. Some of these crystals appeared as very compressed four-sided prisms, indistinctly acuminated by two planes set on the acute lateral edges. Its fracture is lamellar-fibrous, passing into splintery; fragments wedge-shaped. Its colour is a dingy greenish, or yellowish-white, appearing brownish in the more compact parts of the pieces. The internal lustre is splendent; the external surface covered by a yellowish white powder. In the crystalline state, both these varieties of trona appear to be perfectly pure; it is, however, possible that they may differ from each other in the proportion of the water and carbonic acid with which the soda is combined in them. If, as Berthollet thinks, the origin of native carbonate of soda is to be looked for in the decomposition of common salt by carbonate of lime, we may farther conjecture, from the traces of bituminous matter found with the trona, that the rock instrumental to it is fetid limestone, beds of which are frequent concomitants of saliferous formations.

The following is the catalogue of the specimens of which I have been able to determine the localities.

1. Large grained granite; the deep-flesh-coloured feldspar in greater proportion than the greyish quartz, and the black, small-scaly mica. “From the Mandara mountains.”

2. The same; with feldspar of dirty-yellowish colour. From the Mandara range, and two similar varieties from the “hills of Dutchie Zangia, Soudan.”

3. Similarly coloured variety, but of smaller grain. From the same places.

4. Large grained variety of the same; the feldspar of a yellowish colour, and in a state of incipient decomposition, with little black mica. Mandara.

5. Variety similar to the preceding; in a state of disintegration: the feldspar decomposing into a reddish earth. From Quarra and Zurmee, Soudan.

6. Granite, both fine and coarse-grained, almost entirely composed of flesh-red feldspar, with indeterminable particles of a black substance, apparently mica. “From the high ridges of Zurma.”

7. The same, small-grained, rather slaty, approaching to gneiss, composed of greyish-white feldspar and quartz, with predominant black small-scaly mica. From Nansarena, Soudan.

8. Portion of a boulder, chiefly composed of fine-grained dirty-grey semicompact feldspar and some quartz; with disseminated particles of magnetic iron ore (a syenitic rock). “Found near Agutefa.”

9. Greenish-grey mica slate, with little admixed quartz and feldspar. “It forms the upper part of the ridges between Quarra and Zurma, Soudan.”

10. Yellowish-grey, soft, and friable mica slate. “From between Duakee and Sackwa, Soudan.”

11. A hard slaty mass, composed of brilliant silvery small scales of mica, penetrated by, or mixed with, brown and yellow hydrous oxide of iron. From the same.

12. White, massive, and irregularly crystallized fat quartz, stained by oxide of iron. “From a vein in the rocks of Quarra and Zurmee.”

13. The same, out of the granite of the Mandara mountains.

13. _a._ Yellowish and bluish-white quartz in large grains, as gravel. “From the bed of the river Yaou, seven days on the road to Soudan[126].”

14. Greyish-black close-grained basalt. “From the hills in the Sebha district.”

15. The same; with rarely disseminated grains of decomposing olivine. From the same.

16. The same; vesicular (basaltic amygdaloid), cells empty. Benioleed.

17. The same as the preceding, with disseminated granular particles, and minute acicular crystals of specular iron, which also mostly invest the irregularly shaped cells. “Benioleed; used for grindstones.”

18. The same, of a greyish-brown colour; cells elliptic, and partly filled with carbonate of lime. “Black mountains near Sockna.”

19. Greenish and yellowish grey, fine-grained crumbling sandstone. “Found with the gypsum of the hills to the northward of Om-el-Abeed.”

20. The same, brownish-yellow; “occurring in beds near Om-el-Abeed.”

21. The same, reddish and yellowish, fine-grained, rather friable. Wady Kawan.

22. Similar, reddish-brown variety of sandstone, but more friable than the preceding. Tadrart ridge.

23. The same, of a colour between grass and leek-green, fine-grained, very crumbling. “Traghen, under a gypsum crust; often in beds of from ten to twelve feet. It has the appearance of some of the soft sandstone in the mountain range near Tripoli.”

24. Yellowish-white friable sandstone, and fine sand, strongly impregnated with salt. “Under a calcareous crust, Fezzan.”

25. Similar sand of a very fine rounded grain. “From the Wady, in which is the Trona lake.”

26. Yellowish clayey sandstone, filled with small rounded quartz grains and minute white particles of small univalve shells, (Paludina?) “Gaaf.”

27. Fine and close-grained yellowish-white sandstone, of a thin stratified structure, which is distinctly seen at the disintegrated parts of the fragment. “Wady Katefa, under the basalt; forming fine precipitous walls in the middle of the range.”

28. Brownish-red friable sandstone; the rounded grains of various sizes, loosely united by clay. “Sandstone of the hills of Wady Ghrarbi. There is a finer and tender species, and also a stratiform one; but my specimens are lost.”

29. The same, of a similar colour, intermixed with yellowish, less crumbling, and containing pebbles. “From the hills to the westward of Hamera, on which the town is built.”

30. Sandstone of yellowish colour and fine-grained, faintly variegated with purple. Aghadem.

31. The same, fine-grained, white, with linear purplish streaks, being the edges of horizontal filmy depositions of iron ochre of that colour. Wady Kawan.

32. A similar variety, exhibiting purplish-yellow and red variegations, thoroughly impregnated with salt, which is also seen efflorescent on the surface. “Hills of Wady Ghrarbi.”

33. Similarly coloured sandstone, in laminar fragments, passing, by decomposition, into soft clay variegated with the same colours. Wady Kawar.

34. Tabular fragment of very close-grained nearly compact variegated sandstone; colours, purplish and two shades of yellow, in irregular stripes. “Sebha district.”

35. Purplish-brown slaty sandstone, micaceous on the planes of separation, passing into cream yellow and white clay-stone of the same structure. “Aluminous slate (sic) in different states, forming a considerable part of the mountain range, Tadrart, Tuarick country.”

36. A tabular fragment, like the preceding; micaceous on the rifts, of reddish-brown colour, being thoroughly penetrated by oxide of iron. Aghadem.

37. Yellowish sandstone, composed of round grains of quartz, with white clayey cement, which, towards the surface of the rolled piece, becomes quartzy. From ditto.

38. A similar large-grained variety, of reddish-yellow colour with brown streaks, in which the cementing clay, become quartzy, is scarcely distinguishable from the grains. “Forming the eastern boundary of the hills near Traghen.”

39. A large fragment of the same quartzy sandstone, of yellow colour, with red streaks and brown nucleus, nearly compact, so as to exhibit on its conchoidal fractural surfaces the traces only of a granular structure. “Strewed over the plain between Ghudwa and Mourzuk.”

40. The same, brownish-red, in the shape of a rolled amorphous fragment, having acquired a uniform glossy surface like red jasper. From ditto.

41. Yellowish variety of the same, the granular passing into compact structure. “Thick exposed beds from Om el Abeed to Sebha.”

42. Yellowish-grey variety of the same, as perfectly compact tabular fragments, having their surfaces studded with small polymorphous bodies imitating the appearance of parts of secondary fossils. From ditto.

43. The same as the preceding, having its surface marked by small bivalve shells, converted into the mass of the sandstone. From ditto.

44. Sharp-edged fragments, of a variety like No. 39., of a deep chocolate-brown colour and flat conchoidal fracture. “Between Sebha and Timinhint; rocks about 250 feet high.”

45. The same, in which the quartz grains are very firmly cemented by dark-red or brown siliceous iron-stone, sometimes enclosing larger rounded grains and small pebbles; the whole forming a very hard compact conglomerate with conchoidal shining fractural surface. “From between Om el Abeed to Sebha, and near Zuela.”

46. Fragment of a mass of quartzy sandstone and compact brown ironstone, externally stalactic reed-like, with black glossy surface. “From the hills of Wady Ghrarby.”

47. Brown ferruginous sandstone, nearly compact, and with drused cavities, enclosing yellowish nodules of magnesian limestone. “Forms the upper part of numerous low hills, and the surface of exposed parts on the road from Hamera to Zuela.”

48. A mass of yellow and brown ferruginous sandstone with amorphous botryoidal surface, unequally penetrated by siliceous brown oxide of iron, which produces the appearance of a mixture of brown ochrey clay-ironstone. “Near Timinhint, forming the summit of hills.”

49. Wood-hornstone; dark brown, with lighter coloured centre, being part of a cylindrical stem or branch of a dicotyledonous tree. “From between Mestoota and Gatrone.”

50. Flint composed of conchoidal distinct concretions, some of them forming nuclei; the layers of alternating brown and white colours, irregularly curved. “Quantities strewed over the plain from Temasta to Bonjem.”

51. Yellowish-grey flint passing into hornstone, in irregularly angular pieces, with brown glossy corroded surface. “La Saila; hills of silex and opal.”

52. White hornstone; a boulder with corroded glossy surface. “Strewed in large quantities between Wady el Beny and Wilkna, and on the summit of gypsum hills.”

53. Yellowish-white substance intermediate between hornstone and calcedony, in angular pieces, with cream-coloured cacholong on the surface. “On the way from Gatrone to Tegerhy.”

54. Brownish-red carnelian; a fragment, with irregularly botryoidal yellowish decomposed surface. From ditto.

55. Several fragments of variously shaped rough sand tubes; internal surface highly glazed. “From the sands near Dibla.”

56. Lithomarge, reddish-brown, here and there variegated with bluish-green and greyish, in fragments with rather tuberculated surface. “Aghadem, beds in the sandstone.”

57. The same, but penetrated by iron ochre, and much harder; with small imbedded pyriform concretions. From ditto.

58. Brownish-red and yellowish-grey variegated slaty clay, very soft and unctuous to the touch. From ditto.

59. Small-foliated amorphous gypsum, confusedly crystallized, with adhering red marl. “From the curiously formed gypsum hills of Bonjem to Hormut and Takui, with large quantities of opal on the top.”

60. Some specimens of white, granular, and foliated gypsum; one of the varieties composed of wedge-shaped laminæ. Bonjem.

61. Large-foliated white selenite. “Close to the Tchad, Kanem.”

62. Compact limestone, of bluish-grey colour, divisible into tabular fragments. “Benioleed, under the basalt.”

63. Light cream-coloured nearly compact limestone, in tabular fragments; fracture even, fractural surface slightly glimmering. Benioleed.

64. Fragment of a similar variety of limestone, with conchoidal fracture. “Benioleed, lowest observable stratum except one.”

65. Compact limestone, of a reddish and cream yellow colour, variegated with pale brown, of very close texture, and small-conchoidal fracture. “Hills to the north of Benioleed.”

66. Fragment of a greenish-grey tabular magnesian limestone, splendent on the fractural surfaces, the lustre produced by a curved-lamellar, though (in one direction) apparently compact structure. “On the ridges between Meshroo and Tegerhy.”

67. Yellowish-red, close-grained, nearly compact limestone, here and there with minute scales; external exposed surface uneven, glossy. “Temedetan, forming thick strata.”

68. Rolled fragment, of a reddish-yellow variety of magnesian limestone, with glossy surface, and of earthy fracture, including some dark-coloured grains, (oxide of manganese?) “Found in the deserts, sometimes finely dendritic.”

69. Light cream-coloured hard (magnesian) limestone, with earthy uneven fracture; the exposed surface shining, partly corroded, partly smooth. “Hills of Gaaf.”

70. A similar variety. “From the Assoud, Wady el Malagi.”

71. A rolled fragment of yellowish-grey compact limestone (magnesian), of even and dull fracture; the surface shining, wrinkled by decomposition. “To the north and south of the Wells of Mafrass.”

72. The same variety as the preceding, in the shape of a large conical lump, with uneven and corroded glossy surface, enclosing rounded pieces of the same limestone. From ditto.

73. A similar variety of magnesian limestone, forming a botryoidal group of more or less globular concretions, from upwards of half an inch to half a line in diameter, and intimately grown together with each other. “Meshroo and El Wahr.”

74. Yellowish limestone, of curved-lamellar structure. “Forming veins in the basaltic rocks in Agutefa.”

75. Brownish-yellow limestone, in stalagmitical irregular layers. “On the desert, between Mushroo and El Wahr.”

76. Another fragment, apparently part of a large stalagmitic nodule, in layers on a yellow granular mass of carbonate of lime. From ditto.

77. Greyish-brown and hair-brown fibrous limestone, in tabular pieces; the fibres perpendicular, or in an oblique direction to the horizontal planes, straight or slightly curved. In some specimens, the hair-brown layer is sard-onyx and onyx-like, succeeded by a red and a white stratum, the former generally in the form of a crust, with superficial small acute rhombohedrons of carbonate of lime; in others, the hair-brown layer is traversed by white veins. “Boundaries of Fezzan and Tuarick country.”

78. Sulphate of barytes; a group of bluish and brownish prismatic crystals, (var. rétrécie of Haüy), covered by red marle.

79. Common salt, in white, opaque, granular aggregations, externally stained by ferruginous clay. “Road between Hamara and Zuela.”

80. A saline incrustation, of yellowish-white colour, partly solid, in thin tables, partly in powder, composed of carbonate, muriate, and sulphate of soda. “Near Germa.”

81. Carbonate of soda (trona), thick-fibrous foliated, in crusts of the thickness of one-fourth to one-third of an inch, indistinctly crystallized on the upper surface. “From the trona lakes in Wady Trona.”

82. The same, studded on the upper surface with small limpid cubical crystals of muriate of soda. From ditto.

83. Carbonate of soda, of yellowish and greenish-grey colour, in masses with diverging radiated fracture. Kanem?

84. A rolled piece of nearly compact brown ironstone. “Upper strata from Aghadem to the southward of El Wahr.”

85. Compact brown ironstone, of dark brown colour; an irregularly tubercular nodule, with surface, particularly that of the old fractural planes, glossy, the recent fracture exhibiting a dull earthy surface. “From plains to the southward of Bonjem.”

86. Compact brown ironstone, of deep chesnut-brown colour, in rounded oblong pieces of from one-half to upwards of an inch in diameter, the whole glossy as if varnished; fracture even, earthy. From ditto?

87. Fragment of compact brown ironstone, mixed with much quartzy matter. Wady Kawar and Aghadem.

88. Massive and granular brown ironstone, mixed with much yellow iron ochre and sand. “In loose masses or crusts, on the top of the ridges between Sockatoo and Kashna, and on the low hills around Sockatoo.”

89. Fragments of clayey brown ironstone with ochrey nodules. “Wady Shiati hills.”

90. A mass, mixed, of brown ironstone and red and yellow iron ochre. “From the soil of Wady Sandalion, Tuarick country.”

91. Cubic fragments of common galena, (sulphuret of lead). Kanem, Soudan.

92. Pure tin, cast in moulds, in the form of thick wire. Brought from Soudan.

I conclude this long letter with mentioning a specimen of Roman cement, taken from the ruins of Ghirza, which, in parts where the admixture of small stony fragments is not observable, has very much the appearance of, and might easily be mistaken for, a granular-crystalline variety of tertiary limestone. It has unquestionably undergone a transformation: a circumstance which may, in some measure, serve to justify the remark of Lepère—“C’est le temps seul et non l’art qui manque à la pétrification absolue de nos mortiers et cimens; nos neveux diront de nos constructions ce que nous disons de celles des anciens.”

I have the honour to be, my dear Sir,

Yours very faithfully,

CHARLES KONIG.

To Major Denham, &c.

FOOTNOTES:

[Footnote 126: Three very interesting bivalve shells, distinct, it appears, from the other species of the genera to which they respectively belong, have been discovered in the above-mentioned river by Major Denham. The first, a species of ÆTHERIA, I distinguish as

ÆTHERIA _Denhami_: testa irregulariter rotundato-oblonga, ad cardinem gibbosa, utriusque valvæ callo cardinali basim versus oblique truncato.

Hab. in Africæ interioris fluvio Gammaroo.

The form of the cardinal callosity to which the semi-internal ligament is attached affords a distinction sufficiently characteristic of the species: its oblique truncating plane, which extends towards the rather indistinct umbo, is, in the closed state of the shell, in partial contact with that of the corresponding and similarly formed callus of the other valve. The general form of the shell is oblong or rounded, but appears to be subject to considerable variation: one of the specimens before me exhibits the exterior of Lamarck’s A. _transversa_, which latter is no doubt a casual variety only of the other species described and figured by that naturalist.

These shells are externally furnished with a blackish-brown epidermis; beneath this a white film is deposited, on the removal of which a beautiful pearly naker appears, similar to that of the internal surface of the valves. The blistered appearance of the interior of both the valves is constant in all specimens, and may, as intimately connected with the structure of the shell, be considered of sufficient importance to be admitted into the distinctive character of the genus.

Lamarck, imagining that these shells live at the bottom of the sea, named the genus, as he says, after one of the daughters of Oceanus. Though the Ætheriæ are now well known to be fluviatile shells, the emendators of zoological nomenclature may still be exonerated from framing a new name for this genus, since the old one is derivable from the original locality of its species; a part of central Africa having, according to Pliny, been anciently known by the appellation of _Ætheria_.

The second shell, a new species of IRIDINA, may be thus characterized:

IRIDINA _Oudnæi_: testa transversa ovato-lanceolata tumidiuscula, cardine stricto sub-edentulo, basis margine sinuato.

Hab. cum priore.

This species is very distinct from E. _elongata_ in form and in the hinge line being without crenulation; and from E. _nilotica_, which it resembles in the latter of those characters, it differs by its form, inferior thickness, and iridescence. The length of the specimen before me is 4⅔, its greatest breadth at the umbo nearly two inches. Placed on the basal edge, which is concave, the anterior side presents a considerable slope from the umbo to the exterior margin, which gives the valves a tapering or ovate-lanceolate form. The external epidermis, of a greenish-brown colour, exhibits slightly undulating striæ of growth. The interior surface is slightly uneven-undulated, white, with delicate opalescent colours, green and faint pink; the former chiefly disposed in spots. The muscular impressions are more slightly marked than in the other species.

For the third shell, which I considered as a new species of ANODON, I propose the name of

ANODON _Clappertoni_: testa transversim oblonga, antice in extremo cardine acute excisa.

Hab. cum antecedentibus.

The notch at the anterior extremity of the hinge being always acute, never obtusangular or rounded, I have confined myself to it in the distinctive character of this species, which differs in several other respects from ANODON _purpureus_ and _rugosus_ of Swainson, to both of which it is, however, nearly related. The size of the shell, in the several specimens before me, varies from 1½ by ¾ of an inch to 3 inches by nearly 1½. Its form is transverse-oval, with a slight slope at the anterior end. The hinge margin is straight. Epidermis olive-green, appearing of a reddish-brown colour, owing to the pink colour of the surface underneath, which latter in one specimen passes into bluish-green at the umbones. Muscular impressions three; one of them, at the anterior end, oval, and continued in a faint tapering form towards the hollow of the umbo; of the two other impressions, which are both stronger marked, the one nearest to the edge of the valve is oval, with a small rounded sinus at the inner border, and close to it a smaller irregularly oval mark with notched margin: the two principal marks are connected by the edge of the impression of the mantle, the smaller mark being placed within the line. The tinge of the internal surface is pink, imperfectly painted over as it were with white. The several specimens, in different stages of growth, exhibit all these characters; there is, however, among them a single valve of rather larger dimensions and more rounded than the rest, with a fine bronze-coloured internal surface like that of IRIDINA _nilotica_. Whether this is to be considered as a distinct species, or only as a variety indicative of the full grown state of the shell, I must leave to the decision of conchologists more experienced in discriminating the ambiguous species of this genus.]

No. XXIV.

_Thermometrical Journal kept at Kouka in Bornou._