156 CALIFORNIA ACADEMY OF SCIENCES [Proc. 3D Ser. 



Preface. 



The systematic study of the field covered by this paper, 

 and its stratigraphy, was begun for purely economic and 

 private purposes and not for publication; nevertheless, so 

 much data and material of a scientific interest have been 

 gathered, and so much information has been acquired, part 

 of which, though of a practical nature, it is permissible to 

 make public, that some of the more general facts are here 

 offered as a contribution to the geological literature of Cali- 

 fornia. 



The matter and conclusions set forth are the result of a 

 field-study extending over a period of more than two years, 

 made partly alone, and partly with the cooperation and aid 

 of Mr. Josiah Owen, whose knowledge of the field is both 

 extensive and practical to a high degree, and to whom are 

 due many of the stratigraphic observations here presented. 



The advantages for a statigraphic and faunal study offered 

 by this field are in most respects unsurpassed anywhere. 

 The aridity of the climate, and the soft and crumbling 

 nature of the younger sediments, together with the action of 

 the wind, combine to give excellent and accessible exposures 

 of rock, while in many cases the almost perfect preservation 

 of the shells and other fossils renders the task of identifica- 

 tion satisfactory. The structure of the rocks, moreover, is 

 generally simple, and strata are readily followed to almost 

 any extent, particularly along the eastern flanks of the range, 

 to which most of the field-work was naturally confined. 



In this connection it is proper to mention the generous 

 interest taken in this work by Professor E. T. Dumble and 

 the many facilities afforded through his kind cooperation. 



The fossils collected during the field explorations, aggre- 

 gating several thousand in number, were donated to, and 

 have become the property of the California Academy of 

 Sciences. 



