illiamb.] WINCHELL ON THE MARSHALL GROUP. 181 



Marshall group of Michigan on paleontologjc grounds, the equivalents 

 of the Catskill rocks of New York. 



In the paleoutological part of the paper is given a catalogue of the 

 known fossils of the Marshall group and its supposed equivalents in 

 the United States, with references to the place of publication of the 

 descriptions of the species. Four hundred and sixteen species are 

 enumerated. No attempt is made to determine or eliminate synonyms. 

 The distribution of the species by States is indicated. As the author 

 takes up his argument he first speaks of the fauna of the Huron group, 

 and concludes from a comparison of the species that it is equivalent to 

 " the Portage and Chemung groups, or to some portion of them," and 

 then proceeds to determine whether the overlying Marshall group 

 should be included with the Hurou shales as equivalent to the upper 

 part of the Portage-Chemung of New York. His first argument for 

 equivalency was that furnished by the lists of species identified in two 

 or more States. By this means he correlated — 



(1) The Marshall group of Michigan with (2) the Gritstone and Waverly down 

 to the Chocolate shales of Ohio; (3) the Goniatite limestone of southern Indiana 

 and its equivalent sandstone in northern Indiana ; (4) the Kinderhook group of 

 Illinois ; (5) the yellow sandstone series of Iowa, at least down to the bluish shales; 

 (6) the series known in Missouri as the Chouteau limestones, the Vermicular sand- 

 stone and shales, and the lithographic limestones, and (7) the Silico-bitumiuoua 

 shales at the base of the Siliceous group of Tennessee. 



These correlations had been practically demonstrated for all except 

 the Marshall group by previous writers. 



A long discussion of species then follows, to show that the species 

 contained in these formations have " a Carboniferous aspect," a fact 

 which M. de Verneuil had long before pointed out upon his first glance 

 at the species then known of the Ohio, Indiana, Illinois, Iowa, and 

 Missouri localities. 



The next section announces that " the fauna of the Chemung group 

 presents a Devonian aspect." This fact had been recognized for thirty 

 years, and the Chemung of New York had been the recognized typical 

 upper Devonian for ail correlations in North America. 



Section VI proposes the question "Can the Marshall and Chemung 

 be synchronized 1 ?" Elaborate citations of principles of paleontologic 

 science are made and prolonged argument to prove that this is not 

 reasonable, and to reach the conclusion that the Chemung must remain 

 " within the limits of the Devonian system, where it has been placed 

 by the nearly unanimous judgment of paleontologists," and that "the 

 Marshall group must be admitted within the boundaries of the Car- 

 boniferous system according to the present nearly unanimous judgment 

 of western geologists." 



The one point which is the gist of the whole argument is made in the 

 last section, headed "Parallelism of the Catskill and Marshall." The 

 author's theory is that the Catskill group of eastern New York instead 

 of thinning out or disappearing by lack of sediments in western New 



