1 1 THE BOOK CLIFFS COAL FIELD. 
west in the area examined. Near Green River the formation is vari- 
able. In places south of Elgin the sandstone thins out to a few feet 
and locally disappears, while nearby it thickens to 40 feet or more. 
Some exposures show considerable conglomerate, while others show 
but little conglomerate and much sandstone. 
Characteristic Dakota leaves were found in the sandstone near Elgin 
and in the vicinity of Woodside. They were examined by F. H. 
Knowlton, who furnishes the following lists: 
Dakota fossils from Woodside. 
Laurus protesefolia Lesq. 
Laurus modesta? Lesq. 
Dakota fossils from Elg in . 
cf. Pecopteris striata Heer, from the Unter Ataiiekerdluk (Cenomanian) 
beds of Greenland. 
Gleichenia sp.? 
Torreya oblanceolata Lesq . 
Pinus sp. (cone scales). 
Liquidambar integrifolium Lesq . 
Andromeda linearifolia? Lesq. 
Salix protesefolia Lesq. 
The Dakota sandstone is underlain by several hundred feet of red, 
green, and purple shales with intercalated layers of buff sandstone and 
thin blue limestone. A number of dinosaur a bones have been found 
in these beds, which probably represent the Morrison formation. The 
contact between the Cretaceous (Dakota) and Jurassic is not every- 
where distinct, but in several localities the former is exposed lying un- 
conformably on an undulating surface of varicolored Jurassic shale. 
MANCOS SHALE. 
The Mancos shale forms the base of the Book Cliffs (Mount Garfield,. 
PI. IV), where it is sculptured into badland topography, and it 
underlies the broad valley between the cliffs and the hills of Dakota 
sandstone to the south. It is a fissile black, blue-gray, and drab clay 
shale, which contains local lenses of limestone, and, at the top, thin 
beds of buff sandstone. The shale constitutes a distinct lithologic 
unit in which there is little variation, though the color of the lower 
part is generally darker than the upper. It is much broken by cracks 
and joints, which frequently contain thin saline films. These locally 
effloresce in patches of white powder, some of which were found to 
consist chiefly of calcium carbonate, and the unreclaimed areas of 
shale are characteristically coated with " alkali." Lenses of blue-gray 
fossiliferous limestone, from several inches to a few feet in thickness, 
oRiggs, E. S., The dinosaur beds ol Grand River valley, Colorado: Field Columbian Mus. geol. series, 
vol. 1, 1901. 
