’ 
ROCKS OF THE COAST RANGES OF CALIFORNIA 489 
part at least, to contact metamorphism, and not regional meta- 
morphism, believing that Dr. Ransome has established this in 
his bulletin on Angel Island. Professor Lawson seems to me to 
state the case very fairly. He writes as follows: 
‘In some few cases the schist areas have a very definite 
relation to dikes and laccolitic lenses of serpentine, and some 
of the most highly altered phases of schist that have been 
found, both of the micaceous and the blue amphibole varieties, 
have been taken from the immediate contact with the serpentine. 
In these cases there seems to be little doubt that we are dealing 
with a contact zone. In other cases, however, we have the 
immediate contact of serpentine and sandstone well exposed 
with no perceptible development of schist at the contact and 
little alteration of any kind appreciable to the unaided eye 
beyond a narrow zone of hornfels. It seems clear, therefore, 
that the metamorphic action of intrusive peridotite upon the 
rocks which it invades is not uniform, and the conditions 
which determine in some cases a Maximum and in some cases a 
minimum of metamorphism are not yet known.” 
The point Lawson makes, that serpentine in many cases has 
merely hardened the sediments into which it is intruded and 
has not metamorphosed them, is perhaps of vital importance in 
discussing the origin of these schists. Inthe case of granitic 
intrusions into sediments, as everybody knows, there is always a 
zone of metamorphism all around the mass, and the conclusion 
that the granitic rock has caused this metamorphism appears to 
be absolutely demonstrated. When, therefore, we have an 
igneous intrusion which is bordered by schists on one side and 
by little altered sediments on the other, and if we know the 
latter to be older than the igneous mass and intruded by it, it is 
difficult to imagine conditions which cause such variable effects 
if we ascribe the formation of the schists to contact metamorphism. 
Such a case may be finely seen at Mt. Diablo. Here a dike of ser- 
pentine about 6.6*™ long and 800™ wide extends in an east and 
west direction from the north flank of the mountain to near the 
east fork of Pine Creek. (See the geological sketch map of 
