AMERICAN GEOLOGY DECADE OF 1870-1879. 591 



forces which elevated the western portion of the continent were called 

 into operation toward the close of the Cretaceous epoch, and that the 

 gradual rising- continued without a general bursting of the earth's 

 surface until the accumulation of the Tertiary lignite deposits, or at 

 least the greater part of them. Also, that after the fracture of the 

 surface ccramenced and the great crustal movements began to display 

 themselves, the whole country continued rising, though perhaps with 

 intervening periods of subsidence, up to and even including the present 

 period. 



During the years of the civil war western exploration of all kinds 

 was interrupted, Hayden served in the Federal army as a surgeon 

 from 1862 until 1865, resigning to accept the position of professor of 

 mineralogy and geology in the University of Pennsylvania, a position 

 which he retained until ls~2. 



In the summer of 1866 he undertook a second expedition to the Bad 

 Lands, this time under the auspices of the Academy of Natural Sci- 

 ences of Philadelphia. In company with James Stevenson he left Fort 

 Randall, South Dakota, August 3. The trip was made 



Hayden's Second . . • ' 



Expedition to the with a six-mule team and occupied hlty-two days, dur- 



Bad Lands, 1866. . . . , . . f . ~ , ., 



ing which a circuit of six hundred and fifty miles was 

 accomplished. The large and valuable collection of mammalian fossils 

 was described b}' Leidy in his great work of upward of 450 large 

 octavo pages and 30 plates, published under the auspices of the Academy 

 of Natural Sciences of Philadelphia. The work began with an intro- 

 duction of 12 pages on the geology of the Tertiary formations of Dakota 

 and Nebraska, accompanied by a map. In this work Hayden pointed 

 out the possibility of bridging over the chasm heretofore existing 

 between the Cretaceous and Tertiary periods by means of transition 

 beds belonging to the lignite series. He reiterated some of the state- 

 ments made in previous writings, to the effect that, at the close of the 

 Cretaceous period, the Rocky Mountain area was occupied by the Avaters 

 of an ocean with perhaps a few peaks projecting. Near the close of 

 the period the surface had reached an elevation so great as to form 

 long lines of separation between the waters of the Atlantic on the 

 East and those of the Pacific on the West, and then this great water- 

 shed began to rise above the surrounding country and the period of 

 great fresh-water lakes was inaugurated. The elevation during the 

 Cretaceous period he regarded as slow and gradual, but at about the close 

 of the period or in the early part of tlie Tertiary the limit of tension 

 in the crust was readied and long lines of fracture commenced which 

 form the nucleus of the present mountain ranges, including the lofty 

 continuous ranges with a granitoid nucleus along the eastern portion 

 of the Rocky Mountains, as the Wind River, Big Horn, Laramie, or 

 Black Hills. He showed that the Tertiary beds were in part deposited 

 before the upheaval, as indicated by the inclination of the lignite beds. 



