On American Geological History. 409 



material evidence of an epoch of violence and catastrophe : and 

 with this deposit the Upper Silurian began. 



The Upper Silurian has also its three great periods, — the Nia- 

 gara, the Onondaga, and the Lower Helderberg, besides many 

 subordinate epochs, — each characterized by its peculiar organic 

 remains, — each evidence of the nearly or quite universal deviista- 

 tion that preceded it, and of the act of omnipotence that reinstated 

 life on the globe, — each, too, bearing evidence of shallow or only 

 moderately deep waters when they were formed ; and the Onon- 

 daga Period, — the period of the New York salt rocks — telling of 

 a half-emerged continent of considerable extent. 



Another devastation took place, and then opened, as De Ver- 

 neuil has shown, the Devonian Age or Age of Fishes. It commen- 

 ced, like the Upper Silurian, with coarse sandstones, evidence of a 

 time of violence ; these were followed by another grit rock, whose 

 few organic remains show that life had already reappeared. Then 

 another change, — a change evidently in depth of water, — and 

 limestones were forming over the continent, from the Hudson far 

 westward : the whole surface became an exuberant coral reef, far 

 exceeding in extent, if not in brilliancy, any modern coral sea ; for 

 such was a portion, at least, of the Upper Helderberg Period. 



Again there was a general devastation, leaving not a trace of 

 the former life in the wide seas ; and where were coral reefs, es- 

 pecially in the more eastern portion of the continental seas, sand- 

 stones and shales accumulated for thousands of feet in thickness, 

 with rarely a thin layer of limestone. Thus passed the Hamil- 

 ton, Chemung and Catskill Periods, of the Devonian age. The 

 life of these regions, which in some epochs was exceedingly pro- 

 fuse, was three or four times destroyed and renewed — not renew- 

 ed by a re-creation of the same specie 5, but by others ; and al- 

 though mostly like the earlier in genera, yet each having charac- 

 teristic marks of the period to which it belonged. And while these 

 Devonian Periods were passing, the first land plants appeared, 

 foretellers of the age of verdure, next to follow. 



Then come vast beds of conglomerate, a natural opening of a 

 new chapter in the record, and here it is convenient to place the 

 beginning of the Carboniferous Age , or the Age of Acrogens. 

 Sandstones and shales succeeded, reaching a thickness in Pennsyl- 

 vania and New Jersey, according to the Professors Rogers, of 

 thousands of feet ; while in the basin of the Ohio and Mississippi, 



