April 14, 1898] 



NATURE 



■571 



by Mr. Owens's excavation. The disjointed stones of the 

 upper part of the stairway (some of which have already been 

 cleared away) had slid down bodily from above and, until the 

 excavation was made, had completely hidden the lower part of 

 the stairway. 



It is to be hoped that the next part of the Memoirs of the 

 Peabody Institute will give the details of this interesting work, 

 and a more accurate (if less ambitious) drawing than that of the 

 " restored " stairway published in the Century Magazine. If 

 it has been possible to preserve the continuity of the inscription 

 on the steps, Mr. Gordon's labours will have added to our store 

 one of the longest and most valuable inscriptions yet found in 

 Central America. 



Surely it is through an unintentional error that the drawing 

 of the Jaguar stairway, on page 409 of the Century, is ascribed 

 to Henry Sandham. A. P. M. 



RECENT PAPERS ON GLACIATION. 



A T the Toronto meeting of the British Association the 

 •^*- numerous papers bearing on the glaciation of the North 

 American continent were of exceptional interest to the British 

 student of glacial geology, inasmuch as they brought pro- 

 minently to mind the methods adopted by the Canadian and 

 American glacialists, which differ in many respects from those 

 to which we have become accustomed on this side of the 

 Atlantic. 



In no branch of earth-lore is the influence of his environment 

 more strongly impressed upon the worker than in stratigraphical 

 geology, and the effect of the simple topographical forms and of 

 the enormous extent over which the glacial deposits are distributed 

 in North America, has been to give a broader grasp and bolder 

 tone to the general run of its glacial literature. This was admir- 

 ably illustrated by the work brought forward at the meeting. In 

 the British Islands, from the abundance of natural and artificial 

 sections as well as from the complexity and narrow limits of 

 the topography, the lithological composition of the drift 

 deposits is usually made the pivot of the studies, while in 

 America it is rather the arrangement of the drift in regard to 

 the general phy.sical features which is held to be of paramount 

 import. 



The following comments on the papers read at Toronto have 

 been written from the standpoint of a ^itish glacialist anxious 

 to find wherein he might profit by the adoption at home of the 

 Transatlantic methods. 



To realise the extent of the field in North America it must be 

 remembered that the total area of the Dominion of Canada, 

 about 3,616,000 square miles or not much less than the 

 whole of Europe, can show, in one form or another, traces of 

 the Great Ice Age in every part, and that the same glaciated 

 area further extends over a region about one-fifth as large to the 

 southward of the Canadian border. It is not surprising, then, 

 that the study of glacial phenomena should have attracted so 

 many able workers in Canada and the United States. 



The exploratory work of Russell, Wright and others upon the 

 existing glaciers of Alaska, and of Chamberlin, Peary, Barton 

 and others upon the edge of the ice-sheet in Greenland has been 

 more readily assimilated by American than by British glacialists, 

 and its influence is perceptible throughout their researches. It 

 is true that the Danish explorers had already made known to us 

 the leading facts relating to the latter region, but their studies 

 were not perhaps made so directly from the standpoint of the 

 glacial geologist as those of the above-mentioned observers, nor 

 were their results so accessible to the English-speaking geologists. 

 But since Russell, by his investigation of the Malaspina Glacier, 

 with its forested moraine covered margin sheltering a varied 

 fauna and flora, has shown how widely different are the con- 

 ditions of Piedmont ice and Alpine glaciers, and since Cham- 

 berlin, in describing the mode of occurrence of the detrital matter 

 in the basal layers of Greenland ice- tongues, has thrown so much 

 new light on the whole question of drift-deposition, the British 

 glacialist would do well to recognise, with his colleagues across 

 the Atlantic, that the glaciers of the Alps do not afford the best 

 introduction to the study of glacial geology. It is clear that 

 the Alpine conditions are, in many respects, very different from 

 those under which the ice-sheets of the Glacial period did 

 their work. 



As regards the cause of the Great Ice Age, we heard at the 

 Toronto meeting two interesting communications. That of Prof. 



NO. 1485, VOL. 57] 



T. C. Chamberlin, outlined in a former number of Nature 

 (September 16), was avowedly altogether speculative, and be- 

 longed to the domain of earth-physics rather than to geology in 

 the ordinary sense. The other was that in which Dr. J. W. 

 Spencer ably advocated his well-known views on the continental 

 elevation of the Glacial epoch. 



Dr. Spencer described a large number of drowned valleys, 

 often extending from the mouths of the great modern rivers across 

 the submarine plateaus at various depths, reaching to even 12,000 

 feet or more, and recognisable as far northward as Labrador. 

 He stated that upon tracing northward the deposits occupying 

 the great valleys, he found that glacial accumulations occur in 

 New Jersey between the Lafayette formation, which is the latest 

 horizon dissected by the great valleys, provisionally regarded as 

 of late Pliocene age, and the Columbia formation, which is mid- 

 Pleistocene. From all these considerations he concluded that 

 the eastern portion of North America stood more than two miles 

 above the sea during the earlier Pleistocene epoch. 



On other evidence he judged that the Mexican plateau was 

 mostly depressed to near sea level during the times of the high 

 elevation of the eastern portion of the continent ; and that, with 

 the subsidence of the eastern region, the western side of the 

 continent was elevated from 6000 to 10,000 feet or more. The 

 separation of the Atlantic and Pacific Oceans he regards as only 

 of recent date. These changes of levels and the dependent 

 variations of currents, &c., seem, in his opinion, to be sufficient 

 cause for the Glacial period. 



As Dr. Spencer pointed out, his views are practically those 

 which have been advocated by Lyell and many others. But 

 while a pre-glacial elevation of the North American continent is 

 generally acknowledged by geologists, the extent of this eleva- 

 tion is not usually admitted to have been even approximately as 

 large as Dr. Spencer would claim, and the difficulties in account- 

 ing for the widespread glaciation of the Northern Hemisphere 

 by the effects of elevation alone are so great that the defenders of 

 this hypothesis are at present few. 



There is a somewhat remarkable blank in the evidence to hand 

 in North America as to the conditions immediately antecedent 

 to the Glacial Period, nothing equivalent to the Forest Bed 

 Series and associated pre-glacial deposits, of which we possess 

 such excellent sections on our Norfolk coast, having yet been dis- 

 covered. For this reason the paper of Mr. R. Chalmers, of the 

 Geological Survey of Canada, on the pre-glacial decay of rocks 

 in Eastern Canada, was of especial interest. Mr. Chalmers 

 showed that in the region he described, beds of decomposed rock, 

 of variable thickness and more or less modified, occur wherever 

 the surface of the rocks has not been abraded by Pleistocene ice, 

 though boulder clay may often be found overlying them. 



He gave the following general section of these beds in descend- 

 ing order:— (i) Transported and stratified water- worn gravel 

 with beds of fine sand and clay. (,2) Coarse stratified gravels, 

 usually yellow and oxidised, the materials wholly local. (3) 

 Sedentary rotted rock, passing into solid rock beneath. 



There seems at present to be no evidence as to the precise 

 age of these beds in Eastern Canada ; but Mr. Chalmers 

 pointed out that somewhat similar deposits occurring at the 

 western base of the Green Mountains in Vermont, have yielded 

 vegetable remains by which Lequereux, many years ago, 

 referred them to the Miocene. He concludes that the general 

 aspect of the dry land in Eastern Canada previous to the 

 Glacial period must have been nearly similar to that of the 

 region .south of the glaciated zone in North America. 



The occurrence of similar local rubble in sheltered situations 

 beneath the drift has often been noted in the British Islands, and 

 the ease with which such loose-lying material would become 

 incorporated into the basal layers of an advancing ice-sheet has 

 been frequently discussed. On both sides of the Atlantic it 

 seems more probable that the greater bulk of the glacial 

 deposits was derived from this source, rather than from the 

 direct erosive action of the ice upon the solid rocks. 



With regard to the initial stages of the glaciation, while the 

 European glacialist looks to the highest ground in the* northern 

 part of his continent and its islands — to the mountains of 

 Scandinavia, of Scotland, England, Wales and Ireland, and of 

 Switzerland — as the great gathering grounds, it is generally 

 recognised that in North America, with the exception of the 

 Cordilleran mass in the extreme west, the glaciation commenced 

 and spread from the comparatively low ground in the north of 

 the continent and moved southward against the slope of the 

 land, the mountains near its south-eastern margin being 



