174 THE DEVONIAN AND CARBONIFEROUS. | bull. 80. 



or sandstone in the nearest State already surveyed with which to cor- 

 relate it. This custom is satisfactory in some cases, and in others it 

 fails because of the inconstancy of the conditions of sedimentation ; 

 and, using the criterion of fossils, whenever considerable distance in- 

 tervenes, there is clear indication of difference in the time of beginning 

 and ending of a formation which in its general characters may indicate 

 equivalency of age. Doubtless the same principles of correlation have 

 been applied in the interpretation of the formations below and also of 

 those above the Upper Paleozoic. Of these others may speak. This 

 custom having prevailed during the last fifty years, it is in the discus- 

 sion regarding the correlation of the dominant stratigraphic units that 

 we find best expressed the methods and usages employed. 



During the last half century a large number of papers have been 

 written, having as a common theme some form of the problem regard- 

 ing the demarkation between the Devonian and Carboniferous systems. 

 These papers and discussions have gathered mainly about the inter- 

 pretation, taxonomic value and position of the Waverly group, the 

 Kinderhook group, the Marshall group, the Black shale and Goniatite 

 limestone formations, the Catskill, the "Old Red sandstone," and the 

 variously named Conglomerates. 



The determination of the demarkation between the Devonian and 

 Carboniferous systems presented itself under different names to each 

 of the State surveys of the States in which the transition is seen. In 

 New York and the States of the Appalachian Basin it appeared in the 

 discussion regarding the Catskill formation and the Conglomerates; 

 in Ohio it was regarding the Waverly formations ; in Michigan it was 

 the Marshall group ; in Indiana it was about the Goniatite limestone and 

 the Black shale ; in Kentucky and Tennessee it was the Black shale and 

 the Siliceous group; in Illinois it was the Kinderhook group j in Iowa 

 and Missouri it appeared first under the name "Chemung group," later 

 as Kinderhook group in Iowa and as Chouteau group in Missouri. In 

 each of these various States the difficulties were similar: the absence 

 of any satisfactory definite standards of delimitation, either in strati- 

 graphic or paleontologic terms, between the Devonian and Carbonifer- 

 ous systems. 



In New York State the highest pure marine fauna in the Chemung 

 is equivalent in a general way to the upper Devonian fauna of North 

 Devonshire. But some of the species recorded in the upper Devonian 

 of Europe are more conspicuous in formations stratigraphically above 

 the Chemung horizon in America. Again, the Catskill formations in 

 New York, containing estuarian faunas, carry also plants, which on 

 the one hand indicate close affinities with the Carboniferous, but are 

 stratigraphically well below true Carboniferous deposits of the Appa- 

 palachian province. 



When, however, New York series are taken as the standard, the ter- 

 minal part of the Devonian presents no parallel, either stratigraphically 



