GRANITIC ROCKS OP THE TETON-DRIFT DEPOSITS-—OAK TREES. 
203 
by several inches of the laminated rock, as is represented in the figure, but no disturbance in 
the structural planes could be detected. These are probably segregations, and not intruded. 
SEGREGATED FELDSPATIC VEIN. 
Beyond this, a short distance, the structural planes are not so well developed, and the rock is 
syenitic, and of a compact and uniform texture, and resists decomposition well. Its trend is 
N. 40° W. In one of the ravines, where a nearly vertical wall of rock is exposed, I observed a 
smooth and undulating surface, similar to that frequently exhibited at the junction of dykes of 
trap with granite, and on the walls of mineral viens, appearing to be the result of motion and 
pressure when the rocks were in a plastic state, and very different from “ slickensides” or the 
grooving and polishing produced on the walls of veins by the sliding of the rocks after their 
consolidation. It is possible that, in this instance, the granite formed the wall of a feldspathic 
vein, now entirely removed by disintegration. 
At station 58, the outcropping granite is gray and compact; and the lenticular masses of 
hornblende and mica, similar to those already described as occurring in Tejon ravine, are well 
developed. Their direction, or trend, is N. 72° W. ; dip north estimated at 50°. The direc¬ 
tion was observed at several places, with the same result as above. This compact granite 
continues to the summit-level with but little variation. The greater part of its surface in the 
valley of the Pass is buried beneath a great heap of erratic blocks and drift-gravel confusedly 
stratified. At the summit, station 140, there are several outcrops of the granite of limited 
extent; it becomes more structural, and contains a large amount of hornblende and mica. The 
mica is olive-green, and is in small plates and obscure crystals. 
The soil which results from the disintegration of the granite and the associate rocks appears to be 
peculiarly favorable to the growth of oaks, of which there are numerous species. 1 Quercus Hindsii, 
or macradenia, is found growing on the rocky ridges and on the drift formation throughout the Pass, 
and is most abundant towards the summit, but attains its greatest size in the valley, in situa¬ 
tions sheltered from the prevailing winds. Pines also grow luxuriantly in the canons of some 
of the highest ridges. From the summit to the Great Basin the rocks are covered by a deep 
granitic soil, and the surface is generally rounded, and in some places supports groves of oaks. 
This, however, is the character along the wagon trail; the Survey followed the course of a 
ravine, or creek, along which the rocks were favorably exposed. Even at the summit it was 
difficult to find good exposures of the rock, there was so much soil and grass. At station 149, 
a short distance below the summit, there is an outcrop of laminated, but compact, hornblendic 
granite, cleaving into rhombic masses ; this is succeeded by granular granite, with a distinct 
structural character. Below this, near station 151, are beds composed almost entirely of horn¬ 
blende crystals, coarsely aggregated, the color varying from black to dark and light-green. In 
1 The following are some of the species of which leaves were obtained and drawings made. They were determined by Dr. 
Torrey : Quercus macradenia; Q. agrifolia; Q. agrifolia, (a dwarf species) ; Q Douglasii; Q. crassipocilla, (n. s.) Torrey ; Q. 
Parry ana, (n. s.) Torrey; Q. Garry ana. Quercus crassipocula is a most interesting species. The leaves are thick and glossy, 
and more like those of the orange tree or lemon than the ordinary oak. The acorns are enormous, and very beautiful. 
