1883.] NATURAL SCIENCES OP PHILADELPHIA. 47 



since it may reasonably be doubted whether there could ever have 

 been formed in the extreme North an accumulation of snow and 

 ice of a magnitude sutlicient to propel southward a glacier, with 

 an estimated thickness of several thousands of feet, to a distance 

 of hundreds of miles, and up mountain slopes to heights equaling 

 five or six thousand feet. The magnitude (as to height) to whii-h 

 such a snow accumulation may attain, will be dependent upon two 

 conditions — (I), the quantity of aqueous (snow ) precipitation, and 

 (2), the upper limit in the atmosphere reached by clouds. It is 

 well known that clouds, as a rule, rise highest in the regions of 

 highest temperature — the equntorial — where the vapor absorption 

 by the atmosphere is greatest, and where the planes of acpieous 

 condensation are most distantly removed from the earth's sur ace ; 

 and, likewise, they rise higher in summer than in winter. The 

 minimum rise will necessarily be in the extieme Noith (or South), 

 and during the period of grentest cold, or winter. High (discharge) 

 clouds are a rarit}' in the polar regions, and consequently piecipi- 

 tation will be mainly restricted to a comparatively low atmospheric 

 zone. Above this zone, which will mark the upper limit of the 

 " ice-cap," there can be but little snow accumulation. As a matter 

 of fact, the officers of various Arctic expeditions have repeatedly 

 noted that the high mountain-crests and elevations in the far North 

 were frequently devoid of a snow covering, and that there was but 

 very little precipitation, even over the low lands, during the winter, 

 heavy precipitations setting in only with the S[)ring months. The 

 highest snow-clad elevation in the region of greatest cold (the West), 

 in Greenland, appears to be Washington Land, with an estimated 

 height of six thousand feet, which gives rise to the great Humboldt 

 Grlacier, Although this peak is completely buried under a mantle 

 of snow (of undetermined thickness, however), it may j-et safely 

 be doubted whether snow of any great thickness (unless under a 

 much loarmer climate)^ could accumulate on a summit of much 

 greater elevation. If not, this elevation, in the opinion of the 

 speaker, was entirel}'^ inadequate to account for the southward 

 propulsion of a glacier to the extent required by geologists. 



Professor Lewis remarked that notwithstanding the difficulties 

 in a theoretical explanation, the fact of a great continuous glacier 

 at the time of maximum glaciation seemed clearly indicated, at 

 least in America, b}^ the numerous observations recently made. 

 He "described the extent of the glacier in America, as indicated 

 by its terminal moraine, and stated that the close similarity of its 

 phenomena at distaiit portions of its southern edge indicated a 

 continuous ice-sheet. The continuous motion of its upper portion 

 is shown by the uniform direction of glacial stria? upon elevated 

 points. Thus the S. W. direction of the stria; upon the mountain 

 tops of N. E. Penna., was identical with that upon the Overlook 

 Mountain of the Catskills, and of that upon the summits of the 

 Laurentians of Canada. The striae at lower elevations conformed 

 more or less to the valleys, and did «ot indicate the general move- 



