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the strata below the upper limit of the Black River limestone, 

 only three have been observed by Prof. Hall to pass up into the 

 overlying Trenton limestone, and on the same horizon a transition 

 almost as abrupt shows itself in parts of Pennsylvania and Vir- 

 ginia. Here then we would seem to be justified in drawing a 

 strong line of separation between the contiguous Black River and 

 Trenton fauna\ But turning to Canada, we find a very different 

 distribution of the fossils. In this region the Black River lime- 

 stone, that is, the rock containing the characteristic Black River 

 fossils, includes a preponderating number of species found also 

 in the Trenton. According to the Canada paleontologists, fifty- 

 two out of seventy-five are common to both formations, and 

 what is still more interesting, some Trenton species are found in 

 the yet lower group of the Chazy. Here obviously we can no 

 longer draw a limit between the Black River and Trenton faunae, 

 but must blend them gradationally into one. 



A yet more striking instance of the essentially local nature of 

 these lines of demarcation is seen in the corresponding group of 

 formations in Tennessee, where, according to Prof. Safford, the 

 upper Lebanon rocks are more strongly marked with a Black 

 River fauna than the lower, thus in a measure inverting the suc- 

 cession of the fossil groups as compared with New York, and put- 

 ting the Trenton fauna below a group which in New York would 

 be called Black River. 



So again in the passage from the Hudson River group to the 

 overlying rocks, marked in New York and over much of the 

 Appalachian area by evidences of great mechanical disturbance, 

 we find the line of demarcation so strongly drawn that only a 

 few species are continued into the next superior formations. This, 

 therefore, has been well recognized as one of the most abrupt of 

 all the transitions in our paleozoic geology ; and yet toward the 

 northeast, in Anticosti, where these evidences of physical move- 

 ment are comparatively slight, we see the conglomerates and 

 sandstones of the intermediate Levant or Oneida and Medina 

 group replaced by limestones, forming beds of passage which con- 

 tain some of the characteristic fossils of both the lower or Hudson 

 River formation and the superior or Clinton group. Here, there- 

 fore, the lines of separation become so vague or so nearly oblite- 

 rated as to make the proposed limitation of faunis quite impossible. 



