Chapter IX: Geographical Distribution (3)

A. The Polycystine marl of Barbados appears at different parts of the
island to present greater variations in its petrographical and
zoographical composition than would appear from Ehrenberg's description
(1875, L. N. 25, pp. 106-116). Through the kindness of one of my former
students, Dr. Dorner, to whom I take this opportunity of expressing my
thanks for the favour, I received a large number of specimens of Barbados
rock, taken from various parts of the island, and they exhibit very great
variations in their external appearance, their chemical composition, and
the {clxxi}Radiolaria which they contain. The white specimens resembling
Kieselguhr contained approximately 60 to 70 per cent. by volume of
Radiolarian shells, the yellowish marl 40 to 50 per cent., and the brown
and black (bituminous) marl 10 to 20 per cent. or less. Two analyses of
the first, which my friend Dr. W. Weber was good enough to carry out,
yielded different results from those which are given by Ehrenberg on the
basis of Rammelsberg's analyses (L. N. 25, p. 116). The results of both
are here given for comparison.

--------------------------------+--------------------------+-------------
Ehrenberg-Rammelsberg | Weber I. | Weber II.
(Fragment from Hillaby). | (Chalk-like Fragment). |(Tripoli-like
| | Fragment).
--------------------------------+--------------------------+-------------
Silicate of alumina, 59.47 |Silica, 52.2 | 71.3
Alumina and oxide of iron, 1.95 |Alumina (with traces |
Calcium carbonate, 34.31 | of oxide of iron), 12.3 | 11.2
Water, 3.67 |Lime and magnesia, 31.9 | 14.8
|Carbon dioxide, 3.2 | 2.7
______ | _____ | _____
Total, 99.40 | Total, 99.6 | 100.0
--------------------------------+--------------------------+-------------

For further comparison I here add the three different analyses of Miocene
Tripoli-marls from Sicily, given by Stöhr on the authority of Fremy,
Schwager, and Mottura (Tagebl. d. fünfzigsten Versamml. Deutsch. Naturf.
u. Aertzte in München, 1877, p. 163).

--------------------------+-------------+--------------+-------------
Composition. |Tripoli from | Tripoli from | Tripoli from
| Licata | Grotte | Caltanisetta
| (Fremy). | (Schwager). | (Mottura).
--------------------------+-------------+--------------+-------------
Silica, | 30.98 | 58.58 | 68.6
Alumina, | 17.54 | 11.51 | }
Oxide of iron, | 0.33 | 1.84 | } 3.6
| | |
Lime, } | 38.09 | { 8.49 | }
Magnesia, } | | { 0.41 | } 12.1
| | |
Water and organic matter,}| | { 11.26 | }
Carbonic acid, }| 13.06 | { 7.12 | } 15.2
+-------------+--------------+------------
| 100.00 | 99.21 | 99.5
--------------------------+-------------+--------------+-------------

B. The Radiolarian marl of the Mediterranean appears, judging by the
accounts already published, to stretch along a considerable part of the
coast in the earlier and middle Tertiary formations; thus it occurs of
similar composition in widely separated localities, in Sicily, Calabria,
Zante, and Greece; in North Africa from Tripoli to Oran and probably much
farther. So long ago as 1854 Ehrenberg, in his Mikrogeologie (L. N. 6)
gave a series of important, even if incomplete, communications regarding
the "chalky white calcareous marl of Caltanisetta" (Taf. xxii.), the
"Platten marl of Zante" (Taf. xx.), the "plastic clay of Ægina" (Taf
xix.), and the "polishing slate of Oran" (Taf. xxi.). In 1880 Stöhr
showed in his fundamental description of the Tripoli from {clxxii}Grotte
in Sicily (L. N. 35) that its Radiolarian fauna is much richer than
Ehrenberg supposed. The same is the case in the Tripoli of Caltanisetta,
and also in the Baden marl of the Vienna basin. The richest deposit
appears to be the pure Kieselguhr-like Tripoli from Oran; a small
specimen, which was recently sent to me by Professor Steinmann of
Freiburg, i. B., contained many hitherto undescribed species, and was at
least as rich as the purest Barbados marl.

247. _Radiolarian Clays._--Among the Radiolarian or Polycystine clays we include the firm, often plastic, formations, which contain a larger proportion of Radiolaria than of other organic remains. The first of these to be mentioned is the Cainozoic formation of the Nicobar Islands in Further India, which rises to a height of 2000 feet above the level of the sea, and consists for the most part of coloured masses of clay of varying constitution; on Car Nicobar these are mostly grey or reddish, on the Island of Camorta they are partly strongly ferruginous and red and yellow (_e.g._ at Frederickshaven), partly white and light, like meerschaum (_e.g._ at Mongkata). The latter varieties appear to pass over into pure loose Polycystine marl like that of Barbados, the former into calcareous sandstone. Although the Polycystine clays of the Nicobar Islands are as yet only very incompletely known, it may be concluded with great probability that they are true deep-sea formations and nearly allied to those recent forms of red clay, which by their abundance in Radiolaria most nearly approach the Radiolarian ooze, such for example as the red clay of the North Pacific between Japan and the Sandwich Islands (Stations 241 to 245, compare §§ 229 and 239). With this view agrees also the greater or less quantity of pumice dust and other volcanic products. Probably Radiolarian clays like those of the Nicobar Islands occur also in other Tertiary rocks; part of the Barbados marl passes by gradually increasing content of clay into such; and in this case also the amount of included pumice is often considerable. Many mixed Radiolarian marls of the Mediterranean (_e.g._, of Greece and Oran) also appear to pass over at certain points into Radiolarian clay.

The Radiolarian clays of the Nicobar Islands are unfortunately very
incompletely known both as regards their geological nature and their
palæontological composition. The communications of Rink (Die
Nikobaren-Inseln, eine geographische Skizze, Kopenhagen, 1847) and of
Ehrenberg (L. N. 6, p. 160 and L. N. 25, pp. 116 to 120) leave many
important questions unanswered. The latter has only figured twenty-three
species in his Mikrogeologie (L. N. 6, Taf. xxxvi.). In his tabular list
of names (L. N. 25, p. 120) he only incompletely records thirty-nine
species, although in 1850, immediately after the first examination of the
Nicobar clay, he had distinguished "more than a hundred species, partly
new, partly identical with those of Barbados" (L. N. 16, p. 8). I have
unfortunately been unable in spite of many efforts, to obtain for
investigation a specimen of Nicobar clay. The only microscopical
preparation (from Ehrenberg's collection), which I was able to examine,
contained several hitherto undescribed species. A thorough systematic
examination of these important Radiolarian clays is a pressing necessity,
especially as they seem to be markedly different from those of the
Mediterranean (from Ægina, Zante, &c.).

{clxxiii}248. _Radiolarian Quartzes._--Under the name Radiolarian or Polycystine quartzes are included those hard, siliceous rocks, which consist for the most part of the closely compacted shells of SPUMELLARIA and NASSELLARIA. To these "cryptocrystalline quartzes," or better, quartzites, belong more especially the pure Radiolarian formations of the Jura, which have been described as flint, chert, jasper, as well as other cryptocrystalline quartzites. Most of the rocks of this nature hitherto examined are from Germany (Hanover, South Bavaria), Hungary, Tyrol, and Switzerland; others are known from Italy (Tuscany). They occur both in the upper and middle, but especially in the lower Jurassic formation (also in the lower layers of the Alpine Lias). A small part of them has been examined in their primary situation (the red jaspers of Allgäu and Tyrol), the greater part, however, only as loose rolled stones in secondary situations (thus in Switzerland in the breccia of the Rigi, in the conglomerate of the Uetli-Berg, and in many boulders of the Rhine, the Limmat, the Reuss, and the Aar). The greatest abundance, however, of Jurassic Radiolaria has been yielded by the silicified coprolites from the Lias of Hanover. These "Radiolarian coprolites" are roundish or cylindrical bodies, which may attain the size of a goose-egg; they probably originated from Fish or Cephalopods, which had fed upon Crustacea, Pteropoda, and similar pelagic organisms, whose stomachs were already full of Radiolarian skeletons. Next to the coprolites the richest is the red jasper, whose colour varies from bright to dark red; it constitutes a true "silicified deep-sea Radiolarian ooze." The "_Aptychus_ beds" also of South Bavaria and Tyrol are very rich, and have furnished about one-third of all the Radiolaria known from the Jura; most of the species too are very well preserved (compare § 243).

Regarding the remarkable composition and manifold varieties of the
Jurassic Radiolarian quartz, the very full treatise of Dr. Rüst may be
consulted (L. N. 51). The very interesting Radiolarian coprolites, which
that author has discovered in the lower and middle Jura of Hanover, occur
in astonishing numbers in the iron mines at the village of Gross-Ilsede,
four and a half miles south of the town of Peine. They constitute from 2
to 5 per cent. by weight of the Liassic iron ore; of this latter, in the
year 1883 alone, not less than two hundred and eighty million kilograms
were excavated. It is very probable that the careful microscopic
examination of thin sections of coprolites, as well as of flints, chert,
jasper, and other quartzites, would yield a rich harvest of fossil
Radiolaria in other formations also. In Italy Dante Pantanelli has
discovered interesting Polycystine jaspers in Tuscany (L. N. 36, 45);
these also appear to occur in the Jura (compare § 243, and L. N. 51, pp.
3-10).

249. _Fossil Groups._--The preservation of Radiolaria in the fossil state is, of course, primarily dependent on the composition of their skeleton. Hence the ACANTHARIA, whose acanthin skeleton although firm is readily soluble, are never found fossil. The same is true of the skeletons of the PHÆODARIA, which consist of a silicate of carbon; here, however, a single exception is found in the Dictyochida, a subfamily of the Cannorrhaphida, the isolated parts of whose skeletons appear to consist of pure silica, and {clxxiv}are often found fossil. Of the two other legions those families which possess no skeleton are of course excluded; the Nassellida among the NASSELLARIA, and the Thalassicollida and Collozoida among the SPUMELLARIA. Thus of the 85 known families there remain scarcely 55 of which the skeletons may be expected in the fossil state; and of these scarcely half have been actually observed in this condition. Of the 20 orders of this class enumerated in § 155, the following 9 may be, for palæontological and geological purposes, completely excluded:--(A) The 4 orders of ACANTHARIA (1, #Actinelida#; 2, #Acanthonida#; 3, #Sphærophracta#; 4, #Prunophracta#); (B) 3 orders of PHÆODARIA (5, #Phæosphæria#; 6, #Phæogromia#; 7, #Phæoconchia#); (C) 1 order of NASSELLARIA (8, #Nassoidea#); (D) 1 order of SPUMELLARIA (9, #Colloidea#). From a geological point of view the following 6 orders, although occasionally found fossil, are of quite subordinate importance:--(A) Among the SPUMELLARIA (10, #Beloidea#, and 11, #Larcoidea#); (B) among the NASSELLARIA (12, #Plectoidea#; 13, #Stephoidea#; 14, #Botryodea#); (C) among the PHÆODARIA (15, the #Phæocystina#). On the other hand the following 5 orders, which are the main constituents of Radiolarian rocks, are of pre-eminent geological importance:--(A) Among the SPUMELLARIA (16, #Sphæroidea#; 17, #Prunoidea#; 18, #Discoidea#); (B) among the NASSELLARIA (19, #Spyroidea#, and 20, #Cyrtoidea#). The numerical relation in which the different families of these orders appear in the Radiolarian formations may be seen on consulting § 157.

250. _Fossil and Recent Species._--The fact that there are many Radiolaria living at the present day, whose shells are found fossil in Tertiary rocks, is of great phylogenetic and geological significance. This appeared to be the case even from the older observations upon the Polycystina of the Barbados marl (see note A), but more recent and extensive observations both upon these and upon the Miocene Radiolaria of Sicily, have shown that the number of these "living fossil" forms is much greater than was previously supposed (see note B). Among the Miocene Radiolaria numerous species, both of SPUMELLARIA (especially #Sphæroidea# and #Discoidea#) and of NASSELLARIA (especially #Spyroidea# and #Cyrtoidea#) are not to be distinguished from the corresponding still living forms (see notes C, D). On the other hand, those genera, which are rich both in species and individuals (recent as well as fossil), present continuous series of forms which lead gradually and uninterruptedly from old Tertiary species to others still living, which are specifically indistinguishable from them. These interesting morphological facts are capable of direct phylogenetic application, and furnish valuable proofs of the truth of the theory of descent.

A. Ehrenberg, in his list of fossil Polycystina (L. N. 25, pp. 64-85,
1875), records 325 species of which 26 are still living.

{clxxv}B. Stöhr, in his list of Miocene Radiolaria from Grotte (L. N. 35,
p. 84, 1880), records 118 species, of which 29 are still living.

C. Teuscher, who at my request has made a large number of comparative
measurements and drawings, both of fossil and living Radiolaria, comes to
the conclusion that numerous SPUMELLARIA and NASSELLARIA from Barbados
are to-day extant and unchanged in the Radiolarian ooze of the deep
Pacific Ocean (compare § 242A, and p. 1760, Note).

D. From the comparative investigations, which I have made during the last
ten years into the recent deep-sea Radiolaria of the Challenger
collection and the Miocene Polycystina of Barbados, it appears that about
a quarter of the latter are identical with living species of the former.

{clxxvi}BIBLIOGRAPHICAL SECTION.