CENOZOIC TIME — TERTIARY. 893 



Miocene and Pliocene beds have been identified in Alaska, and descriptions and a map 

 showing their distribution, by W. H. Dall, are contained in his Bulletin 84 of the TJ. S. 

 a. S., 1892. 



2. Lacustrine Deposits of the Continental Interior and Pacific Slope. 



I. Eocene. — The lacustrine Eocene areas are confined mostly to the summit region 

 of the Rocky Mountains and its broad slopes, and are noted for the abundance of fossil 

 vertebrates. The oldest, according to present knowledge, that of the Puerco basin, covers 

 a large area in northwestern New Mexico, and extends northward into Colorado. The 

 beds rest on the upturned Laramie, and are overlaid conformably by the Wasatch beds. 



The Wasatch basin (W on the map. Fig. 1468), also Lower Eocene, lies to the north of 

 the Uinta Mountains, and east of the Wasatch range. Its original breadth was probably 

 nearly 300 miles, and the extreme length from north to south perhaps 500 miles. The 

 thickness of the beds near the Wasatch range is about 4000'. The Wasatch also occupies 

 a basin extending from New Mexico northward, to the Uinta Mountains and the Big Horn 

 basin in Wyoming. The beds also of the Cuchara basin of R. C. Hills are referred to the 

 Wasatch Eocene. 



Two other basins, the Green Biver and Wind Biver, are situated to the north of the 

 Uinta Mountains, and are intermediate in age between the Wasatch and Bridger. The 

 Green River basin is situated mostly within Wyoming, and has an area of more than 5000 

 square miles. The beds consist of impure limestone below, and thin fissile calcareous shales 

 above, in all 3000' to 4000', and are especially noted for their fossil Fishes and Insects. 

 Fine views of the bluffs and of the " Bad Lands " of the Wasatch are given in King's 40th 

 Parallel Report, on plates 13, 14, 15; and general views of the Green River basin, in 

 Hayden's Report for 1872. The Manti beds of Cope (1880), occurring in Sevier and San 

 Pete counties, Utah, are similar in character and fossils to those of the Green River basin. 



The Bridger basin of the Middle Eocene is situated between the meridians of 1091° 

 W. and 110J° W., and for the most part north of the parallel of 41°. Washakie 

 basin of King (1878), which lies 60 miles farther east, and the Huerfano group of R. C. 

 Hills (1888-1891), are of the same age. The latter lies to the east of the Front Range in 

 Huerfano and Las Animas counties, southern Colorado. 



The Uinta lake basin (U, Fig. 1468), of the Upper Eocene, lies wholly to the south of 

 the Uinta Mountains, and has now a level of about 10,000' above the sea. Its width from 

 east to west is over 140 miles. 



The Amyzon beds, referred to the later part of the Eocene, occur in northeastern 

 Nevada, in South Park, Col., and in central Oregon. They are probably intermediate 

 between the Uinta and White River beds. 



The small Florissant basin is situated 8000' up in the mountains of southern Colorado. 

 Its beds are largely made of volcanic earth, or tufa, and have become famous for their 

 great numbers of fossil Insects and Spiders, and also for their Fishes, and for feathers 

 and other remains of Birds, besides plant remains. 



II. Miocene. — In the Miocene period the Eocene lakes of the Rocky Mountain region 

 had mostly been drained through an increase in the elevation of the land or changes in its 

 surface level ; but the mountain area still remained so low that even greater lakes then 

 existed over what are now the eastern slopes of the mountains. They were situated in 

 the region of the upper Mi.ssouri, and covered most of the state of Nebraska and a portion 

 of Wyoming and Colorado, and extended from Nebraska southward. The area is over 

 350 miles in its maximum breadth, and has a height at the present time, through subse- 

 quent elevation, of about 6000' to the west and 3000' to the east. 



The Earlier Miocene is that of the White River group. Its oldest deposits, the 

 Titanotherium beds of Hayden, consist mainly of variegated clays, together with sand- 

 stones and conglomerates, and have a thickness of 180' (J. B. Hatcher) ; above are the 



