670 



INDEX TO THE STRATIGKAPHY OF NORTH AMERICA. 



The upper portion of the formation is characterized by massive, coarse conglomerate with 

 interbedded sandstone. The conglomerate shows evidences of much crushing, faulted and 

 crushed pebbles being plentiful in it." 



The Chico of the northern portion of the valley of California was described by 

 Diller and Stanton.^**^ A recent account by Diller ^''^^ is contained in the Redding 

 folio. He says in part that the Chico formation is composed chiefly of yellowish 

 sandstone which is in places pebbly and which, though conglomeratic toward the 

 base, passes upward into gray shales. It extends throughout the Sacramento Valley 

 and is covered by later formations except around the valley borders. Northeast- 

 ward it extends through Lassen Strait between the Klamath Mountains and the 

 Sierra and possibly connects with the Chico of northern California and Oregon. The 

 greatest thickness observed in the Redding quadrangle is about 500 feet. The forma- 

 tion thickens rapidly southwestward from Redding and is conformably underlain 

 by the older beds that constitute the Horsetown and the Knoxville. It rests with 

 marked unconformity on the older formations around the north end of the Sacra- 

 mento Valley, and it is unconf ormably overlain by the lone, which has generally been 

 assigned to the Miocene. 



I-K 17-18. ATLANTIC COASTAL PLAIN. 



See contribution by W. B. Clark, Chapter XIV (pp. 608-614). 



J 12. PLATEAU PROVINCE OF UTAH AND COLOBADO. 



In southwestern Utah the Upper Cretaceous comprises Colorado strata and 

 Montana ( ?) strata, and the Colorado is coal bearing. The stratigraphy is stated by 

 Richardson ®*' in the following table and comment : 



Outline of coal-hearing and associated rocks in the southern Utah coal region. 



Throughout the plateau province * * * Upper Cretaceous strata lie directly upon beds^ 

 of Jurassic age. * * * ^i^ ^j^j^ y^g^j of conglomerate at the base may be of Dakota age. The 

 greater part of the Cretaceous rocks, including the coal, are assigned to the Colorado, but the 

 upper few hundred feet contain fresh-water shells and plants of undetermined age, which may 

 possibly belong to the Montana. The succession of Cretaceous strata in the southern Utah 

 region is unlike that in western Colorado and northeastern Utah, so that the formation names 

 used in the coal fields of those areas can not be applied to the rocks in the area under considera- 

 tion. The coal in southern Utah is older than that in the Uinta Basin region, which includes the 



o For list of fossils see the work cited. — B. W. 



