44 PALEONTOLOGY OF NEW-YORK. 



westerly through that State into Kentucky and Tennessee. On the 

 western side, it extends through Indiana to the Falls of the Ohio, and 

 thence through Kentucky and Tennessee, where the declining elevation 

 of the axis permits the two outcrops to unite. The same group, in one 

 or more of its members, has been recognized in Missouri*, and it is 

 probably co-extensive with the subcarboniferous formations of the 

 west. 



This group therefore is very widely spread over the United States, 

 resuming the same area, and being, so far as we know, co-extensive 

 with the Niagara group ; which preceded the physical changes that for 

 a time modified the area of deposition, and restricted to a more east- 

 erly rone the sediments and calcareous accumulations of the interme- 

 diate groups. 



With the limestones of this period, we recognize the beginning of 

 the true Ichthyic fauna, which was first indicated in the Schoharie grit. 

 The fossils of this period, though not yet known to be so abundant or 

 BO remarkable as those of the same period in Europe, nevertheless 

 correspond in character with those of the Old Red sandstone of England 

 and Scotland. 



With the advent of the fishes at this period, we find that there is a 

 remarkable accession of corals, and the variety of form and the num- 

 ber and size of species is much greater than at any preceding period. 

 We may follow the outcrop of this formation, bearing in many places 

 the aspect of a coral reef, along a line of more than fifteen hundred 

 miles from its eastern f to its most southwesterly extremity; and 

 returning northward on the other side of the axis, trace it for nearly 

 a thousand miles from Tennessee to Mackinac ; extending thus from 

 latitude 46 on the north to latitude 33 on the south, and occupying, in 

 its greatest width, twelve or fifteen degrees of longitude. When we 

 reflect that this has probably at one time been an unbroken expanse of 



• Report of Prof. Swallow. 



t In estimating the extent eastward, I do not include the evidences of limestone of this age in the 

 Orean-mountain range in Canada, as shown by Sir William Logan, nor similar evidences in the 

 Connecticut-riTor valley in the north part of Massachusetts. 



