674 INDEX TO THE STRATIGEAPHY OF NOETH AMERICA. 



divided into five formations — Dakota, Mancos, Mesaverde, Lewis, and Laramie — 

 and he gives ^^^^ the relations of this classification to those of Hayden, King, Powell, 

 and White, as well as the reasons for abandoning the earlier ones. 



For the Rangely field Gale gives in substance the following account ^'^^ of the 

 several Cretaceous formations: 



The Dakota sandstone presents the following descending section at the southern foot of 

 Blue Mountain, a southern outlier of the Uinta Range: 



Section of Dakota sandstone at Willow Creek. 



Feet. 



1. Sandstone, ■weathered brown (overlain by dark-gray and black slaty shale, supposed to 



represent the base of the Mancos [Benton]) , 10 



2. Shale \ri th beds of white clay and a hard siliceous conglomerate; shale very black and slaty 



near its base ; 110 



3. Sandstone, white, cross-bedded, containing conglomerate layers '. . 40 



4. Interval, probably shale, covered by sandstone slide rock 180 



5. Sandstone 3 



6. Shale, variegated in colors of pink and green, containing also one or more beds of dense 



reddish-purple limestone 95 



7. Conglomerate of coarse, perfectly rounded pebbles in a scant sandy matrix; pebbles largely 



of chert and siliceous material ._ 45 



• 483 



According to Stanton Nos. 4 to 7 may be older than Dakota and may correspond 

 to the Fuson or the Lakota (both Lower Cretaceous?) or to the Morrison formation 

 (Jurassic?). Farther west, in Utah, the Dakota shows much the same divisions as 

 those given above, but the basal conglomerate thins out eastward and the formation 

 is reduced to two thin sandstone beds separated by shale. 



The Mancos shale, which overlies the Dakota, is homogeneous, with the excep- 

 tion of a few sandy layers, and is probably nearly 5,000 feet thick. It includes 

 Benton, Niobrara, and part of the Pierre, and is characterized by Benton fossils 

 near the base and by a Montana fauna "having some Fox Hills elements near the top. 



The Mesaverde succeeds the Mancos and is the youngest Cretaceous remaining 

 in the Rangely field. It consists of massive sandstones, interbedded with sandy 

 shales and many beds of carbonaceous shale and coal. The thickness is about 5,000 

 feet. Gale describes its members in detail. 



North of the Rangely field, in southern Wyoming, Cretaceous strata form the 

 Rock Springs dome in the great area of Eocene. Schultz ''^^ describes the strata 

 there exposed as Mesaverde, Lewis, and Laramie (?) and says: 



The present investigation led to the conclusion that the subdivisions previously mapped 

 by King and Powell could not be applied to the sequence of rock in this region. The fossils 

 collected by this party and studied by F. H. KJnowlton and T. W. Stanton indicate that the 

 several formations have the geologic time values indicated in the accompanying table, where 

 the general character and succession of the Cretaceous and Tertiary rocks, together with their 

 economic importance, are set forth. [Only the Cretaceous part of the table referred to is quoted 

 here.] 



