88 University of California Publications in Geology [Vol.11 



horizon in the San Pablo (Upper Miocene). Turner determined the 

 tuff to be rhyolitic in composition. 



The tuff beds, as found about a mile west of Kirker Creek, grade 

 up into a fine, fossiliferous sandstone, which has a thickness of less 

 than fif ty feet ; leaf impressions are quite common in these sandstones 

 and also at a number of horizons in the tuff beds below. To the east 

 of Kirker Creek, these upper beds are lacking and the tuff beds come 

 in contact with the San Pablo ; this is due to the unconformity between 

 the Kirker beds and the San Pablo. As the beds of the Kirker forma- 

 tion are followed to the east, they gradually thin out, and the San 

 Pablo beds rest on lower and lower horizons, until, two and a half 

 miles east of Kirker Creek, on the west side of Markley Canon, only 

 ten or fifteen feet of the tuff is present, while on the east side of the 

 canon the tuffs are absent and the San Pablo rests first upon the sand- 

 stones .iust below the tuffs and then, a little farther to the east, upon 

 the upper beds of the Markley formation. 



In the vicinity of Markley Canon and of Kirker Creek there is a 

 general difference in strike of about twelve degrees and in many places 

 a difference in dip of ten degrees or more between the upper San 

 Lorenzo beds and those of the San Pablo. Pholad borings are very 

 common along the contact, and boulders derived from the San Lorenzo 

 are common in the basal conglomerates of the San Pablo. 



Fauna. — A fairly large fauna has been obtained from the Kirker 

 formation. Some of the species found in the basal beds are : Acila 

 shumardi, Dosinia mathewsonii, Macrocallista pittsburgensis, Solen 

 gravidus, Spisula occidental-is, Spisula ramonensis, TelUna oregon- 

 ensis, Yoldia cf. oregona, Agasoma gravidum, Molopophorus cf. bipli- 

 catus, Solarium lorenzocnsis, etc. 



Some of the species found in the tuffaceous beds above are : Acila 

 muta, Acila gettysburgensis, Cardium lorenzocnsis, Malletia packardi, 

 Modiolus kirkensis, Modiolus pittsburgensis, Tellina lorenzocnsis, 

 Pseudoperissolax merriami, Dentalium conradi, etc. 



