86 



University of California Publications in Geology [Vol.11 



in these beds. At one horizon near the top (the outcrops are along 

 the same creek but stratigraphically below locality 78) a layer of 

 white shale was found full of impressions of Pteropods, thus indicating 

 the marine origin of these upper beds. This portion of the section 

 in the vicinity of Markley Canon has a thickness of between four 

 hundred and five hundred feet. The thickness is somewhat greater 

 in the vicinity of Kirker Creek. 



Probable relation to Kreycnhagen shale. — It will be pointed out 

 later that the San Lorenzo series of the region of Mount Diablo 

 represents the same general period of deposition as that of the Kreyen- 

 hagen shales, recently described by Robert Anderson and R. W. 

 Pack,'' 5 which extend from the Coalinga district to within a few miles 

 of the Mount Diablo Quadrangle. The greater portion of the Kreyen 

 hagen shales to the south represents fairly deep-water conditions of 

 deposition ; the Oligocene deposits around Mount Diablo are, for the 

 most part, of shallow-water origin. The diatomaceous shales of the 

 Markley formation represent the same condition of deposition as 

 existed during most of the Oligocene time further south. 



Fauna. — The following molluscan species were obtained from the 

 diatomaceous, light-colored shales of the Markley formation : Acila 

 muta, Leda pulchrosinuosa, Malletia packardi, Pecten alterlineata and 

 Yoldia species. Of these, Acila muta, Leda pulchrosinuosa and 

 Pecten alterlineata are found in the San Ramon formation of the 

 Concord Quadrangle, while Malletia packardi occurs in the Kirker 

 formation, both in this section and in that of the Sobrante anticline. 



Kirker Formation 



The Markley formation is overlain by about four hundred feet of 

 sandstones, tuffs and tuffaceous sandstones, to which has been given 

 the name Kirker formation. These beds of the Kirker formation, like 

 the larger part of those of the Markley formation, represent shallow - 

 water conditions of sedimentation. 



Disconformity. — Before the Kirker formation was laid down, there 

 was a period of erosion which, if we may judge from the coarse con- 

 glomerates found at the base of the Kirker formation, was probably 

 due to crustal movements in the general region of the Coast Ranges. 



At one locality, 06 a little less than a mile west of Kirker Creek, a 



Anderson, Eobert, and Pack, Bobert W., Geology and oil resources of the 

 west border of the San Joaquin Valley, north of Coalinga, California, U. S. Geol. 

 Surv., Bull. 603, pp. 74-78, 1915. 



60 University of California locality 78. 



