CRVSTALLINE ROCKS OF OAK HILL AREA 167 
faces were observed on many crystals. The cleavage parallel to the 
prism is perfect with angles of about 124.° 
The lawsonite crystals are comparatively fresh and occur in con- 
siderable quantity. A good outcrop of this rock is found near the 
present workings of the San Juan mine. 
2. The garnetijerous schist——The chief difference between this and 
the typical schist is the relatively smaller amount of glaucophane, the 
development of numerous garnets, and a somewhat less marked 
schistosity, the rock being more massive. The garnets, which are 
irregularly distributed throughout the rock, average about one milli- 
meter in diameter, and can often be detected with the unaided eye. 
The mica flakes, which are also unevenly distributed, are small, 
but very numerous. It has been mentioned as eclogite by Mr. R. S. 
Holway.? 
The microscope reveals the presence of much garnet and chlorite, 
some lawsonite, actinolite, glaucophane, and usually also white mica. 
The garnets usually appear in well-defined crystals, showing high 
index and high relief. The individuals are nearly always strongly 
fractured and the cracks filled with green chlorite. In ordinary light 
the garnets are light reddish-brown in color. ‘The lawsonite is scarce 
in this rock, appearing as small weathered patches. The green 
chlorite occurs in abundance in rough, irregularly shaped patches. 
The glaucophane is not abundant; it, occurs as small blue prismatic 
crystals with properties as described in the typical schist. The mica, 
like a garnet, is unevenly distributed through the rock. It is of a 
slightly brownish tint and is probably paragonite. 
3. The acid or quartz-bearing schist—The most highly acid 
exposure of this type of schist was found in close proximity to highly 
altered banded jaspers in which the typical features, including the 
banded structure, had disappeared, and the rock was identified only 
by the presence of radiolaria as shown by the microscope. 
The schist is massive and made up almost entirely of silica in 
indistinct bands of variable thickness, with a little mica on the sur- 
faces. ‘Lhe microscope, however, shows in the slide here and there 
a deep blue prism of glaucophane imbedded in the silica, and innu- 
merable minute pink dodecahedral garnets. 
« “Kclogites in California,” Journal of Geology, Vol. XII, No. 4. (1904), p. 354. 
