MESOZOIC TIME — CRETACEOUS. 825 



4. Laramie Epoch. — 



2. Upper Laramie or Denver group : fresh-water beds of sand- 

 stone, conglomerates ; and partly of eruptive material (andesytic, 

 etc.) ; with or without coal-beds. 



1. Loioer Laramie: fresh-water beds of coarse, friable sandstones, 

 often cross-bedded, with clay-beds ; occasional fossiliferous brackish- 

 water beds ; with beds of bituminous coal, in some places " 15 to 20 

 coal-beds in 1000 feet ; " thickness 1000-5000 feet. 



3. MoNTA^TA Epoch. — 



2. Fox Hills group: sandstones and shales with many marine 

 fossils ; maximum thickness, 1000 feet. 



1. Fort Pierre group : plastic clays, sand-beds often with limestone 

 concretions ; marine fossils ; maximum thickness 7700 feet. 



2. Colorado Epoch. — 



2. Niobrara group: calcareous marls, chalk, shales, sandstones, 

 with limestones ; marine fossils ; maximum thickness 2000 feet. 



1. Fort Benton group (near Fort Benton) : laminated clays, lime- 

 stone, with marine fossils ; maximum thickness, 1000 feet. 



Probably includes the Coalville coal-bed, with 1500 feet of the 

 lower part of the Coalville group. 



1. Dakota Epoch. — 



Dakota group: sandstones, clays, some lignitic layers, with con- 

 glomerates sometimes at base; fossil leaves abundant, and other 

 evidences of fresh-water origin, and little of brackish or marine 

 waters. Probably includes the Bear Kiver coal-beds. 



The grouping of the subdivisions adopted above (which accords with the 

 results of Meek's paleontological work) and the terms used are those of 

 G. H. Eldridge. The name, Lignitic, used by Meek and Hayden for the 

 Upper division (which they made Lower Tertiary), was changed by King 

 in 1878 to Laramie. Subdivisions of the Laramie into Lower and Upper is 

 based chiefly on the work of Cross (1888 and later). 



The Cretaceous was the coal period of western America. As Paleozoic 

 time, the era of extended continental submergence, closed with the slow 

 emergence of the eastern half of the continent, so Mesozoic time, the era of 

 extensive submergence of the western half of the continent, closed with the 

 slow emergence of this western half. And the later coal-beds, like the earlier, 

 mark long periods of small emergence and persistent marshes in the alter- 

 nating conditions of level. The Upper Cretaceous affords coal at different 

 levels : at Bear Eiver, western Wyoming, and at Mill Creek, British America, 

 in the Dakota group ; at Coalville, Utah, in the Colorado group (Stanton) ; 

 and at Dunvegan, Peace River region (117^° W., 56° N.) (Dawson) ; in the 

 Belly River region, north of Montana, on Vancouver Island, at Nanaimo and 



