196 W. UPHAM — MODIFIED DRIFT IN SAINT PAUL. 



englacial and superglacial position in and upon the melting ice-sheet. 

 It is an observation almost exactly like that made by me a year earlier 

 in the drift section of the lake Erie shore in Cleveland, Ohio;* and here, 

 as there, I conclude that the volume of the englacial drift is represented 

 by the thickness of the obscurely bedded or laminated till. 



Deflection of glacial Stride toward Lake Hamline. 



This is a second result of lake Hamline. Although the Trenton lime- 

 stone is extensively exposed in Saint Paul along the bluffs of the Missis- 

 sippi valley and on its terrace, these rock surfaces are almost everywhere 

 so deeply affected by weathering that they retain no glacial striae. Only 

 at one locality, on the south side of the river where the bluff is ascended 

 by Charlton street, a third of a mile east of the Smith Avenue or High 

 bridge, I found glacial striation in several spots, at and near the west end 

 of Isabel street, bearing south 10° to 25° east, with another and quite 

 different course of striation, partly on the same surfaces and also on 

 other spots, bearing north 65° to 75° west. 



In each of these sets of striae, which comprise the only courses observed, 

 we have good evidence that the whole thickness of 10 to 12 feet of till 

 which lies next above the striated Trenton limestone, forming the sur- 

 face of this slope, was englacial. During the greater part of the late 

 glaciation which brought this till from the northeast, the ice current here 

 doubtless passed southwesterly. When the vicissitudes of the glacial 

 melting and changed distribution of snowfall caused the ice from the 

 northwest to push back that from the northeast on thisbelt of contend- 

 ing currents, the base of the deflected ice moved south-southeastward, 

 here effacing all the earlier southwestward striation. 



A little later, however, the melting of the ice on the area of lake Ham- 

 line again deflected the ice current here, this time almost reversing it 

 and directing it toward the open lake area. The site of these striae is 

 opposite to the northeast end of the Summit Avenue plateau, the inter- 

 vening valley being a mile wide. 



In each instance of these deflections of the ice currents, the base of the 

 ice-sheet, more or less filled with englacial drift, rested directly on the 

 limestone which it striated. The till was then englacial and super- 

 glacial. It did not come to occupy its present position beneath the ice- 

 sheet, but after the ice in which it was contained had melted away. 



*Bull. Geol. Soc. Am., vol. vii, 1896, p 331. 



