Contributions to Palaeontology. 



187 



shown. If this sandstone consist of both that above and 

 that below the Calciferous, or of the St. Peters and the 

 Potsdam proper, then at some point we should expect to 

 find a change of character, or nonconformity between the 

 beds, to indicate the lapse of time in the deposition of the 

 Lower Magnesian limestone of more southern localities ; 

 and this view is sustained by the observed want of con- 

 formity between the sandstone and Magnesian limestone 

 near Dead river just cited. 



Admitting the deposition of the lower sandstone of the 

 Mississippi valley to have been continued in its higher 

 stage into the region of Lake Superior, it seems remarka- 

 ble that the rock now exposed along its shore 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 Wisconsin, 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 only known representative in kind are the 

 two beds of sandstone already noticed, alternating with 

 massive formations of magnesian limestone, and together 

 having a thickness of one hundred and twenty feet. The 

 actual thickness of the sandstone in the northern localities 

 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 twenty feet of sandstone 

 in Missouri; and this is divided into two bands, which may 



