WARREN UPHAM — DISTRIBUTION OF ENGLACIAL DRIFT. 139 



is afforded by the Malaspina glacier, with its drift-covered tracts occupying a width 

 of about five miles on its seaward border, bearing flowering plants and even forest 

 trees ; and by the large rivers of t lie associated alpine glaciers, one of which emerges 

 from an ice-tunnel, flows for about Id miles in a channel open to the sunlight, 

 walled by ice and having ice beneath it, and then enters the mouth of another 

 tunnel and disappears* 



Though the ice-sheet of Greenland has formerly been more extended and deeper 

 than now. as is shown by glaciation of the rock surface high up on the sides of the 

 fjords, it has probably during several centuries been on the increase. There van be 

 little doubt that the climate at present is prevailingly colder than during the 

 prosperous period of the Norse colonies, between 900 and 500 years ago. By its 

 increasing accumulation, therefore, we may account for the contrast between the 

 Greenland ice, which has so little englacial and superglacial drift even near its 

 edge, and the partially drift-buried Malaspina -lacier in Alaska ; for there, accord- 

 in- to Russell, the ice has probably been on the wane during the past 500 or 1,000 

 years and at present is somewhat rapidly receding. Greenland is a picture of the 

 last glacial epoch at its culmination ; Alaska, of the Champlain epoch, of the final 

 melting of the ice-sheet and deposition of its englacial drift. The continuation of 

 these researches, now being prosecuted by Robert E. Peary and by Russell, 

 may be expected, therefore, to bring much further light on the history of North 

 America and Europe in the Pleistocene period. 



Tracts of abundant Englacial Drift. 



New England.— In Maine the maximum depth of the till is stated by Professor 

 ( ieorge H. Stone to be about 100 feet. Over the areas of clay slates he doubts that 

 its average depth is greater than ten feet, but in some granitic regions it appears 

 to average 50 or perhaps even 70 feet in thickness. The average over the whole. 

 of Maine is estimated by Stone to he probably between •'!(> and 50 feet. t A con- 

 siderable fraction of this, not less than a tenth and perhaps as much as a fifth, 

 must have been enclosed in the ice at the time of its final melting; for the abun- 

 dant osars, kames, valley drift, marine clays, and deltas of sand and gravel, which 

 tins author has so well described.;: were derived by water transportation from 

 the englacial drift, and doubtless much besides remained to be dropped on the 

 surface as the upper part of the till. 



In New Hampshire, which includes the most mountainous portion of New 

 England, after several years of work on the state geological survey, I estimated 

 the average thickness of the part of the till finally supplied from englacial drift to 

 be between three and four feet, this being the mean of sixty carefully observed 



sections; and the modified drift, which was also englacial, has nearly the same 



volume. The whole of the englacial drift in this state was therefore approx- 

 imately equal to a sheet seven feel thick.? To this we must probablyadd 1- or 15 

 feet for the mean depth of subglacial deposits of till (which I now think that I 

 then underestimated I, gh ing aboul •_'<» feel in total for the average thickness of all 

 the d rift, [n the White mountains and in very hilly districts the amount of drifl 

 is usually less than the average, many areas being mainly hair rock ; hut in a few 



*" An Expedition to Mount St Elias," pp LOO-112,185 I 

 ; Proceedings of the Portland Society oi Natural History, Nov. 21, 1881 

 ! Am. Jour, s.i., :;,| series, \>>l xl. L890. pp. 122 l 1 1. 

 I ■ ology of N. II., \..l. ni, ^7s, pp, -Jiil, 292. 



