TABLE-HILLS—METAMORPHIC ROCKS. 
13 
It was somewhat flattened as if by pressure. Its outer portions had evidently been bored into 
by worms, as cavities similar to those formed by the Teredo were found filled in with sandstone. 
The whole mass was highly charged with peroxide of iron, which, indeed, seemed to be the 
chief constituent. 
FOOT-HILLS OF THE SIERRA NEVADA, BETWEEN THE MERCED AND MARIPOSA RIVERS. 
We had now progressed so far towards the mountains that we were no longer upon the broad 
plains of the great valley of the San Joaquin, but were travelling among the foot-hills of the 
Sierra Nevada. Our route from this point, southward to Fort Miller, lay nearly on the border 
of the lower granitic ranges, which presented occasional opportunities for examining them, in 
connexion with the sedimentary foot-hills. 
The first outcrop of any of the rocks of the granitic and metamorphic series met on the sur¬ 
vey was near Howard’s ferry, on the Merced. At that place extended outcrops of dark colored 
clay slate were observed, having a trend N. 55° W., and an inclination of 10° towards the 
east. In some places they appeared cliloritic ; and in others had the general character of roof¬ 
ing slate. They were traversed, in the direction of the bedding, by quartz veins of great thick¬ 
ness, the white quartz contrasting finely with the black slate. This place is only nine miles 
west from Quartzburg, where several mining companies have erected crushers and stamps for 
pulverizing the quartz and extracting'the gold it bears. The unconformability of the sedimen¬ 
tary sandstone formation with these roofing and chlorite slates is strikingly shown in this 
vicinity, where streams have cut so deeply as to expose both formations. The horizontal strata 
rest upon the upturned edges of the slates, as is shown in the section. 
