394 Transition Rocks of North America. 



limestone, the Genesee slate, the Portage group, and the 

 Chemung group, and for the west all the strata between the 

 top of the cliff limestone and the bottom of the carboniferous 

 limestone. 



The Ponent series includes all the rocks between the base 

 of the Catskill red sandstone and the top of the overlying con- 

 glomerate. (Formation X. of the Pennsylvania and Virginia 

 Annual Reports.) It usually embraces but two formations, 

 the Ponent red sandstone, and the Ponent conglomerate, 

 though the former of these requires for some districts a triple 

 subdivision. 



The Vespertine series comprehends the interesting formations 

 above the horizon of the Ponent conglomerate, and below that 

 at the base of the great conglomerate under the coal measures. 

 In Pennsylvania, it is composed of the thick red shale deposit 

 of the coal regions ; and in Virginia, of a much more complex 

 set of strata, including a lower red shale or variegated marl, 

 next a great thickness of carboniferous limestone, and then an 

 upper set of shales with alternating sandstones. In the west- 

 ern states, on the other hand, it consists almost exclusively of 

 the carboniferous limestone and its subordinate chert. 



The Serai series embraces one vast and multiform body of 

 coal strata, the thickness of which in Western Pennsylvania 

 and Virginia, exceeds three thousand feet, being in the an- 

 thracite basins probably still greater. The lowest or oldest 

 subdivision of this series, is the Serai conglomerate, and the 

 true coal formation overlying this, is divided into four distinct 

 members, — the older coal measures, older shales, new coal 

 measures, and new shales; these last terminating the entire 

 succession of one thick and wide-spread Appalachian strata. 



The whole body of rocks here grouped into nine series, con- 

 tains, upon the most careful analysis which we have been able 

 thus far to institute, about forty-eight formations, few, if any, 

 of which are co-extensive with the present limits of the great 

 Palaeozoic basin in which they lie, or even with that part of it 

 included between the Blue Ridge chain, the Mississipi River, 

 and the great Lakes. Those which were the most widely de- 

 posited, are the Matinal magnesian limestone, the Levant 

 older (oi- Niagara) limestone, the Vespertine (or carboniferous) 



