170 The Hydraulic Beds, etc., 



signation of Corniferous limestone and Schoharie grit). I 

 have accepted and advocated this view of the age of these 

 formations, which seemed to be sustained by large num- 

 bers of identical fossils from the two distant regions; and 

 I believe that their relative age has not, up to the present 

 time, been formally called in question. 



As might naturally be expected, the subdivisions re- 

 cognized in the east and in the west do not always coincide, 

 but it is usually quite possible to correlate these different 

 members by a comparison of their fossil contents. The 

 main limestone (the great coral reef, comprising the On- 

 ondaga and Corniferous limestones of the [N'ew York 

 system) seems to have been originally unbroken, at least 

 from the valley of the Hudson nearly and perhaps quite to 

 the line of the present valley of the Mississippi. It is 

 traceable in unbroken continuance from the Hudson to 

 the is'iagara rivers, and through Canada West to Lake 

 Huron, and thence into Michigan ; while in a southwesterly 

 direction are the outcrops on the two sides of the Cincin- 

 nati axis, extending through Ohio and Indiana, and thence 

 into Kentucky, where it gradually thins out. During the 

 formation of this remarkably extensive coral reef, there 

 could have been no great change in the conditions of the 

 ocean ; for not only do these corals indicate an undisturbed 

 and luxuriant growth, but the same genera and the same 

 species prevail over a large part of the above area. It is 

 only in the superjacent beds that we may look for changed 

 conditions, which have given origin to the different terms 

 used to designate the subdivisions of the formation in dif- 

 ferent parts of the country. 



In I^ew York we have the following members of the 

 series, between the Marcellus shale and Oriskany sand- 

 stone : 



