Features in History of Life on Pacific Coast 

 fornia. Especially in western Washington and 

 southern California there are enormous thicknesses 

 of beds referred to this period. At least three dis- 

 tinct divisions of the Miocene can be made on the 

 basis of the faunas, and this number will doubtless 

 be greatly increased by further study. In the im- 

 mediate vicinity of San Francisco Bay excellent sec- 

 tions of the Miocene can be studied, but the thickest 

 sections are represented in the southern portion of 

 the state. In the vicinity of Coalinga good expos- 

 ures of the Miocene may be seen with the Eocene 

 and Pliocene. 



Important Pliocene occurrences are those in the 

 Merced series near San Francisco, where a splendid 

 section of approximately 5000 feet is exposed. Good 

 faunas are seen again at Purisima south of the 

 Merced region, and in the Etchegoin formation near 

 Coalinga, on the western side of the Great Valley of 

 California. 



In Pleistocene time the sea had retreated to the 

 outermost border of the continent, but deposits of 

 great thickness were laid down at some locali- 

 ties. The fauna is abundantly represented in many 

 sections. The best known Pleistocene of the West 

 Coast is that of San Pedro in southern California. 

 The fauna of this locality has been admirably de- 

 scribed in a memoir by Dr. Ralph Arnold. Accord- 

 ing to this description the lower portion of the San 

 Pedro Pleistocene represents a cold-water stage, 

 while the upper San Pedro was laid down under 

 conditions of somewhat higher temperature. In 

 addition to the abundant invertebrate fauna of the 

 upper San Pedro, there have recently been found 

 in these beds a number of vertebrate remains, which 

 contribute important information bearing on the 

 general problem of time correlation among the 

 Cenozoic deposits of the western region. 



History of the Vertebrates. — The relatively 

 large area covered by a thick mantle of strata depos- 

 ited in a sea in the region west of the Sierra- 

 Cascade Range has given large opportunity for the 

 preservation of marine invertebrates, and the proba- 

 bilities of preservation of vertebrates, excepting 

 fishes and marine forms of the higher groups, are 

 relatively small. 



In the Great Basin Province no marine inverte- 

 brates are found in rocks of later date than the 

 Jurassic period, and following this time fresh-water 

 and land-laid deposits presented large chance of 

 entombment of the higher types of vertebrates. 

 For these reasons the history of the Pacific Province 

 is known largely in terms of the stages of develop- 



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