184 University of California Publications in Geology [Vol. 13 



thick, of biotite and sillimanite. The sillimanite is in prisms, generally 

 about 4 mm. in diameter and as much as 1 cm. in length. The tour- 

 maline is pleochroic in brown colors, thus differing from that found 

 in the pegmatite of the Friday Mine, whose colors, under the micro- 

 scope, are steel-blue and gray-blue. 



Sillimanite gneiss much like the above, except that it carries no 

 tourmaline, was found as far as one-quarter mile from the nearest 

 quartz-diorite outcrop along the line between sections 9 and 10, and 

 in the northeast quarter of the northwest quarter of section 10, town- 

 ship 13 south, range 4 east. Along the western margin of that part 

 of the main schist belt lying southeast of Cuyamaca Reservoir silli- 

 manite gneiss was found at least one-half mile from the nearest out- 

 crop of granitic rock. 



A typical specimen of andalusite-bearing gneiss, collected about 

 three-quarters of a mile east of the quartz-diorite contact, in the main 

 schist body east of Cuyamaca Reservoir, is composed of quartz, bio- 

 tite, labradorite, and andalusite. The biotite is for the most part 

 segregated in thin layers, which are much contorted. The andalusite 

 is in prismatic crystals, pink in color. 



A specimen from the main schist body two miles southeast of 

 Julian has the same mineral composition, except that the feldspar is 

 oligoclase. This specimen also has much of the biotite segregated in 

 thin layers, separated by granular layers, up to 3 mm. in width, poor 

 in biotite. There is no contortion, however, the rock being evenly 

 banded, though not fissile. 



A third specimen, from a point on the Julian-Banner road, one- 

 half mile east of Julian, is a fine-grained quartz-mica schist, carrying 

 crystals of andalusite. 



The three rocks seem to be the result of successively less severe 

 degrees of metamorphism of the same kind of original material. 



Injection gneiss. — The sillimanite gneisses and many of the anda- 

 lusite gneisses seem to be made up in part of material of igneous or 

 pegmatitic nature. They might be classed under injection gneisses. 

 But injection gneisses in which no sillimanite or andalusite occurs, and 

 in which the igneous material varies from small amounts up to nearly 

 the whole of the rock, are found along all the contacts between schist 

 and quartz-diorite gneiss. 



An excellent place to study injection gneiss is on the Julian- 

 Banner road, two miles east of Julian. For a distance of about one 

 hundred yards southwest of the igneous contact the fissile schist is 



