1854.] WILSON — CALIFORNIA GOLD-FIELDS. 319 



tion with regard to the hills, being deepest and richest at the open- 

 ing of the ravines, and in the middle of depressions. It is a tough 

 whitish clay, intermixed with petrified wood and fragments of quartz 

 and other rocks. The bed-rock is a coarse-grained slate, with crystals 

 of felspar (like that of many other places) . The rock was decomposed 

 to a considerable depth, forming a clay that could only be distin- 

 guished from the best auriferous earth that lay on it by not having a 

 mixture of quartz-gravel. 



I found a small vein of asbestos in this rock that is similar to a 

 specimen that I had obtained from Van Diemen's Land, attached to a 

 fragment of similar rock. 



Mokelmne Hill Diggings. — At Mokelmne Hill I found extensive 

 remains of the tertiary 1 formation above-mentioned, under which 

 mines of extraordinary richness were being worked, at great depths. 

 This description of mine is known to miners by the general designa- 

 tion of " volcanic diggings," probably because the upper stratum of 

 the series consists of volcanic cinders cemented with lime. See Murphy 

 Creek Diggings, p. 316. 



Volcanic Cinders. — The presence of these volcanic products is oc- 

 casionally the cause of much speculation, no volcanos being known 

 to exist in California, nor traces of any that could have been of such 

 late origin. The course of the prevailing winds, and general drift of 

 the Northern Ocean, might, however, lead us to look for their origin 

 in the volcanos of Kamtschatka and the Aleutian Islands. 



General Geology of the Region. — Having examined the country 

 from the Mokelmne to near the Mariposa, and obtained information 

 from others who had travelled farther north and south, I am enabled 

 to state that apparently the same arrangement of the strata prevails 

 throughout the range, and a section at right angles to the line of 

 the strata at one point will represent the general order of the rocks. 

 (See Map and Section, figs. 1 & 2.) If, therefore, a section be taken 

 from the granite hill east of the town of Sonora, and drawn in a 

 line to the Valley of the San Joaquin at a point near to Taylor's 

 Ferry, the arrangement is — 1st, gneiss ; 2nd, white crystalline lime- 

 stone ; 3rd, mica-slate ; 4th, chlorite-slate ; 5th, a coarse slate, con- 

 taining much felspar ; 6th, clay-slate. These all stand vertically 

 and parallel with the mountain-range, and are traversed by three 

 principal quartz-veins, running in the same direction, from east of 

 south to west of north. The first or eastern vein is in the gneiss, 

 but near to the line of the limestone. The second or middle vein is 

 in the mica-slate, but close to the chlorite-slate, and sometimes di- 

 vides or passes between them ; the third is in ' the coarse slate, but 

 not so well-defined as the other two. 



The Tertiary Rocks. — The tertiary? limestone formation has been 

 very extensive. Its ancient margin may still be traced in places, 

 occurring in boulder-conglomerate cliffs, attached to the sides of the 

 hills formed by the older rocks, about 4000 feet above the level of 

 the sea, and from 200 to 300 feet above the streams in the adjoining 

 valleys. The remains of this formation abound in the neighbour- 

 hood of the Calaveras and Mokelmne. It has penetrated the 



