TERTIARY AGE. 491 



the inner limit of the region being about one hundred miles from the 

 Gulf in Alabama, and one hundred and fifty to two hundred in Texas'. 

 Along the Mississippi River, the Gulf-border region extends north- 

 ward to southern Illinois. 



Marine Tertiary beds occur also on the Pacific coast, in California 

 and Oregon, forming, with the Cretaceous, the Coast Range of hills. 

 Some of the Tertiary ridges are 2,000 to 3,000 feet in height. They 

 also cover the Cretaceous, over the Rocky Mountain slopes and sum- 

 mit, but alternate, in these parts, with extensive fresh-water beds. 



The beds of the Lignitic period or Lower Eocene are well displayed 

 either side of the Mississippi, in Mississippi, Tennessee, and Arkansas ; 

 over the eastern slopes of the Rocky Mountains, on the Upper Missouri 

 and elsewhere ; over the Rocky Mountain region, in Wyoming, Utah, 

 Colorado, etc., where the thickness is several thousand feet ; in Cali- 

 fornia, overlying the Cretaceous, and in other parts of the Pacific- 

 border region. Lignite, or carbonized wood, and beds of mineral coal 

 occur in the formation. Part of the beds outcrop near the Pacific Rail- 

 road ; and the coal obtained, often called lignite, is used for the 

 engines on the road, and for metallurgical and other purposes. The 

 coal of the vicinity of Mount Diablo in California, and other beds of 

 the Tejon series, appear to be of cotemporaneous formation. 



The Middle and Upper Eocene marine beds, or those of the Ala- 

 bama period, are extensively displayed in the States of Mississippi, 

 Alabama, and Georgia ; they occur also at some points in South 

 Carolina and Virginia, though generally concealed on the Atlantic 

 border by the Miocene beds. They have been divided into the Clai- 

 borne group, or Middle Eocene, well displayed at Claiborne, Ala- 

 bama, and the Vicksburg group, or Upper Eocene, so named from 

 Vicksburg on the Mississippi. Lyell, whose observations in America 

 as well as Europe first brought out the true character and relations of 

 the Tertiary formations, makes the Claiborne beds to be probably the 

 equivalent of the Middle Eocene of Great Britain, stating that several 

 of the shells (among them, Venericardia planicosta Lam.) are identi- 

 cal with those of European species of that age. 



The marine Miocene beds cover a large part of the Atlantic Border, 

 and are well exhibited and full of fossils in Virginia and New Jersey. 



Over the Rocky Mountain region and part of the Eastern slopes, 

 the beds of the Alabama period, as well as the later Tertiary, are of 

 fresh-water origin; and they lie upon the upturned Lignitic beds, 

 generally in a horizontal position, or nearly so. As first shown by 

 Hayden, the beds were formed in lakes that existed over the Rocky 

 Mountain region, soon after it first emerged, and while it was yet a vast 

 extent of low and nearly level land. 



These fresh-water or lake deposits are, as stated, of all periods from 



