D. Dana on American Geological History. 331 



From this epoch to the close of the Cretaceous, there were no 

 contemporaneous revolutions, as far as we can discover. But 

 the Cretaceous Period terminates in an epoch of catastrophe 

 which was the most universal on record, all foreign Cretaceous 

 species having been exterminated, and all American, with a few 

 doubtful exceptions* This third general revolution was the 

 prelude to the Mammalian Age. But there is no time to do this 

 subject justice, and I pass on, — merely adding, on account of its 

 interest to those who would understand the first chapter of 

 Genesis, that there is no evidence whatever in Geology, that the 

 earth, after its completion, passed through a chaos and a six 

 days' creation at the epoch immediately preceding man, as Buck- 

 land, in the younger days of the science, suggested, on Biblical, 

 not on Geological, ground. No one pretends that there is a fact 

 or hint in Geology to sustain such an idea : on the contrary, it is 

 utterly opposed to it. 



II. The question of the existence of a distinct Cambrian sys- 

 tem is decided adversely by the American records. The Mol- 

 lusca in all their grand divisions appear in the subdivisions of 

 the Lower as well as Upper Silurian, and the whole is equally 

 and alike the Molluscan or Silurian Age. The term Cambrian, 

 therefore, if used for fossiliferous strata, must be made subordin- 

 ate to Silurian. 



The Taconic system of Emmons has been supposed by its au- 

 thor to have a place inferior to the Cambrian of Sedgwick, or 

 else on a level with it. But the investigations of Hall, Mather, 

 and Bogers, and more lately of Logan and Hunt, have shown 

 that the Taconic slates belong with the upper part of the Lower 

 Silurian, being, in fact, the Hudson Biver shales, far from the 

 bottom of the scale. 



III. The American rocks throw much light on the origin of 

 coal. Professor Henry D. Bogers, in an able paper on the 

 American coal-fields, has well shown that the condition of a 

 delta or estuary for the growth of the coal-plants, admitted even 

 now by some eminent geologists, is out of the question, unless 

 the whole continent may be so called ; for a large part of its 

 surface was covered with the vegetation. Deltas exist where 

 there are large rivers ; and such rivers accumulate and flow 

 where there are mountains. How, then, could there have been 

 rivers, or true deltas of much size, in the Coal Period, before 

 the Bocky Mountains or Appalachians were raised ? It takes 

 the Andes to make an Amazon. This remark has a wider ap- 

 plication than simply to the Coal Era. 



IY. In this connection, I add a word on the idea that the rocks 

 of our continent have been supplied with sands and gravel from 



* This catastrophe may not have been violent ; it may have been ages in accom- 

 plishment ; yet it was disastrous to the living tribes over the whole sphere. 



