510 CENOZOIC TIME — MAMMALIAN AGE. 



across the country to the Platte River. They are the hurial-place of the Titano- 

 therium and other extinct Tertiary Mammals, and contain also a few fresh-water 

 shells of extinct species. 



The beds are referred to the Miocene by Leidy. 



There are also in the Wind River valley, and on the west side of the 

 Wind River Mountains, other fresh-water deposits, 1500 to 2000 feet thick, 

 called the Wind River group, which may be of the same age as the above, or 

 possibly intermediate between them and the Lignitic group. (Meek & 

 Hayden.) 



The age of some of the Lignite beds is not yet wholly beyond doubt. This 

 is the case, as Hilgard observes, with the Northern of Mississippi, as they have 

 not been seen underlying the marine beds with shells. Yet their position in the 

 State between the Cretaceous in the northeast corner and the acknowledged 

 Claiborne across its centre, favors the idea of their being intermediate in age, 

 and sustains Hilgard's arrangement of them. The Lauderdale beds are un- 

 questionably under the Claiborne. Moreover, beds with similar fossil leaves 

 occur in Arkansas at the base of the Tertiary of that State, as shown by the 

 sections, and also in Texas. 



The Eocene age of the Great Lignite formation of the Upper Missouri, 2000 

 feet thick, is doubted by some. But, as Meek & Hayden observe, (1) it underlies 

 the Titanotherium Tertiary, and is therefore older, and, being of so great thick- 

 ness, it must extend down into the Eocene; (2) the brackish-water beds in its 

 lower part, containing Oysters, Mclanise, etc., show that the deposits were formed 

 when the Cretaceous seas were disappearing, and changing to the fresh-water 

 areas of the later epochs; (3) the remains of a species of Lepidotus, an Eocene 

 genus, occur in the beds. 



There is a Lignite deposit at Brandon, Vermont, associated with a bed of 

 Limonite iron-ore and abounding in fossil fruits, first described by E. Hitch- 

 cock. The plants, according to Lesquereux, are of the same period with those 

 of the Mississippi, Tennessee, and Arkansas Lower Lignite beds. 



The principal source of doubt in all these cases comes from the fact that the 

 fossil plants, as both Lesquereux and Newberry say, are most analogous to 

 those of the European 3/iocene. The geological evidence that they are Eocene 

 appears, however, to be too strong to be thus set aside ; and, if admitted, the 

 difference between Europe and America as to vegetation is quite parallel with 

 what is observed in the Cretaceous ; for the American Cretaceous plants and 

 the beds containing them have been pronounced by European palaaontologists 

 to be Tertiary, notwithstanding the stratigraphical impossibility. 



Yorktown Epoch. — Miocene. — The Yorktown beds cover a large part of the 

 Atlantic Tertiary border, occurring at Gay Head on Martha's Vineyard; in New 

 Jersey, in Cumberland co. and elsewhere, and fossils may be collected in the 

 Marl pits of Shiloh, Jericho, etc. ; in Maryland, at St. Mary's, Easton, etc., 

 occurring on both sides of the Chesapeake for a great distance ; in Virginia, at 

 Yorktown, Suffolk, Smithfield, and through the larger part of the Tertiary 

 region. 



In California and Oregon the beds referred to the Miocene consist of sand- 

 stone and shale, and are in some places 1500 feet thick. They occur near Asto- 

 ria, on the Columbia River and Willamette ; at San Pablo Bay, near San Fran- 



