298 J. LeConte— Formation of the Coast Range of California. 



with Mr. W. Jackson, a recent graduate of the university, and 

 now a special student of mineralogy, I set off afoot, and 

 walked very leisurely through the out made by the Central Pa- 

 cific Eailroad from the plains adjoining the Bay of San Fran- 

 cisco through the mountains to the San Joaquin plains, a dis- 

 tance of about thirty miles, taking the angle and direction of 

 the dip at every available point. The following diagram is a 

 generalized section made from these observations, showing the 

 structure of this range. The section is supposed to extend 

 from southwest to northeast, i, e., at right angles to the direc- 

 tion of the chain, L. V. being Livermore Valley and J. P. San 

 Joaquin Plain 



The range where crossed by the railroad is divided into two 

 sub-ranges separated by Livermore Valley. Both of these sub- 

 ranges, it will be seen, are composed wholly of crumpled strata, 

 those of the western sub-range or Contra Costa hills being 

 crumpled in the most extraordinary manner. 



The strata throughout the railroad cut are entirely unchanged 

 and very distinct, and their dip may be taken with the greatest 

 ease and certainty : but unfortunately they consist mostly of 

 thin bedded shales and sandstones destitute of fossils, and so 

 similar in appearance that identification of individual strata 

 would be impossible without the most careful and detailed ex- 

 amination. Only in one place did I find any fossils, and these 

 were easily identified as Miocene Tertiary. On account of the 

 infinite number and the sameness of the strata I found it im- 

 possible to identify, and therefore I have not attempted in the 

 diagram to trace the individual strata through the successive 

 folds. But the general structure of the range is, I am sure, 

 truly represented in the section. 



A glance at the section shows that the southwestern sub- 

 range or that next the bay is far the more complex. We have 

 here at least five anticlinals with corresponding synclinals, all in 

 a distance of about six miles in a straight line. The angles ot 

 dip vary from 40° to 90°, the average being about 65° to 70 . 

 This would make the actual length of the folded strata two and 

 a half to three times the horizontal distance through the moun- 

 tain. Now it is not only impossible to conceive of the origin 

 of such structure except by horizontal mashing, but the amount 



