TERTIARY AGE. 493 



limestones, sometimes oolitic in structure ; green sand, like that of the 

 Cretaceous, and equally valued for fertilizing ; buhrstone, a cellular 

 siliceous rock, valuable for millstones, as in South Carolina. 



Although the Tertiary rocks are generally less firm than those of 

 the Paleozoic, there are in some places hard slates and sandstones, not 

 distinguishable from the most ancient. Such rocks occur in California, 

 in the vicinity of San Francisco ; and it is supposed that some crystal- 

 line rocks of the region are altered Tertiary strata. 



There are also whitish beds of earthy or chalky aspect, which consist 

 of siliceous Infusoria, and others formed from the' shells of Rhizopods. 



1. Lignitic Period or Lower Eocene. — In Mississippi, as shown by Hilgard, 

 the Lignitic group covers a large part of the northern half of the State. It consists in 

 some places at base of small estuary deposits, with marine shells ; above these, of clays 

 and sands, with lignite and fossil leaves. He divides it into the Flatwoods and the La- 

 grange groups. The two groups continue north through Tennessee into Kentucky, as 

 observed by Safford, who named the former the Porter's Creek group, and the latter, the 

 " Orange Sand " group ; the former is mostly clayey in its beds ; the latter sandy. The 

 top of the latter contains two or three beds of lignite, and is called by him the "Bluff 

 Lignite; " whole thickness 300 to 400 feet. [Hilgard's " Orange Sand " is Quaternary.] 



In the ITpper Missouri region, the Lignitic formation has a thickness of 2,000 feet, 

 and lies unconformably beneath the later Tertiary beds. It occurs also in the Big Horn 

 region; in the Chetish or Wolf mountains; about Fort Union. It extends far north 

 into British America, and south to Fort Clarke, and beyond to Texas. In the lower 

 part, on Judith River, there are brackish water deposits, containing shells of Oysters, 

 Corbiculce, etc., mingled with fresh-water shells of the genera Viviparus, Melania, etc. 

 (Figs. 908-913, p. 501). (Meek.) 



In the Rocky Mountain region, the Lignitic group of the Green River basin, near 

 Fort Bridger, and other parts, in Wyoming, Utah, Colorado, etc., consists of sandy beds, 

 some of them true marine, more of them having a commingling of fresh-water shells 

 with the marine, which indicates verj^ shallow brackish waters, and a still larger part 

 strictly fresh-water in origin; and in these occur various beds of mineral coal. They 

 occur always upturned, and generally at a high angle, along the east foot of the Wah- 

 satch, and adjoining others of the mountain ranges. The coal beds are well seen on 

 Bitter Creek in Wyoming; on Weber and Bear rivers in Utah; in the Green River 

 Basin, north of the Uintah Mountains; in Colorado; New Mexico, etc. 



The principal localities where the coal is exposed are — In Utah, at Evanston and 

 Coalville (in the valley of Weber River), etc.; in Wyoming, at Carbon, 140 miles from 

 Cheyenne; at Hallville, 142 miles farther west; at Black Butte Station, on Bitter 

 Creek ; on Bear River, etc. ; in the Uintah Basin, near Brush Creek, 6 miles from Green 

 River; in Colorado, at Golden City, 15 miles west of Denver, on Ralston Creek, Coal 

 Creek, S. Boulder Creek and elsewhere ; in New Mexico, at the Old Placer Mines in the 

 San Lazaro Mountains, etc. The coal is of the bituminous or semibituminous kind. 

 That of Evanston (where the bed is 26 feet thick) afforded Prof. P. Frazier, Jr., 37-38 

 per cent, of volatile substances, 5-6 of water, 7-8 of ash, and 49-50 of fixed carbon. 

 At the Old Placer mines, New Mexico, there is anthracite, according to Dr. J. LeConte, 

 affording 88 to 91 per cent, of fixed carbon; specimens from there, analyzed by Frazier, 

 were semibituminous, affording 68-70 per cent, of fixed carbon, 20 per cent, of volatile 

 substances, and about 3 per cent, of water. The region of the" Old Placer Mines is one 

 of upturned and altered rocks, like the anthracite region of Pennsylvania. 



The fact that the Lignitic beds of Mississippi, the Upper Missouri, and the Rocky 

 Mountain region are cotemporaneous, is shown by the identity of several of the species 

 of fossil plants, as made known by Lesquereux. There are also several fresh-water 

 shells of the Upper Missouri region, identical with those of the Green River Basin and 

 elsewhere. 



