214 SIXTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



Second sandstone 70 feet*. 



Third Magnesian limestone .... 350 " 



Third sandstone 60 " 



Fourth Magnesian limestone . . . 300 " 



"We look in vain, therefore, for that great development of are- 

 naceous sediments at this period, which we find farther to the 

 north in the Mississippi valleyf. 



Considering this great augmentation of magnesian limestone 

 towards the south, and the largely increased thickness of the 

 sandstone farther north, we might be prepared to expect the final 

 disappearance of the limestone in that direction, and of the sand- 

 stone to the southward. Now it happens that to the north of the 

 localities on the Upper Mississippi valley, we have, upon Lake 

 Superior, a great development of sandstone, the precise age of 

 which has for some time been debated, and from which no fossils 

 have been obtained, with the exception of a single species of 

 LingulaJ. 



In his Report for 1840, Dr. Houghton says : 



•* This Lake Superior sandstone, in its easterly prolongation, rests against 

 ** and upon the primary range of the Ste. Marie's river, before described > 

 " while on the south, it is seen to pass beneath the limestone at the Nebeesh 

 " rapids of the boat and canoe channels of that river. The rapids or falls 

 " of the Ste. Marie's river are formed by the passage of the waters over 

 '* the outcropping edge of the sandrock, which inclines or dips from this 

 ** point southerly ; thus passing conformably below the limestone before 

 " alluded to." 



So long since as 1845, I had myself observed that the sand- 

 stones of the St.Mary's river come out from beneath the Black- 

 river and Birdseye limestones ; but the Calciferous sandstone was 

 nowhere visible in the immediate neighborhood. The later and 

 more complete investigations of the Canada Geological Survey 

 have proved the absence of the Calciferous sandstone, and of the 



* Dr. Shumard has given this sandstone as attaining a thickness of one hundred and 

 twenty to one hundred and forty feet in some localities (Geological Report of Mis- 

 souri, p. 166). 



t If we take the First Magnesian limestone of Prof. Swallow as the representative 

 or equivalent of the Eastern Calciferous sandstone, it will not materially alter the 

 general conclusion; for we add but 125 feet of sandstone, with 190 feet of magnesian 

 limestone, above the beds just cited. 



t This LiNOULA I have formerly referred to L. prima of the Potsdam sandstone; 

 but a later critical examination of the specimens which have been more carefully 

 separated from the surrounding stone, shows it to be more nearly x'elated to a species 

 in the Calciferous sandstone. 



