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122 NEW YORK STATE MUSEUM 



DISTRIBUTION OF THE GUELPH 



In the identification of the Guelph fauna in North America difficulties 

 arise from two sources, firstly from the evident failure to discern 

 between the Niagara and Guelph rock in some regions, again from the lack 

 of reliable fossil lists of the upper Siluric. On account of the changing 

 correlations of the upper Siluric beds in some of the states with advancing 

 knowledge such an inquiry has to assume the character of a history of 

 investigations upon the Guelph in these states. We, therefore, present 

 here such a history which will furnish the data for a summary statement 

 of the distribution of the Guelph in North America. 



After Professor Hall had recorded the existence of " Onondaga salt 

 group" fossils in Wayne county, N. Y. and in Ontario, he discovered dur- 

 ing his geologic investigations of Iowa 1 a limestone at the Rapids of 

 Le Claire, Iowa of which he says : 



"In descending the Mississippi river the Niagara limestone is suc- 

 ceeded by a gray or whitish gray limestone. The whole mass is semi- 

 crystalline, very porous, and vescicular from the solution and removal of 

 fossils." He thought that it might exceed 600 feet in thickness and adds : 



So far as we are able to ascertain this important formation has not 

 heretofore been recognized in western geology, or, if recognized, has been 

 confounded with the Niagara limestone. From this, however, it is quite 

 distinct, both in its lithological character and its fossil remains. 



The fossils are all in the form of casts, and among them is a small 

 Spirifer, a Spirigera, a Pentamerus undistinguishable from P. occiden- 

 talis, several gastropods and some chambered shells. In this reconnais- 

 sance no very complete collections were made, but as far as they enable us 

 to form an opinion, the fossils of the limestones of the Le Claire rapids are 

 very similar to those of the limestone of Gait in Upper Canada. The simi- 

 larity of position is worthy of notice. 



Should the identity of the limestone of these two distinct localities be 

 proved, it will afford sufficient ground for separating these beds from the 

 Onondaga salt group, and for establishing a distinct group. It seems quite 

 probable that the limestones of this period have their eastern extremity in 

 central New York, where, from their small development, as well as from 



1 Geol. Sur. Iowa. 1858. 1:73-80. 



