32 THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 
very crest of the main divide, although widening out and occupying a broad 
area on the eastern slope, towards Pyramid Lake, and in the ranges to the 
northeast of it. In a cross-section of the Sierra from Honey Lake to Oroville 
there is hardly any well-marked granitic rock visible, excepting a small 
patch around Spanish Peak. A little farther north the volcanic sets in, 
forming a complete mantle over the subjacent rocks. After passing this 
broad spur of the great volcanic overflow which covers nearly all of North- 
eastern California, to the east of the Sierra, we have again, in the region 
lying to the northwest of the Upper Sacramento, or Pit River, granitic rocks 
occurring in large quantity and forming the summits of the very broken 
and elevated ranges which, as before stated, occupy most of the surface in 
Trinity, Klamath, and Del Norte counties. 
As granite forms the axis of the Sierra Nevada, it naturally constitutes the 
greater portion of the highest summits of that range. The exceptions to 
this rule are chiefly to be found in those cases where these culminating 
points are exclusively of volcanic origin, as is the case with Silver Mountain 
and Lassen’s Peak, or where the lava forms a thin capping on the granitic 
mass, as for instance on Mount Stanford, and many other points in the vicin- 
ity of Lake Tahoe. The intimate connection between the granitic and 
volcanic rocks is shown in many places, as will more properly be noticed 
farther on. 
The form and picturesque appearance of mountain ranges and their domi- 
nating summits are largely dependent on the structure of the rock, or the 
form of the fragments and masses into which it separates as it weathers. In 
the case of the granitic rocks of the Sierra there is, almost everywhere in 
the range, a well-marked tendency to divide into lamine or plates of vary- 
ing thickness, and these plates have a concentric structure, so that the sur- 
face presents a succession of mammillated forms on a gigantic scale. This is 
well seen in the view from Sentinel Dome, above the Yosemite, looking 
across towards Mount Hoffmann. The whole surface of the county in this 
direction is a succession of domes, looking from a distance perfectly smooth, and 
wonderfully symmetrical. The Half-Dome —so stupendous an object as 
seen from this point — is one of these dome-shaped masses which has been 
split in two, one half having become engulfed at the time of the formation 
of the chasm at its base. Mount Hoffmann is another of these half-dome 
shaped masses, and in both of these, as well as in many others in the Sierra, 
a close examination will show that they are made up of an innumer- 
