Chapter IV: Part 4

(8) _Valleys Excavated Between Successive Depositions of Drift._ A closely related, but not identical, point may be found in the extent of the valley excavations which can be proved to have taken place between the deposition of the earlier and later drift. We do not refer to valleys excavated in the drift especially, but to those excavated in other formations as well. If it can be shown, for example, that after the deposition of an earlier drift sheet, and before the deposition of a later, valleys were excavated which extended not merely into the drift itself, but far beneath the drift into the underlying rock, these valleys would be conclusive evidence of a long interval between the deposition of the two bodies of drift. The argument is of especial force when such excavations in the rock beneath the drift can be shown to have taken place at great distances within the margin of the newer drift. For valleys in such situations imply that the ice had receded at least as far to the north as they lie, during the interval between the two drift depositions, and may be so situated as to show that the ice had wholly left the drainage basin where they occur.

The absence of evidences of deep valley excavations in any given region during a supposed interglacial epoch, is no proof that such interval did not exist. The conditions may not have been everywhere favorable for erosion within the limits of any narrowly circumscribed area, and the absence of interglacial valleys would be only negative evidence against an interglacial epoch. The absence of such evidence everywhere would bear against the existence of an interglacial epoch of much duration in such wise as to be more than negative evidence.

(9) _Different Directions of Movement._ If, after its maximum advance, the ice suffered merely a minor recession and then remained stationary, or nearly so, for a time, the general direction of its movement in a subsequent advance would probably be essentially the same as in the earlier. But if, after its maximum advance, the ice receded to a great distance, and especially if it entirely disappeared, a subsequent ice-sheet might have a very different direction of movement, since its center of accumulation and dispersion might be very different. It is conceivable that this center might shift during the history of a single ice-sheet. In this case there should be a gradual change in the direction of ice movement, not an abrupt one. If, therefore, there be found one sheet of drift made by an ice movement in one direction, overlaid by another sheet of drift deposited by ice moving in a very different direction, with an abrupt transition between them, such drift sheets would be presumptive evidence of distinct ice epochs. An exception would need to be made in the case of drift sheets along the margins of confluent or proximate ice lobes. In such cases, if the one lobe temporarily secured the advantage of the other, drift beds formed by movements from opposite directions might be found in vertical succession, without being evidence of separate ice epochs.

It is no part of the purpose of this essay to point out the difficulties which might arise in the application of this criterion of diverse directions of ice movements. It is possible that gradual changes in the direction of movement might leave records which would seem to indicate abrupt changes instead. This possibility makes care necessary in the application of the criterion, but does not destroy its value. When not itself conclusive, this criterion may be so associated with differential weathering, differential erosion, forest beds, etc., that their combined testimony makes but one conclusion possible.

The absence of evidence of radically diverse directions of movement during the time of deposition of the various sheets of drift, would be no proof that there were not distinct epochs. In the first place, the movements of different epochs might be harmonious--a condition of things more probable than any other if the more common views of the causes of glaciation be correct. In the second place, if the movements were diverse, the deposits might still be so similar that their differentiation, when the one is buried, might not be easily made. In the third place, the later ice might have so far incorporated the older drift material with that which belonged more properly to it, as to have destroyed all definition between them.

(10) _The Superposition of Beds of Till of Different Physical Constitution._ After the retreat of an ice-sheet, the surface of the country thus discovered would be largely mantled with drift. This drift would serve to protect the underlying rock from disintegration. But where there was little or no drift, the rock surface would be subject to all the disrupting agencies which affect surface rocks. The same would be true of all rock surfaces bared by subaërial erosion after the disappearance of the ice. Under these conditions, if a second sheet of ice invaded the region in question after it had been long exposed, it would find a surface prepared to yield large bowlders. The result would be the deposition of a new sheet of drift containing bowlders much larger than those which would have been proper to an ice-sheet overspreading a surface but recently abandoned. If, therefore, in the upper of two layers of subglacial till, bowlders of great size predominate, as compared with those of a lower homologous layer, they may be indicative of a great interval of time between the deposition of the upper and lower beds of drift. If the home of these bowlders be far north of the limit of the lesser sheet of drift, the distance, as well as the duration, of the ice retreat must have been great, and the reference of the two beds of till to distinct ice epochs would be favored. The case might be so strong as to make no other interpretation possible. Where in itself inconclusive, this criterion would have corroborative significance. In its application, the discrimination of subglacial and superglacial till would be imperative.

The absence of physical dissimilarity between superposed layers of subglacial till would not be proof of the absence of separate glacial epochs. The phenomena constituting the criterion could hardly be expected to be of common occurrence. They would never be obtrusive, and may easily have escaped attention where they exist.[17]

[17] The 10th criterion, in the order here named, was suggested by Mr. McGee in the discussion which followed the reading of the paper at Ottawa.

(11) _Varying Altitudes and Attitudes of the Land._ Another line of argument has to do with the altitude and attitude of the land during the deposition of various members of the drift complex. If during the deposition of one part of the drift that part of the continent covered by the outer part of the ice was low, the drainage from it would be sluggish. If the deposits of this drainage persist to the present time, we may find in their character evidence of the nature of the drainage, and therefore of the attitude of the land. If at a later time of drift deposition the glacial drainage in the same region was more vigorous, the deposits made by the glacial streams would be correspondingly coarser. In these deposits, if they persist to the present day, we should find conclusive evidence of the swiftness of the streams. If it can be shown that during the deposition of one sheet of drift drainage was sluggish, and that during the deposition of a later body of drift the drainage was vigorous, these facts are evidence of an interval between the two times of drift deposition, sufficiently long to accomplish the corresponding changes in elevation or attitude. Since such changes of altitude and attitude are generally believed to have been accomplished slowly, the interval must be believed to have been of considerable duration.

It is true that continental altitudes and attitudes might change during a single epoch of glaciation. If the change thus brought about resulted in increased slope, the more sluggish drainage of the earlier part of the epoch would be gradually transformed into the more vigorous drainage of the later part. In this case, if the evidence of both the earlier sluggish drainage and of the later vigorous drainage remain, there should also remain the evidence of the intermediate stages. If the deposits representing the intermediate condition of drainage do not exist, while those representing both extremes do, there would be the best of reason for believing that the intermediate phases of drainage did not exist during a glacial epoch, but during an interglacial epoch, when streams were not handling glacial debris, and when they were eroding rather than depositing. The deposits of the slow and of the swift drainage might occur in such relations as to prove, beyond peradventure, that intermediate stages of _glacial_ drainage never existed.

If the sluggish drainage accompanied the maximum ice invasion, while the vigorous accompanied a lesser, the evidence of the swift streams might be found far north of the southern limit of the earlier drift. The farther north of the outer border of the older drift the gravel representing the vigorous drainage of the later and minor ice-sheet occurs, the further the ice must have retreated before the change from the one type of drainage to the other was effected. On the other hand, the farther north of the limit of the later ice advance the sluggish drainage accompanying the earlier ice-sheet may be traced, the farther must the ice have receded before the changes resulting in vigorous drainage occurred. Under certain relations, the retreat of the ice might be shown to have been great enough, before the orographic movements which altered the nature of the drainage, to constitute in our judgment, a re-advance a distinct ice epoch. If for example throughout the course of a long river whose basin was largely covered with ice, there be evidence that sluggish drainage obtained during the maximum ice advance, and during all stages of the ice retreat until the basin was free from ice, and if there be evidence of a vigorous glacial drainage in the same valley at a later time, with no gradations between the two types, we have proof positive of at least a great recession, and of a considerable elevation of the land after the ice had receded beyond the limits of the drainage basin and before it again reached it in its re-advance. We hold that these phases of glacial drainage deposits may be so related to each other, to the valleys in which they occur, and to more or less distinct bodies of glacier drift, as to prove so great a recession of ice between the diverse phases of drainage deposition, as to constitute the second advance a distinct ice epoch.

The absence of evidence that the land stood at different elevations during different parts of the period of drift deposition, does not in any way militate against the theory of recurrent and distinct ice epochs. A constant attitude of the land is the thing to be assumed, until positive evidence to the contrary is adduced.

(12) _Vigor and Sluggishness of Ice Action._ If it can be shown that during one epoch of glaciation, we will say the epoch of maximum ice extension, the ice action was relatively sluggish, while during a later and minor advance its action was vigorous, the difference of action might be regarded as presumptive evidence of distinct ice epochs. Evidence of the two phases of ice action here referred to are difficult of definition, but they have been independently noted by more than one glacialist. It is true that a forward oscillation of the ice edge might be more forceful than an earlier forward movement which might have reached a greater extension. In itself, therefore, this line of evidence can not be regarded as possessing great value.

It has been indicated that under certain circumstances, and in certain relations, some of the foregoing criteria, taken singly, may be conclusive of glaciations so distinct from each other, as to make their reference to separate epochs proper. But where the facts and relations which constitute one of the criteria are found, the facts and relations constituting one or more of the others are likely to be found as well. Where two of the foregoing criteria are found to be coexistent, their joint force is greater than that of either one. If neither one be absolutely conclusive, the two may still be, since the one may exactly meet the deficiency of the other. If three or more concurrent lines of evidence exist in any locality, the case is still further strengthened. We maintain that several of the foregoing criteria may be so related to each other and to the formations concerned, as not only to make the recognition of separate ice epochs proper, but to make the failure of such recognition altogether unscientific. Even when a single line of evidence, or when double, or triple, or quadruple lines of evidence are not absolutely conclusive in ruling out every conceivable technical escape from the conclusion that there were separate ice epochs, their cumulative and corroborative force may still be such as to carry conviction scarcely less positive than that which mathematical demonstration would afford. In the nature of the case not all of these various lines of evidence could be expected to be found in any one locality, or perhaps in any one limited geographic area, but where one occurs, some or all of the others are liable to be found under favoring circumstance. The number of criteria, and the great extent of area where they may hope for application, afford great possibilities.

From the foregoing discussion, it will be readily seen that the nature of the criteria and the limitations imposed upon their application by the difficulty of proving stratigraphic continuity in such a formation as the drift, necessitate the greatest care in their use, and reduce the value of hasty and inexpert conclusions to a minimum.

IV. =Areas Where the Criteria find Readiest Application.=

The foregoing criteria find their readiest application in regions where a later sheet of drift, suspected of belonging to a later ice epoch, failed to reach the border of an earlier sheet of drift, suspected of belonging to an earlier ice epoch. The 1st, 2d, 3d, 4th, 5th and 10th as enumerated above, find their application wholly within the area affected by the drift of the separate epochs, if such there were. While within this general area they may be looked for at any point, they are likely to be of rare occurrence, except along a somewhat narrow belt, say 50 to 100 miles, adjacent to the border of the lesser ice advance. The conditions for their occurrence and detection are greatly favored if the lesser drift sheet be the later. The 6th, 7th, 9th and 12th criteria might hope for application within the same belt, but especially along a narrow zone on either side of the margin of the later drift sheet. It is along this zone that the types of surface are thrown into sharpest contrast, both as to material and topography. The 8th and 11th criteria have still wider limits of application, both within and without the border of the lesser ice advance.

=Rollin D. Salisbury.=

=_Editorials._=

It is the chief function of the national, state and provincial geological surveys to bring forth the great concrete facts relative to the structure and resources of their several fields. Within their special domains they also do an important work in the correlation of structures and formations, in the systematic aggregation of the facts, in the organizing of results, and in the development of the fundamental principles of geological science. To some extent they are permitted to do this beyond their own fields, but in the main the boundaries of these fields are the limits of their coördinations. They therefore leave a great function to be performed by some other agency in the coördination of interstate, international, and intercontinental factors. They are also restrained by their relationships to a somewhat too narrowly utilitarian public from devoting much direct attention to the solution of the deeper and broader problems that constitute the soul of science, though their contributions bear upon these in the most radical and important way. In the primary work of systematic observation, and the development of the immediate conclusions that spring therefrom, these surveys surpass all other agencies in the value of their contributions to the growth of the science, but in the secondary and ulterior work of correlation, in the synthetic aggregation and organization of results, and in the analytical and philosophical treatment of the whole, they need to be supplemented by agencies whose facilities and limitations lie in other lines, agencies whose relations and dependencies are complementary in nature. This secondary and ulterior work, in some degree, has been done by individual master students of systematic and philosophical geology, but to a very great extent it has not been done at all. It is a function which properly falls to universities, if the universities can only rise to meet it; for it is the function of universities, in the larger modern view, not only to rehearse science, nor merely even to educate young geologists, important as that is, but to develop science for science's own sake, and for its own inherent and permanent utilities as distinguished from its immediate applicabilities. To fulfill this function they must not only realize and appreciate it, but they must be equipped for field and experimental work, as well as library and laboratory study. Ideal correlations and academic systematizing are as apt to be hindrances as helps to the progress of science. While a few of the great universities of this country and Europe have made notable advances in these directions, the universities are, on the whole, far behind the great surveys in the performance of the work which properly falls to them. This is due not so much to a lack of appreciation of the function as to the lack of facilities.

With the development of this higher function of the universities there goes a coördinate function for a university journal of geology, a journal whose special efforts shall be devoted to promoting the growth of systematic, philosophical, and fundamental geology, and to the education of professional geologists. No part of the wide domain can wisely be neglected by any journal, but there seems to be an open field for a periodical which specially invites the discussion of systematic and fundamental themes, and of international and intercontinental relations, and which in particular seeks to promote the study of geographic and continental evolution, orographic movements, volcanic coördinations and consanguinities, biological developments and migrations, climatic changes, and similar questions of wide and fundamental interest. This field is not likely to be successfully cultivated except by a systematic endeavor, pursued through a period of years, to bring together the latest and best summations of the results attained in the several national fields in a common medium, where they can be compared and discussed, and where tentative correlations will suggest themselves, out of which, in turn, working hypotheses will naturally spring, leading on to such direct investigations as the nature of each question invites. It would be presumptuous to assume that the =Journal of Geology= can cultivate with more than very partial success this field, but it especially invites contributions of this class.

Another phase of geology which is thought to stand in much need of active cultivation is found in the clear and sharp analysis of its processes, the exhaustive classification of its phenomena, especially on genetic bases, the development of criteria of discrimination, the more complete evolution and formulation of its principles and the development of its working methods. The recent opening of new fields of research and the rapid progress of several new and important departments of the science give peculiar emphasis to this need. The rising generation of geologists, the hope of the science, should be schooled in these latest and most critical aspects of the science. A department of the =Journal=, entitled "Studies for Students," has been opened for the special cultivation of this field and for its adaptation to advanced students and progressive teachers of geology. Mere elementary presentations of processes and principles are not desired, but searching and critical expositions are solicited suited to the needs of young geologists who seek the highest professional equipment, and to progressive teachers who desire the fullest practicable command of the newest developments of the subject. These contributions may not be without their value to those who have already borne a considerable part of the heat and burden of life's professional day.

It is our desire to open the pages of the =Journal= as broadly as a due regard for merit will permit, and to free it as much as possible from local and institutional aspects. It will have the very important advantage of being published under the auspices and guarantee of the University of Chicago, and will be free from the usual financial embarrassments attending the publication of a scientific magazine. This necessarily imposes upon the local editors the immediate responsibility for its editorship. Beyond this, it is hoped that its institutional relationship will disappear entirely in an earnest effort to promote the widest interests of the science. As an earnest of this wider effort several eminent geologists, representing some of the leading universities of this country, and some of the great geological organizations of Europe, have kindly consented to act as associate editors.

T. C. C.

Upon invitation of the World's Congress Auxiliary of the World's Columbian Exposition committees were appointed by the several sections of the American Association for the Advancement of Science at its Rochester meeting to coöperate with it in completing the organization of scientific congresses to be held at Chicago in connection with the forthcoming World's Fair. The committee appointed by the geological and geographical section consisted of Thomas C. Chamberlin, John C. Branner, Grove K. Gilbert, W. J. McGee, Rollin D. Salisbury, Eugene A. Smith, Charles D. Walcott, J. F. Whiteaves, Geo. H. Williams, H. S. Williams and N. H. Winchell.

It has been arranged that this committee should undertake the work of preparing the scientific program for the Geological Congress. The committee have prepared a provisional schedule of topics, which they have submitted to the Advisory Council for revision. It has seemed to the committee that all contributions should be such as to have an international interest. Preferably, they should be subjects that can only be treated most advantageously in such a congress, especially those that involve the bringing together of data from different lands for comparison. The committee suggest the organization of the subjects under the following general classes:

=First.= Such as shall show the present state of geological progress. It is believed that this can best be done by an exhibition of geological maps which shall show the latest and best results of official and other surveys. As such maps will be prepared, it is hoped, for the World's Fair, duplicates can be made at a slight expense for the use of the Congress. It is hoped that each country that has made any notable progress in mapping its geological formations will furnish for the Congress at least a general geological map, if not also special or analytical maps.

=Second.= Such subjects as bear upon continental growth and intercontinental relations. It is proposed to make this a leading line of discussion during the Congress, in the belief that there is no subject more appropriate, and that there is none which better represents the present efforts of geologists or commands a more general interest. It is hoped that analytical maps will be prepared by the geologists of the several countries representing the stages of growth of these regions in each of the great eras from the Archean to the Pleistocene, and that such analytical maps may constitute a leading feature of the several presentations. Among the subjects upon which contributions are specially invited are the following: The correlation of continental and intercontinental orographic movements and geographic accretions by sedimentation; The coördination of periods of vulcanism in the different countries; The coördination of climatic states and changes; The correlation of faunal and floral variations and migrations. It is hoped that one session may be devoted to such coördination papers bearing upon each of the great subdivisions: viz., Archean, Paleozoic, Mesozoic, Cenozoic, and Pleistocene.

=Third.= Papers on Paleontological and Archeological Geology of international scope.

=Fourth.= Contributions to Physical, Structural and Petrological Geology having international or general bearings.

=Fifth.= Contributions to Economic Geology having general bearings.

=Sixth.= Miscellaneous papers of especial and general interest.

The foregoing groups are intended to embrace and coördinate the list of special themes announced in the circular issued by the local committee some months since, except such as may be best suited to popular presentation, for which special provision is to be made.

It will be determined later, when the number and nature of the papers are ascertained, whether all will be arranged so as to form a continuous program, or whether sub-sections will be formed and two or more sessions held simultaneously.

It is the desire of the World's Congress Auxiliary that a few addresses of a popular nature shall be given, with a view to stimulating an interest in the development of the science on the part of the public.

T. C. C.

Extra copies of the articles appearing under the head of Studies for Students will be printed and kept on sale for the use of teachers and advanced classes. The prices will be fixed as low as practicable, and a standing list published in the advertising columns of the =Journal=.

=_Reviews._=

_On the Glacial Succession in Europe._ By Prof. =James Geikie=.
Transactions of the Royal Society of Edinburgh, Vol. XXXVII.,
Part I. (No. 9), 1892, pp. 127-149 (with a map).

In this timely essay Prof. Geikie reaches the following conclusions:

1. The record of the first glacial epoch is found in the Weyborn Crag of Britain, and the ground moraine beneath the "Lower Diluvium" of the continent. During this epoch, the direction of the ice movement in southern Sweden was from the south-east to the northwest. This first glacial epoch of which direct evidence is adduced was followed by an interglacial interval, during which the forest-bed of Cromer, the breccia of Hötting, the lignites of Leffe and Pianico, and certain beds in central France were deposited. During this interglacial epoch, the climate is believed to have been very mild.

2. There followed a second epoch of glaciation, when the ice sheet of Britain became confluent with that of the continent. This was the epoch during which the ice sheet reached its southernmost extension. Its depositions are found in the lower boulder clays of Britain, the lower diluvium of Scandinavia and north Germany (in part), the lower glacial deposits of south Germany and central Russia, the ground moraines and high level gravel terraces of Alpine lands, and the terminal moraines of the outer zone. During this second glacial epoch, Alpine glaciers are believed to have attained their greatest development. This epoch of extreme glaciation was followed by an interglacial interval, during which Britain is believed to have been joined to the continent. During this interval, the climate became temperate. In Russia (near Moscow) there seems to be evidence that it was milder and more humid than that of the same region at the present day. Toward the close of the mild epoch, submergence seems to have been accompanied by an increasing degree of cold, which finally ended in another glacial epoch.

3. The subsidence which marked the close of the second interglacial interval, marked likewise the inauguration of the third glacial epoch. Its work is represented in Britain by the upper boulder clay, in Scandinavia and Germany by the lower diluvium (in part), in central Russia by the upper glacial series, in Alpine lands by ground moraines and gravel terraces. The ice sheets of Scandinavia and Britain were again confluent, but did not extend quite so far south as during the second glacial epoch. This third glacial epoch is believed to have been followed by another interglacial interval, during which fresh water alluvia, lignite and peat accumulations were made. These are represented by the interglacial beds of north Germany, and by some of the so-called post-glacial alluvia of Britain. There were also marine deposits on the coasts of Britain and on the borders of the Baltic. During this interglacial interval, Britain is believed to have been continental. The climate was temperate, but in the course of time became more severe. This increasing severity seems to have been accompanied by submergence, which amounted to something like 100 ft. below the present sea-level on the coasts of Scotland. The Baltic provinces of Germany were also invaded by the waters of the North Sea.

4. There followed a fourth period of glaciation, during which the major part of the Scottish Highland was covered by an ice sheet. Local ice sheets existed in the southern uplands of Scotland and in mountain districts in other parts of Britain, and the great valley glaciers sometimes coalesced on the low lands. Icebergs floated out at the mouths of some of the highland sea-lochs. In some places, terminal moraines were deposited upon marine beds which were then in process of formation. These beds are now 100 ft. above the sea level. At this time Scandinavia was covered by a great ice sheet, which yielded icebergs to the sea along the whole west coast of Norway. The ground moraines and terminal moraines of the mountain regions of Britain represent the deposits of this ice epoch. The upper diluvium of Scandinavia, Finland, and north Germany represent the work of the contemporaneous, but not confluent, ice sheet of the continent. In the Alps, terminal moraines in the large longitudinal valleys were made at the same time.

This fourth glacial epoch was followed by a fourth interglacial interval, during which fresh water alluvial deposits were made, and also the "lower buried forest and peat" of Britain and northwestern Europe. At this time, Scotland seems to have stood 45 to 50 feet lower than now, and Carse clays and raised beaches represent the work of the sea. During this interglacial interval, Britain is believed to have become again continental, while the climate became so far ameliorated as to allow the growth of great forests. Subsequently the insulation of Britain was effected, and this was followed by a climate which was probably colder than the present.

5. The severity of the climate which marked the close of the fourth interglacial interval was such as to bring about local glaciation in some of the mountain valleys of Britain. Here and there the glaciers projected their moraines so far down the mountains that they rest on what is now the 45 to 50 feet beach. In the Alps, this fifth epoch of glaciation is represented by the so-called post-glacial moraines in the upper valleys. This is believed to have been the last appearance of glaciers in Britain. The dissolution of these glaciers was again followed by an emergence of the island, and by more genial climatic conditions.

In support of his conclusions, Prof. Geikie cites some striking facts which are not so widely known as they should be. For example, Swedish geologists have found evidences that there was an ice sheet antedating that which deposited the "lower diluvium," and that during this earlier glaciation the direction of ice movement in southern Sweden was from the south-east to the north-west. The ground moraine deposited by this ice sheet is overlain by the "lower diluvium" which was produced by an ice movement from the north north-east to the south south-west, or nearly at right angles to the first. Again, near Moscow, there exist interglacial beds whose plant remains indicate a climate milder and more humid than that of the present time. These interglacial beds, it will be observed, occur in the region of the "lower diluvium" quite beyond the margin of the ice which produced the "upper diluvium" of Germany and Scandinavia. During this interglacial interval, Prof. Geikie maintains that no part of Russia could have been covered with ice. If, then, within the limits of the area covered by the "lower diluvium," and not by the "upper," distinct beds of glacial drift are separated by such beds as those cited, there can be no question but that such separation marks two distinct glacial epochs. If there was an earlier glaciation when the movement of the ice in Sweden was at right angles to that during which the lower part of the "lower diluvium" was produced, this also would seem to be good evidence of three ice epochs prior to the "upper diluvium." The epoch of the "upper diluvium" would then constitute the fourth glacial epoch, and this is the interpretation of Prof. Geikie.

Outside the area of the European continental ice sheet, facts are adduced in striking confirmation of the multiple ice epoch theory. These facts are found in Switzerland, where evidences of multiple glaciation have been recognized, and in the Pyrenees where evidences of three separate ice epochs have been found. In France, evidences of an interglacial interval have been found in the region of the Puy de Dôme of such duration as to allow the excavation of valleys to a depth of 900 feet. The length of time which would be required for such stupendous erosion must certainly be regarded as sufficient to allow the preceding and succeeding glaciations to be considered as belonging to two distinct epochs.

Another point of great significance and interest which Prof. Geikie's essay brings out, is the correlation in Britain between epochs of glaciation and epochs of subsidence on the one hand, and between interglacial intervals and epochs of elevation on the other. If Prof. Geikie's interpretation be well founded, and so far as we are able to judge from the facts presented this is the case, his conclusions would seem to be fatal to the hypothesis that glacial climate was produced by northern elevation.

The map which Prof. Geikie gives, showing the limit of ice advance during the fourth glacial epoch, seems to us open to criticism. On the ground of personal observation, the writer believes that the ice sheet of the glacial epoch here represented did not extend notably, if at all, beyond the Baltic Ridge.[18]

[18] See _American Journal of Science_, May, 1887. In a recent letter, Prof. Geikie indicates that he is convinced, from subsequent personal observation, that his map is erroneous so far as the limit of the ice of this epoch is concerned. The mapping given was based on the opinion of others.

Prof. Geikie is an advocate of Dr. Croll's astronomical theory of glacial climate, and thinks that even five is not the full number of glacial epochs belonging to the Pleistocene period. He believes there may have been a series of glacial epochs increasing in severity to a maximum represented by what is now designated as the second glacial epoch. This maximum was followed by a series of epochs of diminishing severity, represented by what he designates the third, fourth and fifth epochs. The essay is a timely contribution to glacial geology.

=Rollin D. Salisbury.=

=_Analytical Abstracts of Current Literature._=[19]

[19] Abstracts in this number are prepared by Henry B. Kummel, Chas. E. Peet, J. A. Bownocker.

_The Sub-Glacial Origin of Certain Eskers._ By =William Morris
Davis=, Harvard University. (Proceedings of the Boston Society
of Natural History, Vol. XXV., May 18, 1892).

A critical discussion of the conditions under which it is conceived certain eskers and sand plateaus (plains) were formed. The Auburndale district, ten miles east of Boston, presents three classes of modified drift deposits;--sand plateaus, eskers, and kames. These deposits are well exposed.

The sand plateaus have the characteristics of delta deposits of glacial streams,--even surfaces, well-bedded sands and gravels, the beds sloping outward from the "head" at an angle of 12° to 20°, and in close agreement with the slope of the plateau front, a lobate margin, deposits distinctly coarser at the head than near the front, and a series of nearly horizontal roughly cross-bedded gravels overlying the sloping beds.

The eskers are essentially of the same material as that of the plateau, often so poorly stratified as to render differentiation of the beds difficult. The interstices between the pebbles are often unfilled, although there is abundance of fine material in adjoining layers. This "open work" is taken to indicate rapid deposition, and seems to preclude the supposition that the gravels have settled down from a superglacial position, or been traversed by currents of any volume. In several instances the eskers can be followed to direct union with sand plateaus. Towards its lower end the esker frequently "gives out branches" and "the adjacent lowland surface becomes more or less encumbered with sand mounds or kames," indicating a decayed margin of the ice.

Prof. Davis' conclusions are:

"1. The eskers and sand plateaus of Auburndale and Newtonville were formed by running water just inside and outside of the ice margin in the closing stage of the last glacial epoch.

"2. The ice-sheet was a stagnant, decaying mass at the time of their formation, as is shown by the ragged outline of its margin.

"3. Eskers and sand plateaus are genetically connected; the term, feeding-esker, is fully warranted by the relation of the two in position, structure, and composition.

"4. The sand plateaus were made rapidly; this is proved by the absence of disordered beds at their heads, where space would have been opened by the backward melting of the ice had the forward growth of the plateau been slow. The eskers were also made rapidly, as is shown by their 'open-work gravels.'

"5. The diversion of the feeding streams to other outlets left the plateaus and the eskers without further energetic action as the ice melted away from them.

"6. The present form and structure of the eskers are more accordant with the supposition of a subglacial origin than of a superglacial origin; but it is not intended to imply that other eskers of more irregular form and different structure could not have been deposited in superglacial channels."

H. B. K.

* * * * *

_Studies in Structural Geology._ By =Bailey Willis=, U. S. Geol.
Surv. (Transactions of the American Institute of Mining
Engineers, June, 1892).

The paper aims "to present some of the results of observation of the geologists of the Appalachian division during the past three years on the subject of structural geology in the Appalachian province." The structural features are all of one type but of different phases, comprised in four great districts. 1) the district of close folding, 2) a district whose chief structural characteristic is cleavage, 3) a district of open folding, 4) a district of faulting and folding. The answer to the questions, Why did the strata bend in the district of open folding, and why did they break in the district of faulting, is that the thrust affected them according to their rigidity under their respective conditions of superincumbent load. "We know that load up to a certain point restrains fracture in material under thrust." In the district of open folding the Devonian limestone is the most rigid of the strata and "the one which would most effectively transmit the compressing thrust and would control the resulting structure." In the district of open folding this limestone was prevented from breaking and faulting by a load of superincumbent strata exerting a pressure of 10,000 to 23,000 pounds per square inch, while in the faulted district a load of 5,000 to 10,000 pounds per square inch permitted the strata to break and fault.

The answer to the question, Why did the compression affect this zone, is given. "It becomes apparent on study of sections that where compression raised a great arch there previously existed a bend from a nearly horizontal to a descending position in the principal stratum transmitting the thrust. Greater anticlines and synclines originated in upward and downward convexity of initial dips, due to unequal deposits of sediments which depress underlying strata in proportion to their weight. Such folds may be called original." The Pottsville, Mahanoy, Shamokin and Wyoming coal basins of Pennsylvania belong to this class.

Experiments have recently been carried on in the office of the United States Geological Survey reproducing the different forms of folding. The experiments differed from other experiments in that 1) the materials used to simulate the stratified rocks varied in consistency from brittle to plastic, according to the depth at which deformation is supposed to take place; 2) the compression was exerted under a movable load representing the weight of superincumbent strata; 3) the strata rested on a yielding base to simulate the condition of support of any arc of the earth's crust. The following are the conclusions from the experiments:

1. "When a thrust tangentially affects a stratified mass, it is transmitted in the direction of the strata, and by each stratum according to its inflexibility. At any bend the force is resolved into components, one radial, the other tangential to the dip beyond the bend; the radial component, if directed downward, tends to depress the stratum and displace its support.

2. "A thrust so resolved can only raise an anticline or arch which is strong enough to sustain the load lifted by its development; such an arch may be called competent; and since strength is a function of the proportions of a structure, it follows that, for a given stratum, the size of a competent anticline will vary inversely as the load; or for a given load the size will vary as the thickness of the effective stratum.

3. "The superincumbent load borne by a competent anticline is transferred to the supports of the arch at the points of inflection of the limbs.

4. "When a competent arch is raised by thrust from one side, the load transferred may so depress the resulting syncline further from the force that an initial dip will be produced in otherwise undisturbed strata; this dip will rise to a bend from which a new anticline may be developed. This anticline is a result of the first, and may be called 'subsequent' in distinction to original folds. Since subsequent folds are simply competent structures, their size will be determined by conditions of thickness and load, and for like conditions they should be equal; and they must, in consequence of conditions of development, be parallel to the original fold and to each other. An example of an original fold with its subsequent anticlines is the Nittany arch and the group of parallel anticlines which lie southeast of it, extending northeast from the Broad Top basin."

C. E. P.

* * * * *

_The Catskill Delta in the Post-Glacial Hudson Estuary._ By =William
Morris Davis=. (From the Proceedings of the Boston Society of
Natural History, Vol. XXV., 1891).

The post-Tertiary trenches of the Hudson and its tributaries are in the main filled with clay beds, which, covered by a thin deposit of sand, rise in terraces 130, 150, or even 180 feet above tide-water. These clays are the result of a late glacial or post-glacial submergence of the valley, but their upper surface does not indicate the amount of their submergence, as they are bottom deposits. Delta deposits made by the tributary streams, where they entered the Hudson estuary, would indicate the amount of submergence.

Such deposits are found on the Catskill a mile north of Cairo, and eroded remnants are traceable for three or four miles down stream. The surface is characterized by great numbers of water-worn stones up to fifteen or eighteen inches in diameter. The lobate margin, where present, is poorly defined. These deposits range from 290 feet (aneroid) above tide, up river, to 270 feet further down. One-tenth of a cubic mile of material seems to have been washed into the Catskill trench at the point of this delta between the time of the ice departure and the elevation of the land. Subsequent terracing has removed half that amount.

The course of the Catskill at Leeds, where it crosses a ledge of hard Corniferous limestone is probably of post-glacial superimposed origin, but the preglacial valley cannot be definitely fixed.

H. B. K.

* * * * *

_Geological Survey of Alabama.--Bulletin 4._ By =C. Willard Hayes=.
(Report of the Geology of Northeastern Alabama and Adjacent
Portions of Georgia and Tennessee).

This report covers an area of 5950 miles, two-thirds in Alabama. Topographically it falls into three divisions: 1) the Cumberland and other plateaus of the northwest; 2) in the center, anticlinal valleys--Browns and Wills, with the synclinal mountains--Sand and Lookout; 3) the monoclinal mountains, the "flatwoods" (Coosa shales) and the chert hills (Knox limestone) of the southeast. The drainage of the first is radial from the center of the plateau to the Tennessee; that of the second, once consequent upon the folded structure, is now adjusted to the strike of the soft beds.

The formations are Cambrian, Silurian, Devonian and Carboniferous. Total thickness is from 13,000 to 18,000 feet in the east, but decreases westward. Hard sandstones of the Carboniferous form the cappings of the plateaus and synclinal mountains. In the anticlinal and monoclinal valleys the Silurian and Cambrian appear. The rocks pass from the nearly horizontal beds of the plateau region, by narrow unsymmetrical anticlines with steeper dip on the northwest side, and by broad shallow synclines, to the complicated folds of the southeast. The axes of these latter folds dip more or less abruptly northward and southward, causing the ridges to assume zigzag courses. Synclines are often crossed by anticlines.

Thrust faults exist, some of great magnitude, and traceable for 200 to 300 miles. By the "Rome thrust fault" the Cambrian shales have been shoved four to five miles over upon the Carboniferous shales. Most of the overthrust strata have been worn away, but tongues of Cambrian shale still remain to all appearances lying conformably upon the Carboniferous strata. Transverse thrust faults terminate Gaylor's ridge, Dirt Seller Mountain, and Lookout Mountain on the south.

H. B. K.

* * * * *

_The Correlation of Moraines with Raised Beaches of Lake Erie._
By =Frank Leverett=, U. S. Geol. Surv. (Wisconsin Academy of
Science. Vol. VIII., 1891).

References have been made in Geological literature to the beaches of the eastern portion of the Lake Erie basin, but up to the time of Mr. Leverett's work none of the beaches had been completely traced. Mr. Gilbert had discovered that several of the raised beaches do not completely encircle Lake Erie, and supposed that their eastern termini represent the successive positions of the front of the continental glacier during its retreat northeastward across the Lake Erie basin. Mr. Leverett verifies this theory by demonstrating that certain moraines are the correlatives of the beaches. They are as follows:

I. The Van Wert or upper beach and its correlative moraine, the Blanchard ridge. II. The Leipsic or second beach and its correlative moraines. III. The Belmore, or third beach and its correlative moraine.

I. The Van Wert beach extends eastward from the former southwestward outlet of Lake Erie near Fort Wayne, Indiana, to Findlay, Ohio, where it joins the Blanchard moraine. Through Indiana and Ohio its altitude is quite uniformly 210 feet above Lake Erie.

While the Van Wert beach was forming, the ice front was the northeastern shore of the lake as far east as Findlay, Ohio, its position being marked by the Blanchard moraine. East of Findlay, where the Van Wert beach joins it, the moraine is of the normal type. But west of Findlay, it presents peculiarities of topography and structure, resulting from the presence of lake water beneath the ice margin. The water was shallow and incapable of buoying up the ice-sheet, and producing icebergs. The motion of the water under the ice-sheet produced a variable structure. This is the only instance of a moraine demonstrably formed in lake water.

II. The Leipsic, or second beach, was formed after the ice had retreated from its position marked by the Blanchard moraine. Its altitude is 195 to 200 feet above Lake Erie. It has its terminus near Cleveland, where it connects with the western end of a moraine.

III. The Belmore beach and its correlative moraine. Between the Leipsic beach and the present shore of Lake Erie are several beaches. One of these, the Belmore beach, terminates near Cleveland, while the others extend into southwestern New York, and probably connect with moraines, though this connection has not been traced. The general altitude of the Belmore beach in Ohio is 160 to 170 feet above Lake Erie. Unlike the Van Wert and Leipsic beaches, it does not directly connect with a moraine at its eastern end, but a gap of ten miles intervenes. Terraces at Cleveland, Mr. Leverett thinks, make a connection between the eastern end of the beach and the western end of the moraine at Euclid, Ohio.

C. E. P.

* * * * *

_The Climate of Europe During the Glacial Epoch._ By =Clement Reid=.
(Natural Science. Vol. I, No. 6, 1892).

_Temperature of the Sea._--The temperature of the English Channel was similar to that where the isotherm of 32° F. is now situated. The winter temperature can scarcely have been 20° colder than at present. The Mediterranean was perhaps 5° colder than now.

_Temperature of the Land (air)._--It does not appear that the climate of the lowlands of southern Europe can have been 20° lower than the present mean; 10° or perhaps less appear to have been the refrigeration in the Mediterranean region. The temperature at the southern margin of the ice-sheet was about 20° colder than at present. The temperature increased rapidly towards the south. Recent observations seem to show that throughout central Europe there was a period of _dry_ cold, causing the country to resemble the arid regions of central Asia.

J. A. B.

* * * * *

_On the Glacial Period and the Earth-Movement Hypothesis._ By
=James Geikie=, Edinburgh, Scotland. (Read before the Victoria
Institute, London).

Geologists generally admit that there have been at least two glacial epochs, separated by one well-marked interglacial period. The closing stage of the Pleistocene period was one of cold conditions in northwestern Europe, accompanied by land depressions. After this came a genial climate with a union of the British islands among themselves and also with the continent. This was followed by a cold, humid condition.

Upham maintains that the whole of North America north of the Gulf of Mexico stood at least three thousand feet higher at the beginning of the glacial epoch than at present. Fiords were formed before glacial times and so can not be cited as evidence of high land during the glacial period. An elevation of land in the northern part of North America and Europe could not produce glaciation in their southern parts. The deflection of the Gulf Stream by the sinking of the Panama, Professor Geikie argues, could not produce the conditions which prevailed during the glacial epoch. The Earth-Movement hypothesis, he believes, accounts neither for the widespread phenomena of the ice-age, nor for the remarkable interglacial climates. Some maintain that the warm interglacial period was produced by the rise of the Panama land, the sinking of the lands to the north, and the turning of the Gulf Stream from the Pacific into the Atlantic. Why then, asks Professor Geikie, do we not have such a climate now?

J. A. B.

=_Acknowledgments._=

The following papers have been donated to the library of the Geological Department of the University of Chicago, mainly by their authors:

=Abbe, Cleveland.=

--On the Production of Rain. 8 pp. 1892.

=Ami, Henry M.=, M.A., F.G.S.

--On Canadian Extinct Vertebrates. 4 pp.--Ottawa Naturalist.

--On the Geology of Quebec and Environs. 26 pp., 1 pl.--Bull. Geol.
Soc. Am., vol. 2, pp. 477-502.

--On the Geology of Quebec City, Canada. 4 pp.--Canadian Record Sci.,
April, 1891.

--Additional Notes on Ganiograptus Thureani, McCoy, from the Levis
Formation Canada. 2 pp.--Canad. Record Sci., Oct. 1889.

--Reviews of Reports and Papers on Canadian Geology and Paleontology.
8 pp.--Ottawa Naturalist, Oct.-Dec. 1892.

--Notes and Descriptions of some new or hitherto unrecorded species
of Fossils from the Cambro-Silurian (Ordovician) Rocks of the
Province of Quebec. 15 pp.--Canadian Record of Sci., April, 1892.

--Review of Catalogue of the Fossil Cephalopoda of the British
Museum, Part 8, Nautiloidea. By Arthur H. Foord, F.G.S. 3
pp.--Canadian Record of Sci., Sept. 1891.

--On the Sequence of Strata forming the Quebec Group of Logan and
Billings, with Remarks on the Fossil Remains found therein. 4
pp.--Ottawa Naturalist, June, 1892.

=Andeæ, A. and A. Osann.=

--Beiträge zur Geologie des Blattes Heidelberg. 39 pp., III., 2
pl.--Aus den Mittheilungen der Grossh. Badischen Geologischen
Landesanstalt, II Bd. VII-XI.

=Baltzer, A.=

--Beiträge zur Geognosie der Schweizer-Alpen über die Frage,
ob der Granit-Gneiss der nördlichen Gränzregion der
Finsteraarhorn-Centralmass eruptiv sei oder nicht, und über
damit zusammenhängende Probleme. 41 pp., 2 pl.--Neues Jahrbuch
für Mineralogie, 1878.

--Beiträge zur Geognosie der Schweizer-Alpen. Ueber die Marmorlager
am Nordrand des Finsteraarhorn-massivs. 20 pp., 2 pl.--Aus dem
Neuen Jahrbuch für Mineralogie, 1877.

--Ueber den Hautschild eines Rochen aus der marinen Molasse. 4 pp., 1
pl.--Aus den Mittheilungen der Naturforschenden Gesellschaft in
Bern.

--Ueber den natürlichen Verkohlungsprozess. 23 pp.--Aus der
Vierteljahrs-schrift der zürcherischen naturforschenden
Gesellschaft.

--Randerscheinungen der centralgranitischen Zone in Aarmassiv. 18
pp., 1 pl.--Aus dem Neuen Jahrbuch, 1885. II Band.

--Beiträge zur Geognosie der Schweizer-Alpen. Ein Beitrag zur
Kenntniss der Glarnerschlinge. 20 pp., 1 pl.--Aus dem Neuen
Jahrbuch für Mineralogie, Geol. und Pal. 1876.

--Geologische Skizze des Wetterhorns in Berner Oberland. 14 pp., 2
pl., Zeit. der Deut. geolog. Gesell, 1878.