334 CALIFORNIA ACADEMY OF SCIENCES. 



To sum up, it will be seen that out of thirty-one species 

 that were specifically identified, six are not known to the 

 fauna of this region (from San Francisco to Santa Cruz), 

 leaving twenty -five species known in the present fauna, 

 or 8i% of the fossil fauna are living in that region. This 

 by the old method would make the beds Pliocene. But 

 considering the smallness of the fauna and the question- 

 ableness of several of the specific identifications, that 

 method can have but little value here. Nor have any 

 satisfactory results been obtained from a comparison with 

 known Pliocene faunas, for the species are all peculiar to 

 the west coast, or are not known in the fossil state else- 

 where. 



The arguments from the structural side are, that while, 

 as shown by the fauna, this formation is possibly later 

 than Pliocene, it is found to be overlaid by horizontal or 

 nearly horizontal strata containing Elephas bones, with 

 evidence of a land period between. Since these beds 

 were laid down, therefore, there has been a movement 

 which has tilted them at angles of from 5^ to 40°, fol- 

 lowed by their being exposed to subaerial erosion, and 

 later by being submerged and covered by deposits at one 

 place over 200 feet thick and then the whole subjected 

 to a more or less general elevation to its present position. 

 It will thus be seen that our assignment of these strata to 

 the Pliocene is only in a homotaxial sense. ^ 



Not only does the fauna suggest that these upper beds 

 might be considered by themselves, but the structural re- 

 lation to the lower beds is just obscure enough to prevent 

 a positive assertion that they are conformable. The first 

 writers on the subject made them unconformable. 



The presence of Pliocene on the Seven-Mile Beach 

 was noted by Gabb and Remond* at the time of the first 



*Geol. Siir. of Cal., Geology, vol. i, p. 79. 



