410 On American Geological History, 



in the course of this era, the Subcarboniferous limestone was form- 

 ing from immense Crinoidal plantations in the seas.'" 



Another extermination took place of all the beautiful life of the 

 waters, and a conglomerate or sandstone was spread over the en- 

 crinital bed : and this introduced the true coal period of the Car- 

 boniferous Age ; — for it ended in leaving the continent, which had 

 been in long-continued oscillations, quite emerged. Over the re- 

 gions where encrinites were blooming, stretch out vast wet prai- 

 ries or marshes of the luxuriant coal vegetation. The old system 

 of oscillations of the surface still continues, and many times the 

 continent sinks to rise ao-ain, — in the sinkino:, extino-uishino- all 

 continental life, and exposing the surface to new depositions of 

 sandstone, clays, or limestone, over the accumulated vegetable re- 

 mains ; in the rise, depopulating the s^as by drying them up, and 

 preparing the soil for verdure again ; or at times, convulsive 

 movements of the crust carrying the seas over the land, leaving 

 destruction behind. And thus, by repeated alternations, the coal 

 period passes, some six thousand feet of rock and coal-beds being 

 formed in Pennsylvania, and fourteen thousand feet in Nova 

 Scotia. 



I have passed on in rapid review, in order to draw attention to 

 the series or succession of changes, instead of details.f So brief 

 an outline may lead a mind not familiar with the subject to re- 

 gard the elapsed time as short ; whereas to one who follows out 

 the various alternations and the whole order of events, the idea of 

 time immeasurable becomes almost oppressive. 



* This Subcarboniferous Hmestone is sparingly represented in Pennsyl- 

 vania among the sandstones and shales ; but according to Prof. W. B. Rogers 

 it increases to the southward, and in Virginia acquires a thickness of 1500 

 to 2000 feet. 



I The names given to the subdivisions of the Palseozoic rocks are the 

 same that have been laid down by the New York Geologists, whose assidu- 

 ous and successful labors in a territory of so great geological importance, 

 entitle them to pronounce upon the nomenclature of American Rocks. I 

 have varied from the ordinary use of the terms only in applying them to the 

 periods and epochs when the rocks were formed, so as to recognize thereby 

 the historical bearing of geological facts. The Periods and Epochs thus 

 made out are as follows — excluding minor subdivisions which may make 

 Sub-epoclis, and not attempting to give the parallel subdivisions for the 

 "West. On this subject, the volumes and papers by Prof. Hall especially 

 should be consulted. 



