BEDS OF MAGNESITE—GRANITE—TRAP-DIKES. 
29 
abound on the banks of Moore’s creek, and very little oak timber was seen. The river bed is 
shallow and sandy, and it was evident that the stream is sometimes greatly increased in volume. 
On the hanks of a dry creek, six and a half miles south of Moore’s creek, there is an outcrop 
of a brownish magnesian rock, trending northwest and southeast, filled with seams and veins 
of translucent quartz, resembling chalcedony. It is probably a formation similar to that 
occurring northward of Four Creeks, already mentioned. 
A short distance beyond this exposure of rock, the hills on the left appear to be formed of 
trappean rocks, and at the crossing of a small creek I found an outcrop of compact trap rock, 
OUTLIERS OF GRANITE, NEAR WHITE CREEK. 
of a dark-green color and fine grain. The weathered surfaces were clear and smooth. The 
apparent trend of this intrusive rock was north 30° west, magnetic. 
After passing Tule creek, we left the plain, and travelled among the low foot-hills of the 
Sierra. Two or three miles north of White creek, we came upon the edge of the granite forma¬ 
tion, and the rock makes its appearance on the surface in a succession of long and narrow out¬ 
crops, from twenty-five to fifty feet in width, standing like walls on the gently undulating 
ground. They were of sienitic granite, but were undergoing rapid decomposition, weathering 
into rounded masses. The trend of the principal outcrop was N. 60° E., (very distinct,) dip 
N. SO 0 -^ 0 . 
Not half a mile beyond this place, the direction of trend changes suddenly to N. 20° W., 
(nearly at right angles with the former,) and the dip is eastward. The rock rises above the 
surface in similar lines, but forms a higher ridge on the left; the summit of which I found to 
consist of an intruded igneous rock, of compact structure and light color, breaking or cleaving 
up with great facility into large or small rhomboidal blocks, showing the mass to be in a con- 
