434 GEOLOGY. 



mung. In some places the Catskill beds may represent less than the 

 full Upper Devonian, and in others more. The Catskill formation 

 is sufficiently different from the rest of the Upper Devonian to indi- 

 cate that the sediments of which it is composed accumulated under 

 conditions very different from those which obtained farther west. 

 This formation is poor in fossils, and such as occur are partly, if not 

 wholly, of fresh- and brackish- water forms. Hence it is inferred that 

 the Catskill region was at least so far shut off from the ocean as not 

 to afford the conditions necessary for marine life. The formation is 

 notable for its redness, a feature which marks many other formations 

 made in inclosed or partially inclosed seas, inland lakes, or basins. 



The Catskill formation has a thickness of 3000 feet in New York 

 and twice that amount farther southwest in Pennsylvania. Local 

 beds of sandstone (the Oneonta of central New York), seemingly like 

 the Catskill in origin, occur outside the Catskill region, suggesting 

 that similar conditions now and then existed farther west. 



The thickness of the Upper Devonian in central and western New 

 York approaches 4000 feet, and it is still thicker in Pennsylvania and 

 Maryland, 1 locally reaching a thickness of 8000 or 9000 feet. In Ohio 

 the same series (Black or Ohio shale 2 ) has a maximum thickness of 

 2600 feet, but thins notably to the north and west, being at most only 

 a few hundred, and often but a few score feet thick in Indiana, 3 Illinois, 

 Iowa, southern Michigan, Kentucky, and Tennessee. 4 Various names 

 are applied to the series and its subdivisions in various localities. 



West of the Great Plains, the equivalents of the Chemung of the 

 east have not been separated from other parts of the Devonian system. 

 The Upper Devonian seems also to be represented in Maine and still 

 farther northeast. 5 



The sections of the Devonian given in the Appendix, Vol. Ill, give 

 some idea of the development of the system in various parts of the 

 continent. 6 



1 Prosser, Jour, of Geol., Vol. IX, pp. 415-42. This article is a concise summary 

 of the Paleozoic systems of Maryland. 



2 Geol. Surv. of Ohio, 1873-93. 



3 Twenty-second Ann. Rept. Dept. of Geol. and Nat. Res. of Indiana, p. 17. 



4 Hayes and Ulrich, Columbia (Tenn.) and Campbell, London (Ky.) folios, U. S. ( 

 Geol. Surv. 



6 Williams and Gregory, Bull. 165, U. S. Geol. Surv., p. 22. 



8 The Devonian of special regions east of the Great Plains is described in the text 

 and shown on the maps of the following folios of the U. S. Geol. Surv.: Ala- 



