TERTIARY PERIOD. 503 



These percentages are expressed graphically in the diagram, Fig. 

 842. In these, as in the strata of all periods, however, there are certain 

 characteristic species by which the epoch may be known, without 

 counting the number of species and calculating the percentage of liv- 

 ing. When mammalian species are found, these are especially charac- 

 teristic of the epoch. Again : Although Tertiary mammalian species 

 are all extinct, the genera and families are not all, so that the first 

 appearance of living families and genera are also very characteristic of 

 the different epochs. 



Rock-System — Area in the United States. — On the Atlantic border, 

 going southward, there is no Tertiary, except a small patch on Martha's 

 Vineyard, on 3 the coast of Massachusetts, until we reach New Jersey. 

 From this point southward the Tertiary is a broad strip, about one 

 hundred miles wide, bordering the coast, and shown on the map (p. 291) 

 by the space shaded with oblique lines running to the right. It con- 

 stitutes the low-countries of the Southern Atlantic States. At its 

 junction with the metamorphic region of the up-countries, there are in 

 nearly all the rivers cascades which determine the head of navigation. 

 Here, therefore, are situated many important towns — e. g., Kichmond, 

 Virginia ; Raleigh, North Carolina ; Columbia, South Carolina ; Au- 

 gusta, Milledgeville, and Macon, Georgia. This has been called the 

 Fall-line. The same strip of flat lands borders also the Gulf, expands, 

 in the region of the Mississippi Eiver, northward to the mouth of the 

 Ohio, and then continues around the western border of the Gulf. In 

 the Gulf-border region, however, the Tertiary is in contact below with 

 the Cretaceous, instead of with Archaean, as on the Atlantic border. 

 This whole Atlantic-border and Gulf-border Tertiary is, of course, a 

 marine deposit. 



In the interior, on the Plains and in the Rocky Mountain region, 

 there are enormous areas of fresh-water deposit, some Eocene, some 

 Miocene, and some Pliocene, which are of extreme interest. 



Among the Eocene basins the most remarkable are : 1. The Green 

 River basin. 2. The Uintah basin. Both of these are on the east side 

 of the Wahsatch Mountains, and separated from each other by the 

 Uintah Mountains, one being north and the other south of that range. 

 They were possibly once united, but now separated by erosion. The 

 strata of the Green River basin are 6,000 to 8,000 feet thick. 



Among the Miocene basins the most interesting are : 1. The White 

 River basin, in Nebraska. 2. The John Day basin, of Oregon. This 

 latter is 5,000 feet thick, but is largely overlaid by the great lava-flood 

 of the Northwest. 3. Patches of Miocene scattered about in Nevada 

 basin region show that deposits of this age cnce extended far south into 

 Nevada and Eastern California (King). 



Of Pliocene basins : 1. Niobrara (or Loup-fork) basin, occupying 



