THE CENTEAL KEGION OP NOETH AMEEICA. 623 



Prof. N. H. Winchell, in an article in the ' Popular Science 

 Monthly ' for June 1873, entitled " The Drift Deposits of the North- 

 west," broadly accounts for the glacial phenomena on the supposi- 

 tion of a polar glacier. His illustrations are chiefly borrowed from 

 a careful study of the region south of the Great Lakes of the St. 

 Laurence; but as he includes the Valley of the Red River and the 

 entire North-west in his deductions, a brief note may not be inap- 

 propriate. The most suggestive portion of the paper is that in 

 which, like Mr. Belt, he traces the necessary production of a great 

 inland lake or sea of fresh water while the foot of such an ice-sheet 

 as that supposed gradually retreats towards the north, down the 

 gentle inclined plane of the surface of the country. In this manner 

 the finer stratified deposits of certain regions south of the Great 

 Lakes are accounted for, and also those of the great valley south of 

 Lake Winnipeg. 



Ingenious as this hypothesis of a great glacial lake undoubtedly is, 

 its inapplicability to the phenomena and physical features presented 

 by the region under consideration is at once apparent. In addition 

 to what has already been said, I need perhaps mention but one addi- 

 tional circumstance which appears discordant with it. 



From the physical geography of the region it will be evident that 

 the entire drainage of the supposed immense lake must have passed 

 southward by the Red-River valley. There is here no range of 

 mountains to be crossed ; and no reason can be assigned why a chan- 

 nel once formed should not have been cut down through the gentle 

 swell of the watershed and remained the permanent, as it appears 

 to have been the primitive, exit of the drainage of the country. 



The whole question is a very interesting one ; and it would seem 

 probable that the solution once arrived at will be found to apply 

 equally to Northern America and Northern Asia. 



EXPLANATION OF PLATE XXXII. 



Fig. 1. Map of part of the interior region of North America, showing the water- 

 sheds and three primary levels of the plains, the general character of 

 the drift, and the Missouri Coteau. a. The Drift plateau of Northern 

 Minnesota, with drift chiefly of northern and north-eastern origin. 

 h. Lowest prairie-level and valley of the Red River, c. Second prairie- 

 plateau}, drift derived chiefly from the east and north-east. d. Third or 

 highest prairie-plateau, drift chiefly composed of quartzite from the 

 Rocky Mountains, x. z. Missouri Coteau. 

 2. General section along the 49th parallel from the Rocky Mountains to 

 the Laurentian axis. Vertical scale much exaggerated, a, b, c, d x, 

 and z as in fig. 1. y. Turtle Mountain. 



a. J. G. S. No. 124. 2 t 



