STEUCTUEB AND STRATIGRAPHY, 29 



and probably the entire Crystal Falls district, was covered by Cambrian 

 ■deposits. The thickness of the Cambrian deposits can not be determined. 



The next higher portion of the geological time scale represented in the 

 district is that part of the Pleistocene period which in this part of the 

 United States is characterized by the jjast existence of great ice-sheets. 

 The evidences of the existence of the ice are everywhere present, either in 

 the rounding and polishing and scoring on the surfaces of the rocks 

 ■exposed or in the character of the drift deposits. The direction of the ice 

 movemei:it was clearly from the northeast to the southwest, as is shown by 

 the trend of the strife, which were observed upon the rounded rock out- 

 crops in various places. The thickness of the drift deposit varies very 

 materially. In places it has been almost entirely removed by denudation, 

 if in such places it ever formed anything more than a thin veneer upon the 

 surface. In other places it reaches a ver}- considerable thickness, as is 

 shown by the glacial topography characteristically developed in T. 45 N., 

 R. 32 W. 



As the present report is confined to the pre-Paleozoic rocks, no detail 

 description will be given of these Cambrian and Glacial deposits, nor are 

 they represented on the map, except in those places where it has been found 

 impossible to map the underlying rocks. The generalized columnar section 

 on PI. VII gives in condensed form our knowledge concerning the formations 

 mentioned. 



PHYSIOGRAPHY. 



TOPOGRAPHY. 



The topography in its large featui'es is pre-Glacial, and in some cases 

 this older topography is rather distinct. For instance, in the case of the 

 Deer River Valley, drift covers the gentle slopes and bottom, but is not 

 sufficiently deep to completely hide the pre-Glacial Deer River Valley. 



In the southwestern part of the district west of Crystal Falls, or, more 

 generally, west of the Paint River, pre-Glacial topography is seen in places. 

 Here we find the drift as a veneer and only partly hiding the bed-rock 

 topography, which depends mainly on the strikes, dips, and varying charac- 

 ters of the rocks. 



It is so well known that this part of the country was at one tune 

 -covered by ice, that it is useless to cite such proof as the rounding and 



