180 



Contributions to Palceontology. 



formations in "Wisconsin lie to the west of what appears 

 to have been a great promontory at the time of their deposi- 

 tion, stretching southward from the region of Lake Superior 

 far into the ancient sea. The disconnexion caused by this 

 promontory between the East and the West, would of itself 

 prepare us to expect a fauna, differing, in a great degree, 

 from beds of corresponding age on the opposite sides. 



It has been shown, by the investigations of the Canadian 

 Survey, that not only the Potsdam sandstone, but all the 

 fossiliferous beds below the Birdseye and Black-river lime- 

 stone are absent from Kingston on Lake Ontario to Lacloche 

 on Lake Huron. From Lacloche to Lake Superior, there 

 is a sandstone coming in below the Birdseye limestone, 

 which from its position may be considered as of the age of 

 the Chazy formation, 1 and equivalent to the St. Peters 

 sandstone of Wisconsin and Minnesota; and it is this 

 sandstone, doubtless, which has been taken for the Potsdam 

 sandstone in some localities along that line. 



The succeeding Birdseye and Black-river formation, 

 from Lacloche to Lake Superior, has become a buff-colored 

 magnesian limestone, or weathering externally to this 

 color, but still holding the characteristic fossils. 



In New York, a sandstone (the Potsdam) lies immediately 

 beneath a magnesian limestone ("the Calciferous sand- 

 rock"): this deposit is succeeded by a calcareous forma- 

 tion (the Chazy), including a sandstone, and surmounted 

 by the Birdseye, Black-river and Trenton limestones. 



In Wisconsin, Iowa and Minnesota, we have undoubted 

 Trenton limestone, and below it a buff-colored magnesian 

 limestone containing so many of the characteristic fossils 

 of the Birdseye and Black-river limestones as to leave no 



ir The "Chazy formation " of the Canadian Geological Survey, in its 

 eastern localities, includes a sandstone which comes in below the greater 

 part of the limestone, leaving from ten to twenty feet of shale and lime- 

 stone beneath ( Geology of Canada, 1863, p. 123). It is apparently this 

 sandstone of the Chazy formation, having in Canada a thickness of fifty 

 feet, which has become augmented in its western extension, while the 

 calcareous part of the formation has partially or entirely disappeared. 



