GLACIAL INVESTIGATION IN xMlNNESOTA IN 1911 735 



off by the rasping ice. Tliese fresher drift materials were carried forward 

 in the ice-sheet to attain even higher levels than the older decayed drift At 

 the final melting snch fresh drift on some areas was deposited as "a thin 

 veneer," to use Mr. Leverett's words, upon the older general drift sheet and 

 on its accumulations in the great marginal moraines, all these diverse types 

 of the drift being laid down at the time of the melting away of the ice-sheet 

 The most remarkable contrast between Mr. Leverett's views and mine comes 

 in his assertion that our grand moraines of northern Minnesota were amassed 

 during a stage of glaciation wholly antedating the existence of Lake Agassiz, 

 and that a relatively late ice accumulation and readvance spread over these 

 abundant, steep, and high morainic hills without smoothing them down, 

 depositing upon them a veneer of the latest fresh gray till. The late lobe of 

 the ice-sheet stretched southward from the Red River valley to the vicinity 

 of Des Moines, in central Iowa, and its departure was attended by the glacial 

 Lake Agassiz, growing gradually north to the sites of Lake Winnipeg and the 

 Saskatchewan River. Differing from Mr. Leverett, I feel sure that our mas- 

 sive Minnesota moraines were formed contemiwraneously with the existence 

 of the great glacial lake and with its gradual extension northward, and my 

 opinion is that his veneering of fresh gray drift is merely the highest part of 

 the englacial drift, massed on the moraines at practically the same time with 

 their formation in the main part from lower and older englacial drift. 



Mr. Leverett, in reply, said : The suggestion made by Mr. Tyrrell, that 

 south west ward-bearing strife in eastern Manitoba indicate that the latest ice- 

 movement was from the northeast, is perhaps a correct one for that region. 

 But in northern Minnesota the strife with a southwestward bearing appar- 

 ently pertain to the ice-movement that deposited the red drift. The ice which 

 later came in from the northwest and deposited gray till over the red drift 

 did not efface all the stria^ of the earlier movement. This probably was due 

 to the slight abrasive power of the clayey drift material which it carried. 



GROOVED AND STRIATED CONTACT PLANE BETWEEN THE NEBRA8KAN AND 



KAN8AN DRIFTS 



BY J. EENEST CARMAN* 



The paper describes the unique feature of a grooved and striated contact 

 plane between the Nebraska (pre-Kansan) and Kansan drifts. Both sides 

 of the contact plane are striated. Neither side is the mold of the other. 

 The possible explanations are considered and the conclusion reached that 

 glaciation produced the feature. 



NEBRA8KAN DRIFT OF THE LITTLE SIOUX VALLEY IN NORTHWEST IOWA 



BY J. ERNEST CARMAN* 



The paper traces a farther extension of the Nebraskan drift and compares 

 the Nebraskan and Aftonian deposits of this region with those along the Mis- 

 souri River. 



3 Introduced by Georire F. Kay. 

 * Introduced by George F. Kay. 



