Geol.— Vol. II.] ANDERSON— STRATIGRAPHIC STUDY l6l 



the head of the Jacalitos Creek, and at the Devil's Den, 

 south of the Sunflower Valley. The Cretaceous rocks in 

 the vicinity of the New Idria quicksilver mines have long 

 been known. From there they extend southeasterly to Coa- 

 linga. In the Knoxville portion the only fossils so far dis- 

 covered are species of A7ninonites, (^Hoplites), Beleniuites, and 

 imperfect plant remains. 



The Chico rocks, which are chiefly in evidence north of 

 Alcalde Creek, and still more so north of Los Gatos Creek, 

 form a thick series of yellow clay shales and tawny colored 

 sandstones. To the north of Los Gatos Creek they extend 

 high up on the range and constitute the most conspicuous 

 formation of the mountain as seen from the south and east. 

 The sandstones predominate, and make up two quite distinct 

 members of the upper part of the Chico, with thick beds of 

 yellow clay shales between. The upper sands of the Chico 

 are characterized by large sandy concretions of a brown 

 color, which have a tendency to split horizontally or to fall 

 apart in concentric shells or laminae. 



Thus far species of Inoceramus are the only fossils found 

 in these concretionary rocks, but Baculites have been found 

 in close connection with them near the coal mine west of 

 Coalinfja. The concretionarv sandstone has a maximum 

 thickness of some four hundred feet where it is exposed nine 

 miles north of Coalinga. The yellow shales below the con- 

 cretionary sandstones contain masses of nodular limestone 

 from which were obtained at different points the following 

 species: 



Baculites chicoensis Gabb Inoceravius zchitneyi Gabb 



Baculites sp. Perissolax brevirosiHs Gabb 



Lytoceras sacya Forbes Architectonica sp. 



Desmoceras (rel. D. hoffmanfii Gahh) Gyrodcs sp. 



Pectunculus veatchi Gabb Cimilia obliqua Gabb, etc., etc. 



The Chico rocks stand at a high angle all along the range, 

 and vary in strike to conform to the underlying Franciscan 

 and other rocks. For the most part all the Cretaceous rocks 

 strike northwesterly or a little north of west. Perhaps the 

 averajje strike of the Cretaceous rocks is N. 60° W. How- 



