ENGLACIAL TRANSPORTATION OF DRIFT. 195 



covered on its border by its formerly englacial drift. The converging 

 streams from the melting ice-fields on the east, north, and northwest 

 spread in these plateaus approximately a tenth of a cubic mile of gravel 

 and sand. No traces of subglacial stream courses are found from which 

 this modified drift could have been partly or wholly brought to its tracts 

 of thick deposition in the glacial lake ; bat instead, in two places, east of 

 the Hamline plateau and northeast of the Como plateau, eskers were 

 deposited at and near the mouths of the ice-walled rivers descending 

 from the drift-strewn surface of the attenuated and rapidly melting 

 marginal part of the ice sheet. 



It is thus indicated that much of the drift was transported in the lower 

 part of the vast continental glacier, and that, when its final melting had 

 reduced the thickness near the border to a few hundred feet, the ice there 

 became drift-covered, like the Malaspina glacier. Because the ice-sheet 

 and local glaciers of Greenland have recently been mainly increasing or 

 remaining nearly stationary, instead of rapidly receding, as in Alaska, 

 the englacial drift of Greenland fills only the lower third or half of the 

 steep frontal ice-cliffs, 100 to 200 feet high. Nearly the same proportional 

 height of transportation of englacial drift was probably the condition of 

 the North American ice- sheet on its peripheral areas to a width of several 

 hundred miles from the margin of its maximum extension. Above the 

 city of Saint Paul the ice-sheet probably attained a maximum thickness 

 of 2,000 feet or more, so that the upper limits of its englacial drift would 

 have been not less than 600 to 1,000 feet above the land surface. 



We may further remark, also, that the volume of the englacial drift on 

 areas of confluent ice currents, as the belt before mentioned extending 

 from Saint Paul northward across Minnesota, was much greater than on 

 other areas. Exceptionally abundant deposits of modified drift charac- 

 terize this belt throughout the state. 



Lacustrine Modification of englacial Till. 



Two other observations of results due to lake Hamline deserve brief 

 mention in closing this paper. One is an imperfect stratification seen in 

 the till. It is exposed to a depth of 20 to 25 feet, at an elevation of about 

 875 to 900 feet above the sea, in an excavation for the construction of a 

 road on the slope rising southward from the Mississippi river, in the west 

 part of section 13, Mendota. This exposure is a short distance east of a 

 bridge spanning a deep ravine, and the locality is opposite to the south- 

 west extremity of the Summit Avenue plateau, the width of the valley 

 between being one and a half miles. The modification of the till I at- 

 tribute to the action of the lake water in receiving it from a previously 



