VVAKKEN I 1'IIA.M — DISTRIBUTION OF ENGLACIAL DRIFT. 14J 



examinations of other counties in the eastern and the southwestern parts of the 

 state gave three localities where the thickness of the englacial drift deposited at 



the time <il' linal recession of the latesl ice-sheel is very clearly displayed by its 

 stratigraphic relations and by the erosion of water-courses. They can be only 

 briefly noticed here, and the final reports of this survey may be referred to for 

 detailed descriptions of the facts observed, with the full interpretation of their 

 significance. The must eastern of these Idealities is a plain of englacial till LO to 20 

 feet thick, overlying sand ami gravel which were deposited from a previously 

 melted ice-sheet, upon a width of five miles and length of probably fifteen miles in 

 Chisago and Pine counties.* Another similar flat tract of till, 16 to is feet thick, 

 overlies earlier modified drift near New ITIm.f The third and must interesting 

 group of observations was at lakes Benton, Shaokatan, and Hendricks, adjacent to 

 the outermost or Altamont moraine on the < !oteau des Prairies. These lakes lie in 

 water-courses which were channelled in the superglacial drift and continue through 

 the moraine. A thickness of al least 40 feet of englacial and afterward superglacial 

 drift is thus proved to have existed close to the ice boundary, where it was form- 

 ing massive morainic accumulations.:!: 



Manitoba. — The great belt of modified drift which extends from St. Paul and 

 Minneapolis north-northwest ward by the sources of the Mississippi and Red rivers 

 to the Lake of the Woods and to Bird hill in Manitoba, seven miles northeast of 

 Winnipeg, proves that much drift was contained in the ice-sheet along that dis- 

 tance of 400 miles. Toward this belt glacial currents converged from the northeast 

 and from the west and northwest, bringing doubtless more englacial drift than its 

 average in other parts of the ice-sheet: lis amount at the osar called Bird hill 

 appears to have been aboul 40 feet.? 



Another area to which much englacial drift was broughl by convergenl ice cur- 

 rents is the region of Riding and Duck mountains and the upper part of the Assini- 

 boine basin, as is shown by the immense supply of modified drift contributed by 

 the retreating ice to the Lake Agassiz delta of the Assiniboine river. Probably 

 more than ten cubic miles of gravel and sand, besides much liner silt and clay, were 

 there washed away from the melting ice surface and swept into this glacial Iake.[| 



Ti: \i is or s< avi v Engl \< i \ i. I >i;i it. 



X< w England. — As an example of tracts know n to have verj thin englacial drift 



from their being well nigh destitute of any superficial deposits and consisting in 

 large part or almost wholly of bare rock, we may cite the bell of very rocky, broken 

 country a few miles north of Boston, from Salem, Marhlehead and Lynn this 

 tract, occupied by Archean granite, felsitesand diorite, extends westward to Stone- 



ham and Winchester, its western pari being known as the Middlesex fells. The 

 action of the ice-sheet here seems to have been to sweep away whatever materials 

 it could gather, leaving drift deposits only where they became ensconced in hol- 

 low-, and are thus shown to have been subglacial. 



* i Minn., vol ii. 1888, pp. U3-417. 



fGeologyof Minn . o.l. i. 1884, pp. 581, 582. 



Ibid I "I. i. pp. IS03 604, 

 g" Glacial Lake \ ■_■ ■ iz in Manitoba," (feol. Sitrve, ta, Annual Report, new series, vol. iv, 



foi I--- ->. pp 16 12E. 



/ 90E; Bull. Geol. Soc. lm., vol. 2, 1890, pp. 272-274, 



