20 CALIFOHN'IA ACAHI'.MY Ol" SCIKNC'KH. 



i;<iiiN(tii)i:A. 



Sfhmarai'lkMlit fXtrnlrirMM, P StromjtiloerntrotunJ'rtinriiirnnuii.V Slrouyj/lorrnlroliit iiU7-iiuralu$, P 



CltUSTACKA. 

 Cancer brnceri, K 



Rkrumi^.. 



Tolnl number i>( gpeciest 247 



Polecypixlii, Hpooii'H 74 



<ia!ilrop<»la, species 165 



SoapliopotU, Hpeoicg 4 



fU-biiioiclcn, upocieii S 



Crnstacen, species 1 



Speoio8 liviiiK nt San Pedro 158 



Percvutage of fniinn 64 



Sp«cies liviuK only north of San Pedro 43 



Percentage of fntinn 17.4 



S|M>ciiuen8 living only uoiith of Snu Pedro 8 



Percentage of fniiua 3.2 



Speoies extinct 31 



Percentage of fauna 12.5 



Speoies of (|uestionablc habitat 7 



Percentage of fauna 3 



This is also a cold water fauna. Not only is there a large percentage of 

 species which arc found living only north of San Pedro at the present time, but of 

 those species in the fauna which are now living at San Pedro, a great many are 

 northern forms. A few distinctly southern forms are found in tlie fauna, however, 

 which shows that tlie cold climatic conditions prevalent along this part of the coast 

 during the upper Pliocene times were beginning to give place to more temperate con- 

 ditions in the early part of the Pleistocene. The fauna of the lower San Pedro .series 

 is a transitional one between the boreal fauna of the Pliocene and (lie waiin water 

 fauna of the upper San Pedro series. The climatic conditions were therefore chang- 

 ing during lower Pleistocene times; and the climate at the end of the period of de- 

 position of the lower San Pedro deposits was much warmer than that at the end of the 

 period of deposition of the Pliocene. The period of denudation between the Pliocene 

 and Pleistocene epochs was one during which the conditions were also changing. 



The lower San Pedro deposits are thought by the writer to be of Pleistocene 

 origin, for several reasons. First, we have a fauna with a low percentage of extinct 

 species. (The high percentage of the list given above is due to the large number of 

 new species and varieties, many of which are close to living forms and are probably 

 living, but which have not been reported.) The large number of species found in this 

 fanna which have never been found in beds of known Pliocene origin, and the lack 

 of several of the typical Pliocene species from its fauna, ofTer two of the strongest 

 arguments in favor of the Pleistocene age of the lower San Pedro series. The state 

 of preservation of the fo&sils is also an item in favor of their comparatively recent de- 

 position. It is worthy of note that in several cases the original coloration of the shells 

 of lower San Pedro fos-sils is still preserved. The sands, too, of this formation are 

 always much less oxidized than those of the underlying Pliocene. An unconformity 

 between this formation and the Pliocene also suggests a lapse of time between 

 the two. 



