594 EEPOET OF NATIONAL MUSEUM, 1904. 



its junction with Green River proper. From Green River Station the 

 route followed the old stage route up Bitter Creek by way of Bridger 

 Pass and the Medicine Bow Mountains, across the Laramie Plains, and 

 through the Laramie Range by way of Cheyenne Pass, back to the 

 point of departure. 



Studies were made also along the line of the Pacific Railroad between 

 Cheyenne and the Salt Lake Valley. No topographer accompanied 

 the party, and the maps used were those constructed by the engineer- 

 ing department of the Army, which were, however, so inaccurate that 

 to delineate the geology upon them in any but the most general way 

 was practically impossible. 



During this season Ha}^den worked out the sequence of the Carbon- 

 iferous and Cretaceous rocks, and made the subdivisions of the latter 

 into Dakota, Fort Pierre, and Fox Hill groups, which are still recog- 

 nized. He remarked that some of the fossils found in southern 

 Nebraska seemed to possess Permian affinities, though as they all 

 extended down into the Coal Measures they could not be considered as 

 characteristic, and therefore those rocks which he had previously 

 mapped and colored as Permian should be relegated to the Permo- 

 Carboniferous. 



He noted the occurrence of Potsdam sandstone with Oholella mi mi 

 and Lingvla at South Pass on the south side of the Sweetwater. The 

 massive granites as well as the intercalated stratified gneisses extend- 

 ing from South Pass City nearly to Pacific Springs were all regarded 

 as of sedimentary origin. He showed that, near the close of the Cre- 

 taceous period, the ocean extended all over the area west of the Mis- 

 sissippi from the Arctic circle to the Isthmus of Darien. A little later 

 the great watershed of the continent w T as marked out and the marine 

 waters were separated into more or less shallow seas, lakes, and marshes, 

 within which greAV the abundant forests that went to form the coal 

 beds. 



From a study of the character of the vegetable impressions found in 

 these beds, he argued that coal strata of contemporaneous origin may 

 be purely marine, purely fresh water, or brackish, dependent upon 

 local conditions. He pointed out that the sea had not had access to 

 the Salt Lake Valley since middle Tertiary times, the sediments from 

 800 to 1,200 feet in thickness, called by him the Salt Lake group, being 

 regarded as of Pliocene age and contemporaneous with the Niobrara, 

 Arkansas, and Santa Fe groups, and of fresh water origin. 



This report of Hayden was accompanied by special reports by Meek 

 on the invertebrate paleontology, by Cope and Leidy on the vertebrate 

 paleontology, by Lesquereux on paleobotany, and by Newberry on the 

 ancient lakes of western North America. The volume marks the 

 beginning of Cope's work with the Hayden survey, which resulted 

 later in the production of the two monographs on the vertebrata of the 



