

506 



STRATIGRAPHY OF THE BED-ROCK SERIES. 







Though in a certain general sense it may be said, perhaps, that the Sierra consists essentially of 

 an axis of granite flanked by sedimentary rocks, yet there is another and a stricter sense in which 

 this is not true. By far the greatest bodies of granitic rock which occur in the range are found, it 

 is true, in its higher and central portions. But the granite is by no means confined to this portion 

 of the range, nor does it seem to be confined to any two definite belts, one occupying the central 

 portion, and the other the western foot-hills of the range. On the contrary, it occurs in broad, 

 irregular patches, scattered over the western slope of the range, here and there, from base to 

 summit. 



The stratigraphy of the metamorphic rocks of the Sierra is a puzzle to me. On the western 

 slope their strike is almost universally northwest and southeast, and their dip almost as universally 

 at very high angles towards the northeast, that is, towards the crest of the range. These rocks 

 are locally disturbed, of course. Their strike sometimes varies considerably within short distances, 

 and sometimes their dip is to the southwest of the vertical ; but these local disturbances are not 

 so great but that the whole series of auriferous slates may be said to be conformable from the base 

 of the range to the highest points at which they occur toward the summit. Yet the aggregate 

 thickness of these strata is, in many parts of the range, so enormous as to make it hardly credible 

 that they can constitute a single consecutive series, deposited between the earliest epoch to which 

 any of the stratified rocks of the Sierra have been proven to belong, and the upheaval of the range 

 in the Jurassic. 



But if these rocks be not a consecutive series, then how and by what means have they been 

 folded in such perfectly parallel masses, presenting only their broken and eroded edges at the sur- 

 face, and dipping at such universally high angles to the northeast 1 There is, indeed, no lack of 

 possible causes and conceivable forces which might have produced such a result ; but I know of 

 no positive proof that any particular force or set of forces is the one that has produced it, even 

 if such be the Diet at all. In fact, so far as my own knowledge is concerned, the whole question 

 of the stratigraphy of the metamorphic rocks of the Sierra is yet a mystery. One fact which adds 

 yet more difficulty to the problem is the frequent absence of any noticeable amount of local dis- 



turbance in the immediate vicinity of heavy masses of granitic rock. This fact is so frequent that 

 I know not how to account for it on the supposition that the granitic rocks are all eruptive ; and, 

 taken in connection with the occasional distinctly bedded structure of the granite, and the occur- 

 rence in it — in some localities at least — of hornblendic nodules of lenticular form, with a general 

 parallelism in the directions of their axial planes, it seems to me at least very suggestive of the 

 question whether a portion at least of the Sierra granite may not be metamorphic in origin. In 

 this connection I may allude once more to that characteristic Mount Whitney form which is 

 repeated in so many of the culminating peaks of the range on the west of Owen's Valley. There 

 has surely been some special cause for the repetition of this same form so frequently there, nor can I 

 readily believe that it has been exclusively the action of external forces. Whatever may be due 

 to the sculpturing power of ice and snow, or to the character and direction of other erosive forces 

 which have aided in carving the peaks, I cannot help thinking there is probably something in the 

 structure or texture of the rock itself which lias contributed in no small degree to the production 

 of this peculiar form. 



With reference to the greater morphological features in the structure of the Sierra at large, I 

 believe that these, except in so far as they have been subsequently modified by volcanic and 

 erosive action, existed from the beginning, or at least from a very early period in the history of the 

 range ; that is to say, I believe that the greater and loftier spurs which stretch here and there so 

 far down the western slope of the range, and mark the dividing lines between the greater of the 

 modern drainage basins, as, for example, the ridge between the South and Middle Forks of the 

 American, and also the greater of the isolated ridges which, in places far down on the western 

 slope, rise high above everything else around them, as, for example, the Calaveras County Bear 

 Mountain ridge, are probably as old in their elevation as the crest itself, and were uplifted with it 

 to heights above the adjacent regions. 



