490 H. W. TURNER 
Mt. Diablo.) On the south, this serpentine dike is flanked 
chiefly by the rocks of the Golden Gate series. On the north, 
at its east end, it is in contact with the shales of the Knoxville 
formation, and also, at its west end, in the upper drainage of the 
Arroyo del Cerro. At both points, it has effected no appreci- 
able alteration of the Knoxville formation. In the Arroyo del 
Cerro drainage, the intrusive nature of this serpentine is beyond 
all question. The shales here stand nearly vertically with a 
strike in the neighborhood of the serpentine, approximately 
north and south, and a narrow apophysis of the main dike 
extends north into these shales for nearly one mile. This dike 
is cut by the Arroyo del Cerro and smaller streams, and in the 
ravines of these streams the dike nature of this serpentine 
apophysis can be clearly seen. The accompanying geological 
map shows the serpentine dike here described with the narrow 
apophysis extending north into the Knoxville shales. The area 
of the Golden Gate formation (7) in reality includes consider- 
able masses of igneous rocks, chiefly metabasalt and serpentine. 
Thus the north peak is composed of a metabasalt which is said 
by Ransome to exhibit a spheroidal structure. 
The Golden Gate series at Mt. Diablo, as elsewhere, how- 
ever contains large amounts of igneous material which would 
more readily undergo recrystallization than the argillaceous and 
siliceous material of the Knoxville formation. It seems, there- 
fore, possible that any contact metamorphism which the original 
peridotite of the serpentine dike might exert, would show more 
pronounced effects on the sediments of the Franciscan or Golden 
Gate series than on the material of the Knoxville formation. 
In addition to the large dike there are smaller masses of serpen- 
tine at various points along the flanks of the mountain. Glauco- 
phane-schist is found near some of these serpentine croppings ; 
in some cases exactly alongside of them; in other cases, it is 
not at the contact, but forms isolated croppings along with green 
amphibole-schists and micaceous schists. It would be unwise to 
insist that these schists have not resulted from the metamor- 
phism of igneous material, by intrusive igneous masses, but it 
