The road from Julian to Stonewall crosses mica schist and gneisses for about half the distance. Then we met outcrops of a dark basic rock, ranging from fine to very coarse texture. It extends southward and covers a large extent of country. The three Cuyamaca peaks, the highest in the southern part of the county, are formed of this rock. This rock was again met about half a mile west of the Stonewall Mine. It extends westward across the mountains for at least 2 miles, and some miles south of the main peak. In places it has a schistose structure. Near the outlet of the Cuyamaca reservoirs it is filled with vein-like aggregates of coarse hornblende crystals, which are probably the result of secondary crystallization in fissures or cracks of the almost consolidated magma. The formation in the vicinity of the Stonewall Mine is biotite gneiss. Toward the east it is not sharply defined from the mica schists. On the west it is generally more granitoid, though at one spot near the lake there are finely laminated schists, dipping 70° southwest. Southward, also, the gneisses become more massive and coarse. At the northeastern base of the main peak a body of coarse granite is partly inclosed in the norite. This norite assumes a dioritic habitus near the granite, with the development of biotite mica. The valley of the Cottonwood was followed down several miles, when it was left and the Morena Valley traversed to its head. The mountains south of the valley are formed of a dark syenite. North and northwest the higher mountains consist of granite, with a great development of mica and hornblende schists along the slope facing the valley. Many granite dikes have been intruded into the schists. North of Mr. Candler’s there is a great dike of pegmatite, carrying small garnets, tourmaline, mica, and large masses of quartz. This pegmatite dike cuts across the cañon, forming a precipice on its lower side. On the upper side the soil has been retained, forming a small but fertile valley. The strike of the mica schists on the north is quite unusual, being north 75° west, dip nearly vertical. Dark syenite lies on the west of this little valley. Morena Valley has an elevation of 3,400 feet. A rough road leads over the mountains west to McClain’s ranch, a distance of 10 miles; the highest point reached having an elevation of 4,000 feet. Near the summit there outcrops a body of coarse eruptive rock, probably a diorite. It consists of coarse hornblendic aggregates in a light-colored feldspathic matrix. This is followed by syenite, and that by coarse white granite as far as McClain’s. The granite about the valley is coarse, with dark, fine crystalline inclusions. It has every character of a truly eruptive rock, even to the minute spaces between the components, left at the time of crystallization. The road now descends to a branch of the Cottonwood, and from the creek there is a long, gradual ascent to the pass north of Lyon’s Peak. The north side of the