14 GEOLOGICAL SURVEY OF THE TERRITORIES. 



I will just here state briefly tlie history of the growth of the evidence 

 in regard to the age of the liguitic group as expressed in my previous 

 reports. As far back as 1854 and 1855, the writer was exploring the 

 Tertiary formations along the Missouri liiver, and made large collec- 

 tions of shells and plants, most of which were new to science. These 

 explorations were continued each year up to the autumn of 1860, in 

 various parts of the Northwest, and annually large additions were made 

 to the collections both of vegetable and animal remains. The shells 

 were all of extinct species, of brackish or fresh-water origin, and, while 

 they did not appear to be positively characteristic of any age, were 

 regarded by Mr, Meek as more nearly resembling Tertiary types than 

 any other. The fossil plants were mostly of extinct species ; and in his 

 most valuable chapters contributed to the " Eeport of the Exploration 

 of the Yellowstone and Missouri Eivers," during the years 1859-'60, Dr. 

 Newberry expressly states that they are of Tertiary age, and most prob- 

 ably Miocene. Now, these lignitic strata occupy a' vast area in the 

 Upper Missouri Valley, extending far southward, with very little inter- 

 ruption, to New Mexico, and westward into the interior of the continent. 

 I have many times, in my previous reports, expressed the opinion that 

 the lignitic formations of the West were all portions of one great group, 

 intei-rupted here and there by mountSin-chains, or concealed by more 

 modern deposits. Having, therefore, fixed the age of these beds on the 

 Upper Missouri, and subsequently tracing them across the country, 

 southward below Santa Fe, and westward nearly to Salt Lake Valley, 

 I ventured to express the opinion, from the identity of the fossil flora, 

 that all the lignitic strata of the West might be of Tertiary age. In the 

 summer of 1808, 1 made an examination of the lower coal-beds at Bear 

 River City and at Coalville, Utah, and made the statement that the 

 evidence seemed to point to the Cretaceous age of these beds. Since 

 that time the proof of the Cretaceous age of the lower coal-beds in Utah, 

 especially at Bear River and Coalville, appears to be conclusive. But 

 if we admit that the coal-beds of Wyoming and Colorado are all of Cre- 

 taceous age, I think we may extend them all over the Northwest and 

 ignore the evidence from the fossil flora entirely. The facts, as we pos- 

 sess them at the present time, seem to point to the conclusion that the 

 deposition of the lignitic strata commenced during the latter portion of 

 the Cretaceous period, and continued on into Tertiary times without any 

 marked physical break, so that many of the Cretaceous types, espe- 

 cially of the vertebrata, may have lingered on through the transition- 

 period, even into the Tertiary epoch. I propose to discuss this very 

 important problem in detail at some future time. Each year's explora- 

 tion adds immensely to our knowledge of the vast Cretaceous and Terti- 

 ary groups of the West, and the time cannot be far distant when the 

 facts accumulated will enable us to reconstruct the physical history of 

 those remarkable periods. 



Although the survey began its labors near Ogden in the Great Salt 

 Lake Basin, yet we shall delay only to note a few features which seem 

 important. The geology of this great basin, from the Sierras to the 

 Wahsatch Range, will doubtless be ably discussed in the forthcoming 

 volumes of Mr. Clarence King, in charge of the geological exploration 

 of the fortieth parallel. The results of this survey will prove of the 

 highest importance to Rocky-Mountain geology. The survey under my 

 charge i% annually accumulatitig materials looking toward a more com- 

 plete discussion of the principal geological features of this interior 

 region, should the much-looked-for period of leisure ever arrive to digest 



