312 J. D. Dana on American Geological History. 



roll ; Hitchcock, the Professors Rogers, the well-known Geol- 

 ogists of the New Yokk Survey, also, Owen, Percival, 

 Morton, Conrad, Tuomey, and many others, have made large 

 contributions to the accumulating results. Yet the system may 

 be said to have been mainly laid open by four sets of observers, 

 • — Morton for the Cretaceous ; Conrad for the Tertiary ; the 

 New York Geologists for the Palaeozoic strata; and the 

 Professors Rogers for the Carboniferous beds and the Appa- 

 lachians. 



The succession of Silurian and Devonian rocks in the State of 

 New York is the most complete in the country, and it was well 

 for the science that its rocks were so early studied, and with such 

 exactness of detail. The final display of the Palaeontology by 

 Mr. James Hall has given great precision to the facts, and the 

 system has thereby become a standard of comparison for the 

 whole country, and even for the world. 



This accomplished, the Carboniferous rocks were still to be 

 registered, and the grand problem of New England Geology 

 solved. The Professors Rogers, in the surveys of Pennsylvania 

 and Yirginia, followed out the succession of strata from the 

 Devonian through the Coal Period, and thus, in a general way, 

 completed the series. And more than this, they unravelled with, 

 consummate skill the contortions among the Appalachians, bring- 

 ing order out of confusion, and elucidating a principle of moun- 

 i tain-making which is almost universal in its application. They 

 showed that the Silurian, Devonian, and Carboniferous strata, 

 which were originally laid out in horizontal layers, were after- 

 wards pressed on to the north-westward, and folded up till the 

 folds were of mountain height, and that thus the Appalachians 

 had their origin ; and that also, by the escaping heat of those 

 times of revolution, extensive strata were altered, or even crys- 

 tallized.* ' 



* As I have already remarked, many names are above omitted which have con- 

 tributed largely to our knowledge of American Geology. 



While Dr. Morton was the first to distinguish the North American Cretaceous 

 beds, and pursued his researches with great energy and skill, they have been largely 

 studied also by Lyell in different localities on the east and south, by Nicollet and 

 recently Shumard, Hatden, Meek and Hall, on the beds west of the Mississippi, 

 by Romer in Texas, Tuomey in South Carolina, H. D. Rogers and others in New 

 Jersey, J. W. Bailey with reference to microscopic species, and J. Leidy for Verte- 

 brate Remains. 



The Tertiary has been investigated by Lyell along both the eastern and southern 

 border ; also in different localities by Morton, M. Tuomey, F. S. Holmes, C. S. Hale, 

 I. Lea, H. D. and W. B. Rogers, Romer, J. D. Dana and W. P. Blake for the ter- 

 tiary of the Pacific coast, Bailey for minute species, Harlan, Owen, Muller, 

 Prout, Leidy, Wyman and Gibbes, for Vertebrate fossils ; while these and many 

 other authors have published on the post-tertiary deposits and organic remains. 



The Silurian and Devonian systems have occupied the attention of nearly all 

 who have written on American Geology, in the East or West, among whom, there 

 are :— Hall, Mather, Vanuxem, Emmons, Conrad, De Verneuil of Paris, the Pro- 

 fessors Rogers, Messrs. Whitney and Foster, D. D. Owen, C. T. Jackson, D. Houghton 



