116 THE DESICCATIOiSr OF LATEE GEOLOGICAL TIMES. 



course these fossils are the remains of land or fresh-water animals and plants ; 

 and so great is their number and so various and extraordinary their char- 

 acter that their investigation, in the hands of Professor Marsh especially, has 

 furnished one of the most interesting and important contributions ever made 

 to the science of palseontology in any country. The study of the lithological 

 characters of the detrital materials can hardly fail to throw light on some of 

 the obscure points in the geological history of the region in question ; but as 

 yet the data are so imperfect that much must be left undecided. 



All the principal divisions of the Tertiary epoch are represented in the 

 lacustrine accumulations of the Cordilleras ; but the older members occupy 

 much more space than the newer. The Eocene is represented chiefly in the 

 region lying between the Rocky Mountains and the Wahsatch Range. The 

 lowest member of this division of the Tertiary has, according to the investi- 

 gations of the Fortieth Parallel Survey, a maximum thickness of about 5,000 

 feet, consisting chiefly of rather coarse sandstones, with intercalated clayey 

 layers, the formation containing coarser materials near the ancient shores. 

 The fossils are mollusks in abundance, with a few fishes, and a wonderful 

 variety of other vertebrates. For this oldest of the Tertiary lakes of this 

 region Mr. King has proposed the name of Ute Lake. This body of water 

 filled the entire Green River basin for a distance of 150 miles nortli of the 

 fortieth parallel, and with an unknown extension to the south, but probably 

 for 200 miles farther in that direction, making its total length 350 miles or 

 more; its breadth must have reached 150 miles. During the period of the 

 existence of this body of water the Uinta Range foi'med an island in it, not 

 far removed at its western end from the main-land, and it Avas from this 

 quarter that the detrital material which was deposited in Ute Lake chiefly 

 came. After the accumulation of the beds (the Vermilion Creek series) 

 which form the base of the Eocene, within the liuiits of the depression in- 

 dicated above, Mr. King considers that a period of orographic disturbance 

 ensued, as the result of which an extensive area of the adjacent laiul on the 

 west was depressed, so that the breadth of the lake was doubled. As thus 

 enlarged it extended west to the 116th meridian. The rocks deposited over 

 this newly formed area of depression consist chiefly of fine-grained shales and 

 marls, containing many remains of fishes and fresh-water mollusks, besides a 

 few beds of lignite. Over these shales is a heavy deposit of ferruginous sand- 

 stone. The enlarged Ute Lake, called by Mr. King Gosiute Lake, diminished 

 in size in consequence of orographic disturbances combined probably with 



