20 



bly than any other in these particular sections. We are warranted in this con 

 clusion to a considerable extent, by an examination of the equivalents of the 

 southern rocks, found nearly three hundred and fifty miles north, as in the case 

 of the tertiaries situated among the Buttes in the county of Sutter. Here the 

 recent volcanic series is found intruded through the sandstones of these moun 

 tains which bear the same fossils as those noted in the preceding section, while 

 at the distance of twenty miles to the north-east the fossiliferous rocks of later 

 date are found entirely undisturbed by any of those particular intrusions. 



The scoriaceous lavas of this date are well represented by a dike of similar 

 character passing through the upper portion of El Dorado county, and which 

 is found very often in detached masses on the hills betweeu Georgetown and the 



Middle Fork of the American River. Specimen No . In the vicinity of 



the Tejon Pass and on the desert to the south it forms isolated hills known as 

 " Lost Hills," but in passing into the mountains this characteristic becomes im 

 mediately lost ; we here find that they enter and cut through nearly all of the 

 primitive rocks, as well as the sedimentary, and where large dikes are formed, 

 changes of structure are easily observable, the original structure being entirely 

 destroyed. 



It was not uncommon to find jasperoid rocks in the vicinity of these dikes, 

 where they had intruded through either sandstone or slates. In these cases 

 every trace of former organic existence was dissipated, and were recovered on 

 ly by traveling often considerable distances. 



Among other disturbing agents and diifering in general appearance from the 

 lavas, are to be found frequent intrusions of a recent trapean rock (green stone) 

 which is common in many parts of these mountains, but more abundant in the 

 transverse chain to the south ; these rocks are found to penetrate the latter to their 

 southern base, and approach nearly to the coast line in some places ; they can 

 not be considered of cotemporaneous origin with the former by any means, as 

 we find them disturbing a distinct and more recent group of sedimentary, as well 

 as the older rocks. There is every reason to believe that they were intruded as late 

 as the miocene period, as they are in contact with rocks as late as those found on 

 the Carmello. and near Monterey, a part of which Mr. W. P. Blake considers 

 as quarternary, and they certainly are not earlier than the Post Pliocene. 



It is probable that these rocks have been principally instrumental in disturb 

 ing nearly all the late tertiaries, as we find the greatest amount of dislocation 

 among these rocks, when found in contact with this intrusive suite. 



GEOLOGY OF THE SAN BERNARDINO MOUNTAINS. 



The trend of this mountain chain has been stated as being nearly due east and 

 west ; this will be found to hold good for the greater part of its entire length ; 

 and it now becomes necessary to trace as distinctly as possible the peculiarities 

 of the geological structure of its mountains, in order to draw legitimate deduc 

 tions respecting the character of adjacent arable districts lying at their base. 

 The inception of this chain on the west was stated to occur a few miles north 

 of Point Conception, and to follow the above trend nearly or perhaps quite to 

 the Colorado River. 



The geographical position of this chain must exert a powerful influence in 

 modifying the productive capabilities of the adjoining lands as well as also the 

 production of diversified species in the neighboring seas, which we find to be the 

 case, the latter having been fully demonstrated within the past year. 

 ^ These mountains are made up for the most part of the primitive rocks, and con 

 sist chiefly of the granitic series ; they form by far the most of all the higher 

 ridges and more elevated peaks belonging to the chain. 



