96 CONTRIBUTIONS TO MINERALOGY. [bull. 262. 
The quartz grains are (relatively) fairly large and are not crushed 
like those of the California rock. The rock seems to have undergone 
no dynamic change after its formation. 
The pale-green kyanite has been analyzed by Dr. W. F. Hillebrand 
with the results given below: 
Si0 2 36. 30 
A1A(+Ti0 2 ) 62.51 
Fe 2 3 70 
FeO undet. 
CuO tr. 
Igii 40 
99. 91 
Specific gravity 3.656 at 18.5 
CALIFORNIA. 
This occurrence was first mentioned by Ford, and an analysis of the 
dumortierite was given by him. The writer made a brief visit to the 
locality in the summer of 1903 and collected a large quantity of mate- 
rial, which permitted a rather complete study of the mineral. The 
writer's thanks are due to Mr. John A. Thoman, of San Diego, the 
owner of the property, for permission to visit the interesting locality 
and for the privilege of collecting specimens. 
The mineral occurs in a dike a few miles east of Dehesa, San Dieg< 
County, and is not far from the orbicular gabbro described by Professo 
Lawson/' Tne general country rock of the region is granite, in whicl 
occur large masses of gabbro, of which the orbicular rock is a peculia 
phase. Both the gabbro and the granite contain many dikes, and it i 
in one of these dikes, in decomposed biotite-granite, that the dumoi 
tierite occurs. This dike has a length of about 1,000 feet and a thicl 
ness of about 30 or 40 feet, strikes S. 70° E. , and has a dip of aboi 
70° N. 20° E. 
The rock consists chiefly of quartz and either sillimanite or dumo 
tierite. Feldspar is entirely absent from the dike. The dike may 1 1 
divided into an upper and lower part, according to the character of tl 
rock. The upper part is fine grained and consists of quartz and sill j 
manite; the lower part is coarse grained and consists of quartz ai»| 
dumortierite. 
The upper part, forming about one-half the dike, is a fine-grain' <j 
white saccharoidal rock, sometimes of a grayish color, and never co J 
tains an}^ dumortierite. It possesses a more or less schistose structu ' 
and cleaves off into blocks parallel to the dip. A little muscovite ij 
sometimes present, small crystals of titanium oxide are abundant, a 
occasionally a little pyrite is seen. 
a Bull. Dept. Geol. Univ. Cal., vol. 3, 1904, pp. 383-396. 
