1912] 



Clark: Neocene Section at Kirker Pass 



55 



mult iradiat ns, Ostrea titan, Saxidomus nuttalli, Tresus nuttalli, 

 and Crepidula rugosa. No evidence of faimal zones was found 

 within the Lower Division of the San Pablo. 



Upper Division. — Above the massive cross-bedded sandstones 

 in the Kirker Pass section there are several thin layers of hard, 

 dark-gray sandstones, which weather a rusty brown. These hard 

 layers cap one of the larger hills about one mile to the west of 

 Kirker Creek. These layers are lenticular and along the strike 

 in places grade into concretionary sandstones. This zone is 

 very persistent and served as a basis for separation of the 

 lower division of the series from the upper. Impressions of 

 leaves and pieces of silicified wood are found in abundance, both 

 above and below these hard layers. Turner, in his paper on 

 "The Geology of Mount Diablo," reports the occurrence in this 

 zone, of fossil leaves of the following species, determined by 

 Lesquereux : 



Diospyros virginiana, var. turneri, Laurus, cf. canadensis Heer (?) 



Lx. Viburnum, cf. rugosus Pers. (?) 



Magnolia californiea Lx. Vitis, sp. unci. 



Just below the hard layers of sandstone mentioned above 

 is a very marked irregular contact. This irregularity is seen 

 between coarse sandstones above and fine shaly sandstones below. 

 This contact was first called to the attention of the writer by 

 Mr. Graham Moody. The irregularity was traced for a distance 

 of nearly a mile. In some places there is as much as three to 

 four feet of relief. As far as could be determined, there was 

 no difference in dip and strike between the beds above and 

 below. That the irregtdarity is due to erosion, there can be no 

 doubt. The great abundance of leaves and silicified wood along 

 this zone has already been mentioned. Also along this horizon 

 there is a series of silicified trees that stand perpendicular to 

 the dip of the beds. In some cases indications of roots were 

 observed. One can hardly doubt that these stumps are in place. 



To sum up, it may be said that an unconformity at this 

 horizon in the San Pablo series is shown : ( 1 ) by an irregular 

 contact; (2) by the great abundance of fossil wood and leaves 



« Bull. Geol. Soc. Amer., vol. 2, p. 497, 1891. Description of Leaves, 

 TI. S. National Museum, vol. I, II, p. 35, 1889. 



