430 W. UPHAM — ESKER NEAR WINNIPEG, MANITOBA 



valle}^, the amount of lacustrine sedimentation appears to have been 

 slight and even negligible, excepting on areas of deltas where the lake 

 received tributary streams laden with modified drift. Most of the strati- 

 fied clay and silt along the axial lowest part of the valley, as about Birds 

 Hill, seems therefore referable to alluvial deposition by river floods after 

 the glacial lake had been drained away. Both lake sediments and river 

 alluvium are absent from the tracts of till, indicating there for the till 

 alone a probable thickness of 50 or 60 feet. On other areas, where the 

 alluvium is deep, as generally along the central part of the valley, quite 

 probably the underlying till averages likewise some 50 feet in thickness, 

 nearly all of which, according to the evidence afforded by Birds Hill, 

 was englacial and finally superglacial. 



The distance from Birds Hill to the boundary of the glacial drift is 

 about 700 miles to the south and 300 miles to the southwest. It may 

 be estimated, from altitudes of the drift on the White Mountains, the 

 Catskills, and the Adirondacks, that the ice-sheet similarly rising over 

 Manitoba attained a maximum thickness of at least one mile, or more 

 probably one and a half miles, about 8,000 feet. The gradients of its 

 surface were similar to the slowly ascending slopes by which the ice- 

 sheets of Greenland and the Antarctic Continent rise to altitudes of about 

 2 miles above the sea. In the lower quarter or sixth part of the ice 

 covering Manitoba — that is, to a height of probably 1,500 feet — much 

 drift had been carried by its variable and partly rising currents. 



Near the border of the ice-sheet during its time of accumulation, little 

 drift could thus be carried into it, and therefore in the melting and re- 

 cession of that outer part the englacial drift was generally inconspicuous ; 

 but at any considerable distance within the glaciated area, as a score of 

 miles or more, the final melting set free much formerly englacial till and 

 modified drift. Failure to recognize the origin of these deposits in New 

 England has led a recent investigator of its glacial history to add, 

 erroneously, as the present writer thinks, a late and distinct stage of 

 glaciation to account for what seems to me an envelope or mantle of 

 englacial drift spread over that region.'' 



The processes of drift transportation and deposition here emphasized 

 were well stated by Prof. N. H. Winchell in 1873,« by Prof. C. H. Hitch- 

 cock in 1878,^ and by me in 1876 and 1878 and in numerous later 



5 Frederick G. Clapp : Complexity of the Glacial Period In northeastern New England. 

 Bull. Geol. Soc. Am., vol. 18, pp. nO.'=i-556, with plates 57-60. February 20. 1908. 



" The drift denosits of the northwest. Popular Science Monthly, vol. HI, pp. 202-210. 

 286-297 (especially page 294, relating to superglacial drift). 



7 Geology of New Hampshire, vol. lii, pp. 282, 283, 309, 326, 333-338. 



