GGNTRIBUTIONS TO PALAEONTOLOGY. 217 



exposed along its shores should be so destitute of fossils ; while 

 we find equal difficulty in accounting for the sudden augmentation 

 and difference of character of the St. Peters sandstone of Wis- 

 consin, if we conclude the Lake Superior formations to be the 

 same or equivalent beds. This difficulty, however, is not greater 

 than we have in identifying the lower sandstone of the Mississippi 

 valley with the thin formation in Missouri and elsewhere. 



We have at Trempaleau and in the vicinity of Lake Pepin, 

 together with what we find on the Black and Chippewa rivers, 

 something like five (perhaps six) hundred feet of sandstone below 

 the Lower Magnesian limestone; while in Missouri its onlv known 

 representative in kind are the two beds of sandstone already 

 noticed, alternating with massive formations of magnesian lime- 

 stone, and together having a thickness of one hundred aud twenty 

 feet. The actual thickness of the sandstone in the northern lo- 

 calities cited is not known, but it is presumed to be much more 

 than that which is exposed above the river-level : the entire 

 thickness is probably not less than eight hundred feet, and perhaps 

 much more. This- mass, therefore, is apparently represented by 

 one hundred and twei"kty feet of sandstone in Missouri; and this 

 is divided into two bands, which may represent two of the epochs 

 noticed in the northern localities, as indicated by the fossils of 

 the Upper Mississippi valley. 



Regarding, for the present, the formations below the St.Peters 

 or Saccharoidal sandstone in Missouri as equivalent in age with 

 those of Wisconsin, we are compelled to recognize the Third and 

 Fourth Magnesian limestones of the Missouri Reports (as well as 

 the Second and Third sandstones) as represented in the sequence 

 by the sandstone of the Upper Mississippi river*. 



The material of this older sandstone has doubtless been derived 

 from the crystalline quartzose rocks of the Iluronian period, and 

 which are still exposed in extensive masses on the southern side 

 of Lake Superior, rising from beneath that formation. 



Taking this view of its origin, we are, in the region of the 

 Upper Mississippi, not far from its source ; and the older con- 

 glomerates at the base of the sandstone in the central part of 

 W^isconsin, which are similar to some of those on the south shore 



* The fossils described from the Third Magnesian limestone by Dr. Siiumard do 

 not, I believe, include any Trilobites; but all the species bear more analogy with those 

 known in the Calciferous sandstonn of New-York and of Canada, and Dr. Shumard 

 regards this rock as of the age of the lower magnesian limestone of Iowa, TVisconsia 

 and Minnesota. 



[Senate, No. 115.] 28 



