228 University of California Publications in Geology [Vol. 9 



have yielded as high as fifteen or twenty species. Occurring as 

 they do at this locality they are of more than usual value. A short 

 distance south of Thornton Station, on the Ocean Shore Railroad, 

 a number of hard concretionary strata occur interstratified with 

 softer material. In these strata numerous well-preserved echino- 

 derms, Scutella interlineata Stimpson, occur. They are also numer- 

 ous in the localities a short distance above the base of the section, 

 but so far as the writer's experience goes they have not been found 

 above the locality a few hundred yards south of Thornton Station. 

 Along the sea-cliffs north of Thornton Station fossils are fairly 

 abundant. Some of the strata exposed, just above the base of 

 the cliffs, are almost entirely composed of small gasteropods and 

 pelecypods. These localities have previously been referred to as 

 the "upper gasteropod zone". The most peculiar feature of this 

 faunal horizon is that ninety per cent or more of the species found 

 here are also found living. All of the twenty species collected 

 from this horizon by the writer were recognized as belonging to 

 the Recent fauna. On the evidence obtained from the percent- 

 age of living species Ralph Arnold has referred this upper Mer- 

 ced to the Pleistocene age, while the greater portion of the 

 Merced, stratigraphically underlying it, has been placed in the 

 preceding period. From the faunal relations there seems to be 

 little doubt that Arnold's determination is approximately cor- 

 rect. The close resemblance between the Recent fauna and that 

 of the upper Merced seems to suggest the possibility of there 

 being a break between the upper and the lower Merced which 

 can not be accounted for merely by the depositional record. 



The stratigraphic evidence that appears to suggest an uncon- 

 formity in the Merced in the vicinity of Thornton Station has 

 already been given on a preceding page. In addition to this we 

 might add the faunal evidence in support of the unconformity. 

 A short distance south of Thornton Station Scutella interlineata 

 Stimpson, an extinct form, occurs abundantly. To the north of 

 the station the fauna is almost entirely Recent. The space sepa- 

 rating the two localities is hardly more than one quarter of a 

 mile. The apparent break in the two faunas could be explained 

 by having a space without a fauna, the deposition being con- 

 tinuous and the faunas changing by migration and extinction. 

 The apparent discordance in the strata could be explained either 

 by landslide or a fault as well as by unconformity. The evi- 



