134 NEW YORK STATE MUSEUM 



rect the misapprehensions into which the former terra incognita and 

 our blind reliance on unsupported fossil evidence led us ; a means 

 of showing, for instance, the true stratigraphic relations of the Sara- 

 togan fauna as developed in New York to the Upper Cambric faunas 

 in Missouri and Texas, or of the Dictyonema f 1 a b e 1 1 i - 

 forme and the Tetragraptus zones, or the Tribes Hill and other 

 Canadian formations to the Saratogan and later Ozarkic formations 

 on the one side and the typical Ordovicic formations on the other. 

 It is believed that the revised classification proposed by Ulrich ac- 

 complishes this aim. The table given on page 129, though in- 

 tended to show only the relations of the New York formations dis- 

 cussed in this paper, gives a fair general idea of the proposed 

 scheme. 



Perhaps the most practical feature of the revision of the Eopale- 

 ozoic systems, so far as the use of fossils in their separation is con- 

 cerned, is that we can say that the cephalopods and the coiled gas- 

 tropods, also true cystids, became prominent for the first time in the 

 Ozarkic, that the true graptolites, true ostracods, true Orthidae and 

 the Asaphidae are first seen in the Canadian, and that the tabulate 

 and rugose corals, the cyclostomatous and cryptostomatous bryozoa, 

 the pelecypods and the crinoids are well developed in the Ordovicic 

 but unknown beneath this system. In short, the new arrangement 

 is in accord with, and makes available in the broader stratigraphic 

 correlations, the apparently definite vertical distribution of many im- 

 portant organic types. This distribution has not been considered 

 as it should be in the prevailing indefinite arrangement of the 

 Eopaleozoic rocks. As hitherto conceived the cephalopods and gas- 

 tropods, the Asaphidae and Orthidae, and the graptolites appear at 

 undetermined stages in a " Cambrian " system that has no more pre- 

 cise top than the fortuitous first appearance of certain fossil types, 

 arbitrarily assumed to be Postcambric, above a similarly indefinite 

 upper 'limit of certain Cambric genera of trilobites and brachiopods. 



Obviously, there has been no uniformity of practice. Walcott 

 extended the lower system as far up in the section as he could 

 recognize certain Cambric genera. Others, with the laudable but 

 insufficiently considered intention of fixing the boundary at a well 

 defined stratigraphic break, went farther and drew the top of the 

 Cambric at the base of the St Peter, while others with a similar 

 intention extended the base of the Ordovicic down to the first break 

 beneath the introduction of the cephalopods and coiled gastropods, 

 that is to practically the base of the Ozarkic. More commonly, 



