AKNOLD — THE PALEONTOLOGY AND STRATIGRAPHY OF SAN PEDRO. 49 



shells rests horizontally upon the upturned edges of the Cretaceous at several local- 

 ities around Benicia. These are similar to the beds noticed as occurring on the 

 shore between Martinez and Bull's Head Point, which contain fragments of bones of 

 large animals and rolled Tertiary shells. Similar beds, with oysters, were observed 

 on San Pablo Bay between Point Pinole and the Embarcadero; at this locality the 

 beds containing oysters, which rest horizontally on upturned strata of the Tertiary, 

 are elevated twenty feet above the level of the waters of the bay. At Benicia, also, 

 there has been an elevation of several feet since the oyster beds were deposited. 

 With the shells of oysters, those of other species, all now living in the waters of the 

 bay, are found. These deposits evidently belong to the post-Pliocene, and they are 

 of the same age as the beds of gravel, with boulders of gray .sandstone, containing the 

 bones of the mastodon and horse, which occur at Bottle Hill near Benicia." 



The Pleistocene deposits on the shore of San Pablo Bay between the Union 

 Oil Refinery and Point Pinole have been visited by Dr. Merriam and the writer. 

 The deposits, which rest on the upturned edges of the San Pablo strata, consist of 

 horizontally bedded layers of sand, gravel, and clay. Teeth of the mammoth, and 

 bones of the giant sloth and extinct bison have been found in these Pleistocene layers 

 by Dr. Merriam. In certain places the Pleistocene layers consist almost entirely of 

 oyster and mussel shells. 



List of Fossils from the Pleistocene Deposits on San Pablo Bay between the 



Union Oil Refinery and Point Pinole. 



Ostrea lurida Oslrea conchaphila Mylilus edulis Tagelus cali/ornianus 



The character of these Pleistocene strata and of their fauna leads the writer to 

 coiTelate them with the upper San Pedro series. 



Deposits of soft yellow sand resting on the Mei'ced (Pliocene) strata in the 

 vicinity of Lake Merced on the San Francisco peninsula have been assigned to the 

 Pleistocene by Lawson' and Ashley.^ The line of demarkation between the Plio- 

 cene and Pleistocene at some places mentioned by these authors seems to be in doubt. 

 Both are agreed that there is an unconformity between the two series, and Ashley 

 thinks that there was a period of subaerial erosion between them. 



The Pleistocene deposits mentioned by Ashley^ as occurring along the tops of 

 the sea-cliflfs from Montara Point south are partly of fresh-water and partly of marine 

 origin. Those at Purissima are certainly of marine origin, for pholas borings have been 

 found in the old beach-line on which they were deposited. The deposits along the upper 

 edge of this same terrace in the vicinity of Halfraoon Bay are of fresh-water origin, 

 and are very recent. The Haliotis mentioned by Ashley as occurring in these 

 deposits are from Indian kitchen-middens, common at many places along the Califor- 

 nia coast. Similar kitchen-middens near San Mateo have been reported as Quai'ter- 

 uary b}' the same writer. 



' The Geology of the San FranciBco Peninsula. By A. C. Lawson. 15th Ann. Eep. U. S. Geol. Surv., 1895, p. 463. et seq. 

 » The Neocene Stratigraphy of the Santa Cruz Mountains of California. By G. H. Ashley. Proc. Cal. Acad. Sci,, 2nd ser., Vol. V, 

 1895, p. 347, et scq. 



' Op. cit., p. 349. 

 C ' ) September 26, 1902. 



