94 PALEONTOLOGY OF NEW- YORK. 



conglomerates described by Sir W. E. Logan in the Geological Survey of 

 Canada. 



At the west and southwest the upper beds are often calcareous, with 

 more rarely arenaceous and calcareous strata in the higher part of the 

 group. The transition to the succeeding formation is always strongly 

 marked ; and it is only in rare instances that we have seen beds of 

 passage, with a few of lower species of fossils. 



In the very heterogeneous assemblage of materials and fauna which 

 constitute the Medina sandstone and Clinton group of the New- York series, 

 we have an indication of the recurrence of the causes which produced 

 the Hudson-river group, operating apparently in conjunction with other 

 forces, which have finally culminated in the Niagara group. The evidence 

 of sudden alternation and violent change exhibited in the Clinton group 

 in New- York, long made it a very difficult and unsatisfactory study. The 

 mingled character of its materials, and the very evident relation of its 

 fauna with both lower and higher strata, left the results quite uncertain, 

 with a strong indication that there was something more to be learned 

 concerning its relations with the preceding and succeeding formations. 



With this idea I have followed the line of its outcrop in Canada West, 

 upon the islands of Lake Huron, along the shores of Green Bay, and 

 through Wisconsin. Examinations in all these localities have afforded no 

 additional information beyond what we possessed in New- York. While 

 the Medina sandstone can be identified only in a few points, the Clinton 

 group is more persistent; and with its soft shales and associated iron ores, 

 its beds of sandstone and impure limestone, it is clearly recognized in the 

 State of Wisconsin. The conditions of alternating sea and shallow water 

 and shore seem to have prevailed over the entire extent ; for in Wisconsin, 

 the surfaces of some of the beds are marked by tracks and trails as in 

 New- York*. The fauna of the more westerly localities has afiforded a few 



• I h»TC elsewhere shown the reasons for inferring that the beds with Pentamerus oblongus and 

 P. Uevii, in Great Britain, should be separated from the Caradoc sandstone; and I believe this view 

 is generally admitted. As originally described, the Caradoc beds included species or their analogues 

 which are, with us, unknown below the Clinton group; while the true Caradoc fauna corresponds to 

 thftt of our Iludson-river group. 



