WinclieJl.J 



4U 



[May ti, 



in New York and Pennsylvania, the Chemung 

 group is succeeded by a coarse sandstone or con- 

 glomerate, which lies at the base of the Red sand- 

 stone. This change is equally great with that 

 which took place at the production of the Oneida 

 conglomerate, and the mass forms a distinct topo- 

 graphical feature in the southern part of New 

 York, and in parts of Pennsylvania. At the same 

 time, all the peculiar organic forms of the Che- 

 mung group have become extinct. ^ ^^ ^. When 

 we undertake to mark the limits between systems, 

 at points where it is difficult to decide them either 

 from lithological or organic characters, (as in the 

 separation of Devonian and Silurian, ) it seems to 

 us very proper to give more importance to such a 

 remarkable line of separation as that indicated at 

 the base of the red sandstone. ^^ ^ ^ The 

 relations between the red sandstone and the Car- 

 boniferous sj'stem appear to be scarcely known at 

 all ; or whether there may, or not, be a more 

 intimate relation between this mass and the suc- 

 ceeding gray sandstones, has never been shown. ' ' 



M. deVerneuil, '"'^ while admitting it incontestible 

 that the Catskill group *' is upon the same horizon 

 as the Old Red Sandstone of Scotland and Wales, " 

 concludes, with emphasis, that the study of the 

 New York strata has resulted in ' ' proving that 

 the Old Red Sandstone, in America, is more recent 

 than the schists and limestones which represent 

 the deposits of the Eifel, the Hartz and of Devon- 

 shire." 



In accordance with the views set forth in the 

 foregoing paper, I append the following table of 

 geological equivalents. The Table, as originally 

 presented to the Amei-ican Association, was pub- 

 lished in the "Geology of Tennessee," pp. 364-5. 

 As here given, it is slightly modified, in the Ten- 

 nessee column, to adapt it to late discoveries al- 

 ready announced. In the Michigan column, I 

 have merged the ' ' Black shale' ' with the ' ' Huron 

 group," in accordance with views long entertained 

 (see especially, Proc. Am. Phil. Soc, No. 81). 

 That this shale occupies a position beneath the 

 Hamilton will not, I think, be longer maintained. 

 Whether it be wholly Genesee, or wholly Portage, 

 or the representative of both, it is certainly a 

 lower constituent of a group of argillaceous strata, 

 which is one mass, physically, and which, in 1861, 

 I was induced to designate as the " Huron Group," 

 in consequence of its extensive outcropping around 

 the shores of Lake Huron, between Detroit and 

 Pt. aux Barques. 



'* See Aiiifr. .Jour. Sri., [2] v.. pp. .'W7. 3ti9. 



