THICKNESS OF CKETACEOUS STKATA. 401 



the Miocene. It also shows a very great thickness of upper Cretaceous 

 strata, all having substantially the same dip. Taking the horizontal dis- 

 tance of the lowermost Tejon beds east of Tasajero creek to the lowermost 

 Tejon south of Lone Tree valley as six and a half miles and the average dip 

 40° from a horizontal, there must be here a thickness of four miles of beds, 

 largely sandstones. 



The upper Cretaceous strata north of the mountain (figure 2) have a hori- 

 zontal thickness of about one and three-fourths miles and a thickness normal 

 to dip of about one and one-eighth miles ; and it is likely that this is not 

 far from their maximum thickness. Consequently a single anticlinal fold 

 will not account for the four miles of strata. It is more likely that two 

 such folds exist here. In this case it would usually be expected to find 

 some of the Tejon and Miocene beds infolded with the Chico, which is not 

 the case. It is possible that these upper beds (Tejon and Miocene) were 

 thrown into shallow folds only, over the double-folded Chico strata, and 

 have since been entirely eroded. 



The main peak of the mountain, especially its southern and southwestern 

 slopes, is composed largely of red silicified shale. This rock occurs abun- 

 dantly also at the head of Bagley cailou, and at numerous other points in 

 the metamorphic area. It is a flinty rock, seemingly well adapted for pres- 

 ervation as pebbles ; yet, although conglomerates exist in all the formations 

 after the Neocomian that are to be found in the vicinity of the mountain, 

 pebbles of this rock are very scarce till we come to the post-Pliocene, where 

 they occur abundantly. Fragments of the red phthanite are to be found 

 also scattered over the country, especially in creek beds for miles around; 

 and, as it is many miles to any other metamorphic area, it is fair to assume 

 that these post-Pliocene pebbles, as well as the angular fragments, came from 

 the metamorphic mass of Mount Diablo. 



The finding of very few pebbles of this rock in any formations preceding 

 the post-Pliocene may be regarded as evidence that the metamorphic mass 

 was little exposed to erosion before the close of the Pliocene. 



The post-Pliocene strata north of Kirker pass, and probably everywhere 

 in the north and northeast, appear to overlie conformably the Pliocene; but 

 the underlying Pliocene, and the Miocene as well, dip at a comparatively 

 small angle (40°) toward the north, and were evidently not so violently 

 affected by the upheaval, being farther away from the center of disturbance, 

 as were the strata south of the main peak. Sections of the strata north of 

 the mountain apparently show continuous deposition from the Neocomian to 

 the post-Pliocene, inclusive ; but that this was not the case has been clearly 

 shown by Mr. Becker* from geological evidence, and by Dr. White f from 

 paleontological evidence. 



* Bulletin U. S. Geol. Surv., no. 15, 1885. 

 t Bulletin U. S. Geol. Surv., no. 19, 1885. 



