August 17, 1SS3.] 



SCIENCE. 



199 



The only large continental area in tlie northern 

 lieniispliere supposed to be entirely ice- and snow-clad 

 is Greenland; and this, so far as it goes, is certainly a 

 local case, for the ice and snow of Greenland extend 

 to the south as far as 00° N. latitude, while both in 

 Norway and in the interior of North America the 

 climate in that latitude permits the growth of cereals. 

 Further, Grinnel Land, which is separated from 

 North Greenland only by a narrow sound, has a com- 

 paratively mild climate, and, as Nares has shown, is 

 covered with verdure in summer. Still further, Nor- 

 denskiold, one of the most experienced arctic explor- 

 ers, holds that it is probable that the interior of 

 Greenland is itself verdant in summer, and is at this 

 moment preparing to attempt to reach this interior 

 oasis. Nor is it difficult, with the aid of the facts cited 

 by WoeickofI and Whitney,' to perceive the cause of 

 the exceptional condition of Greenland. To give ice 

 and snow in large quantities, two conditions are re- 

 quired, — first, atmospheric humidity; and, seccmdiy, 

 cold precipitating regions. Both of the.se conditions 

 meet in Greenland. Its high coast-rangi'S receive 

 and condense the humidity from the sea on both 

 sides of it and to the south. Hence the vjvst accu- 

 mulation of its coiist snow-fields, and the intense 

 di-icliargc of the glaciers emptying out of its valleys. 

 AVhen extreme glaciaTists point to Greenland, and 

 ask us to believe that in the glacial age the whole 

 continent of North America as far south as the lati- 

 tude of 40° was covered with a continental glacier. 

 In some places several thousands of feet thick, we 

 may well .ask, first, what evidence tlieie is that Green- 

 land, or even the antarctic continent, at present shows 

 such a condition ; and, secondly, whether there exists 

 a possibility that the Interior of a great continent 

 could ever receive so large anara<mnt of precipiiatiiui 

 •as that required. So far as present knowledge exists, 

 it is certain that the meteorologist and the physicist 

 must answer both questions in the negative. In 

 short, iier|)etual snow and glaciers must be local, and 

 cannot be continental, because of the vast amount 

 of evaporation and condensation required. These 

 can only be possible where comparatively w.arm 

 se.is supply moisture to cold and elevated land; ami 

 this supply cannot, in the nature of things, penetrate 

 far iidaud. The actual condition of interior Asia 

 and interior America in the higher northern latitudes 

 affords positive proof of this. In a state of partial 

 submergence of our northern continents, we can 

 readily itnagine glaclation by the combined action of 

 local glaciers and great ice-floes: but, in whatever 

 way the phenomena of the bowlder clay and of the 

 so-called terminal moraines are to be .accounted fur, 

 the theory of a continuous continental glacier must 

 he given up. 



I cannot better indicate the general bearing of facts, 

 as they present themselves to my mind in connection 

 with this subject, than by referring to a paper by Dr. 

 6. M. Dawson on the distribution of drift over the 

 great Canadian plains east of the Kocky Mountains.'- 



> Memoir on iflaciers, Ocol. soc. Berlin, 1*81. Climatic 

 cliiinet'S, Iloi-inn, 18S3. 

 ■' Science, July 1, 1883. 



I am the more inclined to refer to this, because of iu 

 recency, and because I have .so often repeated similar 

 ronclusions ,as to eastern Canada and the region of 

 the Great Lakes. 



The great interior plain of western Canada, be- 

 tween the Laiu'eiitian axis on the e.ast and the IfocUy 

 Moiuitains ou the west, is seven hundred miles in 

 hre.idlh, and is covered with glacial drift, presenting 

 one of the greatest examples of this deposit in the 

 world. Proceeding eastward from the base of the 

 liiicky Mountains, the surface, at first more than 

 four thousand feet above the sea-level, descends by 

 successive steps to twenty-five hundred feet, and is 

 based on cretaceous and Laramie rocks, covered by 

 bowlder clay and sand, in some places from one hun- 

 dred to two hundred feet in depth, and filling up pre- 

 existing hollows, though itself sometimes piled into 

 ridges. Near the Kocky Mountains the bottom of 

 the drift consists of gravel not glaciated. This ex- 

 tends to about one hundred miles east of the moun- 

 tains, and must have been swept by water out of 

 their valleys. The bowlder clay resting on this de- 

 posit is largely made up of local debris, in so far as 

 its paste is concerned. It contains many glaciated 

 bowlders and stones from the Laurentian region to 

 the east, and also smaller pebbles from the Kocky 

 Jlountains; so that at the time of its formation there 

 must have been driftage of large stones for seven 

 hundred miles or more frpm the east, and of smaller 

 stones from a less distance on the west. Tlie former 

 kind of material extends to the base of the mountains, 

 anil to a height of more than four thousand feet. 

 One bowlder is mentioned as being forty-two by for- 

 ty by twenty feet in dimensions. The highest Lau- 

 rentian bowlders seen were at an elevation of forty-six 

 huiuired and sixty feet, on the base of the Rocky 

 Mountains. The bowlder clay, when thick, can be 

 seen to be rudely stratified, and at one place includes 

 beds of laminated clay with compressed peat, similar 

 to the'forest beds describeil by Worthen and Andrews 

 iu Illinois, and the so-called intcrglacial beds described 

 by Ulnde on Lake Otitario. The leaf-beds on the Ot- 

 tawa Kiver, and the drift-trunks found in the bowlder 

 clay of Manitoba, belong to the same category, and 

 indicate that throughout the glacial period there were 

 many forest oases far to the north. In the valleys of 

 the Kocky Mountains opening on these plains there 

 are evidences of large local gl.aciers now extinct, and 

 similar evidences exist on the Laurentian highlands 

 on the east. 



Perhaps the most remarkable feature of the region 

 is that immense series of ridges of drift piled against 

 an escarpment of Laramie and cretaceous rocks, at 

 an elevation of about twenty-five hundred feet, and 

 known as the ' Missouri coteau.' It is in some places 

 thirty miles broad and a hundred and eighty feet iu 

 height above the plain at its foot, .and extends north 

 and south for a great distance; being, in fact, the 

 northern extension of those great ridges of drift 

 which have been traced .south of the Great Lakes, 

 and through Pennsylvania and New Jersey, and which 

 figiue ou the geological maps as the edge of the con- 

 tinental ghicier, — an explanation obviously inappli- 



