1 1 6 



University of California. 



[Vol. 2 . 



mile Beach is a thin layer of ash, about two hundred feet above 

 the most fossiliferous Quaternary horizon. 



The San Pablo formation lias been called Miocene by Conrad* 

 and Gabbf where it is exposed on the shore of San Pablo Ray, 

 Miocene by GabbJ at Walnut Creek, where it contains the same 

 fauna and shows the same sequence of beds, and Pliocene by 

 Gabb§ at Kirker's Pass, to the north of Mt. Diablo, where the beds 

 are indistinguishable faunally, lithologically, and otherwise from 

 those at Walnut Creek. It appears then that at different localities 

 the same formation has been referred to different periods. 



The Merced series was determined as Pliocene by Remond,|| 

 Gabb,^| and Lawson,** has been considered by Ashleytt as 

 mainly Pliocene, but probably including also some Miocene, while 

 Lindgrenfl has recently suggested that it may be correlated with 

 the Pleistocene of the Sierra Nevadas. 



If the Merced series be Pliocene, the San Pablo must be 

 below the upper Pliocene at least. It has already been shown 

 t<> rest above what has been considered Miocene in Contra Costa 

 County. In other words, it probably represents middle Neocene. 

 Such a determination of the age of this formation, it will be 

 noticed, was, to some extent, foreshadowed by the reference of 

 different localities on the same beds indifferent!}' to the Miocene 

 or the Pliocene, by the earlier writers on the Geology of this 

 regi< m. 



* Pacific R. R. Rep., Vol. VI, pp. 69, 71. 



tGeol. Surv. of Calif. Pakeontology, Vol. II, p. icq. 



\ Ibid., p. 2. 



jSGeol. Surv. of Calif. Geology, Vol. I, p. 31. 

 || Ibid., p. 79- 



IjGeol. Surv. of Calif. Pakeontology, Vol. II, p. no. 

 **Bull. Geol. Deptm. Univ of Calif., Vol. I, p. 14.V 

 ftProc. Calif. Acad., Secjnd Ser., Vol. V, p. 312. 



tijour. Geol . Vol. IV, p. 905. — As far as the relative ages of the horizons 

 are concerned, Mr. kindgren's correlation may be correct. This does not, 

 however, by any means necessitate the reference of the Merced to the 

 Pleistocene, as its marine fauna, which has generally been taken to indicate 

 late Tertiary age, really furnishes more data of value in age determination 

 than could be obtained from the fresh-water formations of the Sierra region. 



