374 University of California Publications in Geology [Vol. 7 



series of igneous rocks consisting mainly of andesite and basalt. 

 The Siestan rests upon the lavas covering the Orindan, and is 

 in turn covered by a volcanic series made up largely of basalt. 



The section, from the base of the Orindan to the top of the 

 lavas above the Siestan, contains no marine fossils. It shows 

 scattered through it a few remains of fresh-water Mollusca and 

 Crustacea, land Mollusca, land plants, and land or fresh-water 

 vertebrates. The accumulation as a whole is evidently the result 

 of deposition in a basin which was at times occupied, at least 

 in part, by fresh water, and at other times may have received 

 purely alluvial deposits. 



As our knowledge of the land fauna of the California region 

 west of the Sierras and north of Tehachapi is very meagre, the 

 writer has made special effort during the past ten years to secure 

 material which might furnish some information as to this phase 

 of the palaeontologic record. The great thickness of strata in 

 the Orindan and Siestan seems to offer some of the most favorable 

 places to search for vertebrate forms. The beds being so situated 

 that the relation of the vertebrate fauna to the earlier marine 

 Tertiary faunas is determinable, any information acquired is 

 especially valuable for use in connection with work on the corre- 

 lation of the great marine marginal province and the epicon- 

 tinental Great Basin province of western North America. 



Being easily accessible for investigation, the Orindan and 

 Siestan formations have probably been examined for vertebrate 

 remains more carefully than any other non-marine formations in 

 the California area of the Pacific Coast marginal province. In 

 spite of the efforts put forth, only a very scant fauna has been 

 obtained in the course of the eighteen years since the first sys- 

 tematic search was conducted in these beds. Although the results 

 of our investigation of this fauna are very unsatisfactory, it 

 seems desirable to put the available information on record, as 

 the known relation of these formations to the marine Tertiary 

 of middle California gives unusual significance to all data ob- 

 tained. It is hoped that presentation of the evidence offered 

 here may serve as a stimulus and a guide to future students 

 of the Orindan and Siestan, so that a much more satisfactory 

 representation of the fauna may be secured. 



