Devonian System in North America. 53 



area), and northwestward in Ohio, Canada West and Michigan. 

 On the western side of the Cincinnati axis the section is inter- 

 mediate, but presents closer relations with those of the interior- 

 than with the typical New York section. 



In New York there is a full series of temporary stages of 

 deposition each having its characteristic lithological compo- 

 sition and each holding its distinctive fauna. The lower Hel- 

 derberg limestones were followed, in this area, by a deposit of 

 coarse sand which is thicker and more prominent in the eastern 

 and southeastern part of the region, there attaining several 

 hundred feet in thickness, but thins out toward the northwest, 

 and fails altogether, both in the extreme southwestern and in 

 the extreme northwestern extension of the area. This is the 

 Oriskany sandstone, marked by a few large and well-defined 

 Brachiopods. The Oriskany stage is generally more or less 

 calcareous, and runs up into calcareous shales and grits along 

 the northeastern border of the area. These latter are the 

 Cauda-galli and Schoharie grits of the New York section. 

 They are followed above by the Onondaga and Corniferous 

 limestones, averaging less than a hundred feet in thickness, but 

 reaching three hundred feet thickness, or more, in some parts 

 of New York and in Michigan. 



In this eastern continental area there was evidently some 

 relationship between the sandy deposits beginning in the Oris- 

 kany and the calcareous deposits typically represented in the 

 Onondaga and Corniferous limestones ; for we find in the 

 northwestern part of the area the sandstones thinning out to 

 almost nothing, while the limestones reach their greatest thick- 

 ness, and in the eastern and more southern parts of the area 

 the sandstones reach their greatest thickness, while the lime- 

 stone dwindles and in some parts has not been distinguished at 

 all. The limestone is rich in corals, and in some layers, has 

 abundant Brachiopods ; the latter are types of wide geographi- 

 cal distribution, and, in the more common forms, such as 

 JStrophomena rhomhoidalis and Atrypa reticularis, are species 

 of long geological range. Some of the corals, too, have a long 

 range in the western continental section, appearing in the 

 upper part of the Nevada limestone, according to Mr. Walcott. 



In New York the next lithological stage of the Devonian is 

 a series of shales, often beginning and terminating in black and 

 sometimes partly calcareous shales ; but in the central part of the 

 section, gray, soft argillaceous shales, temporarily calcareous in 

 places, and holding a rich and abundant fauna, constitute the 

 Hamilton stage. The Hamilton also shows tendency to be more 

 calcareous westward and more arenaceous in the eastern out- 

 crops, and the sandstones and arenaceous shales are thicker and 

 predominate in the Pennsylvania, Maryland and Virginia sec- 



