* 



O F L A K E SUPBRIO R. 



193 



of granite, exhibit the same deep red, ferruginous appearance, as the Lake Superior 

 sandstones. More quartzose, indeed, these usually are, some being true ferruginous 

 quartzites ; but still, in their general character, more nearly allied to the Lake Su- 

 perior rocks, than to the white and buff beds, to which, in the descending order, 

 they succeed. 



I am further of opinion, that the red sandstones of Lake Superior, in Wisconsin 

 and Minnesota, are but a continuation of the same ferruginous, argillaceous variety, 

 greatly expanded in thickness, which rises to view on the Upper St. Croix, and owes 

 its peculiarity to some local, modifying cause, perhaps to the influence of ferrugi- 

 nous waters, brought into action in a district of country that has been evidently 

 subjected, throughout a long period of time, to repeated volcanic eruptions, and of 

 which the structure indicates the frequent presence of iron ; and that they, with 

 their associated slates and conglomerates, form the lowest sedimentary strata, 

 throughout this entire region of country. 



If this be the true age of these rocks, it cannot surprise us, that they should have 

 been searched in vain for characteristic fossils. The absence of such fossils is a 

 strong argument in favour of the opinion which places them below the palaeozoic 

 base of the Mississippi Valley. It would not be easy to find, either in the Old Red, 

 the New Red, or the Upper Silurian Period, beds of red sandstone, attaining, as the 

 sandstones of Lake Superior doubtless do, to a thickness of more than five thousand 

 feet, and which have proved, throughout the whole of that thickness, so nearly 

 azoic. 



In accordance with the views herein expressed, I have, on the final Geological 

 Chart of this District, given to these sandstones, at the various points where they 

 are seen emerging from beneath the concealing drift, and other superficial deposits, 

 the chrome-yellow colour employed to designate F. 1. The superficial red marls 

 and clays, which engross so much of the surface of the southern shore, covering up 

 alike the thick masses of sandstone, with their associated rocks, and in part the 

 igneous protrusions also, are coloured of a pale red tint. 



TILTED STRATA OF RED SANDSTONE, LAKE SUPERIOR. 



25 



