14 FOSSIL FISHES OF SOUTHERN CALIFORNIA 



The white shales about Shorb and El Modena are well known to be diato- 

 maceous and often considerable bodies of these rocks, that is, a considerable 

 thickness of them is comparatively free from grit. I have been accustomed to 

 regard these shales as of Puente age, as I believe they have been classified by Dr. 

 Arnold, and I have been of the opinion that the Puente formation is middle or 

 lower Miocene in age, and is the equivalent of the Monterey, taken in that sense. 



The Puente group is certainly not the base of the Miocene in the region 

 about Los Angeles, and in the localities mentioned in your letter, namely, Shorb 

 and El Modena, the beds are near the middle, or a little below the middle of the 

 Miocene section. 



I presume you have some information regarding the large number of fossil 

 fishes found in the diatomaceous beds of near the same horizon some three or 

 four miles south of Lompoc, Santa Barbara County. The rock here is almost 

 entirely made of diatom material some 600 to 800 feet thick. 



I believe that diatoms, or the marine species of the Monterey group, are, 

 or were northern forms, and lived in the cooler waters of the north Pacific of 

 the Miocene, and were brought south by the ocean currents of the time, and were 

 trapped and impounded in such favorable places as were found along the Pacific 

 coast of the period. 



Such favorable places were local, and more or less land-locked, or protected 

 areas of sea, free from sedimentation from the land, and where the surface waters 

 of the sea were free to enter and escape, but where they were detained long 

 enough to lose their contents of northern forms under conditions of temperature 

 too high to permit their survival. It appears to me that the deposits of diatomaceous 

 strata, as they are known in California, are all more or less local, and in their 

 occurrence and distribution, conform to this idea. 



I have also imagined that the climatic conditions of the coast in middle 

 Miocene times were different from those before and after, for there is a well 

 known change in the character of the sediments of the Miocene, those of the 

 middle being largely organic and those of the lower and upper Miocene being 

 generally coarse detrital matter in which the organic contents are inappreciable. 



It may be that physiographic changes in the continental border and in the 

 ocean currents could have brought about these differences in sediments, but there 

 are certain established facts that point to great climatic changes during Miocene 

 times. 



As to the length of time covered by any of the epochs of the past and 

 embraced in the Miocene or Eocene, or in the interval between, I have no very 

 exact idea. 



Strata of supposed Oligocene age have been found in the Santa Monica 

 range, as well as Eocene, but I have no information at hand regarding their 

 occurrences. 



The following localities are represented in our collections: 



(1) Los Angeles. 



1. Los Angeles City. Collection of J. Z. Gilbert, of Ray G. Van Cleve, 

 and of high-school students assisting. These are mostly from clay shales 

 or thin sandstone. Of the species thus obtained, the new Blue-fish, 

 LOPHAR MIOCENUS, in Dr. Gilbert's collection, is the most important. 



