Swe 
GRAVEL AND VOLCANIC FORMATIONS: AMADOR COUNTY. 127 
extremely difficult to refer any portion of it to its original source in the High 
Sierra. The region near Q. Ranch, a few miles northwest of Ione City, 
shows a number of these isolated mound-like outliers of volcanic sedimentary 
deposits. One of these elevations, called Pratt’s Hill, four or five miles west 
of Ione City, is made up of a series of strata of clays of different colors and 
textures. There are five of these beds, which seem to have been formed, in 
large part, from the trituration of the débris of volcanic materials, resting hori- 
zontally on the bed-rock, which is here a hard, compact, fine-grained silicious 
slate, somewhat ferruginous in character. On the clay beds is a deposit of 
coarse gravel, made up almost exclusively of well-rolled pebbles of lava. This 
is succeeded by a fine gravel cemented by volcanic sand, and capping the 
whole a solid (andesitic ?) lava. 
The volcanic deposits cover a large amount of surface in the vicinity of 
Jackson, which town is situated upon the slates, but is surrounded by an 
almost continuous line of elevations capped with volcanic materials. Large 
areas to the south and southwest of the town have been washed off and 
found rich in gold. North of Jackson and extending along the south side 
of Sutter Creek is a continuous ridge of lava, known as Humbug Hill. 
The thickness of the detrital deposits here is about 250 feet; of this, about 
200 feet consist of finely stratified materials, and the upper fifty of imper- 
fectly rounded masses of lava (andesite ?) which grow larger towards the top 
of the stratum. The thickness of the pay-streak is quite small, in places not 
over one or two feet, and it is made up chiefly of pebbles and slightly rolled 
fragments of quartz, including, however, some very large boulders of the 
same. The channel is said to be about 125 feet in width. 
The “ Butte,’ about four miles east of the town of Jackson, is an isolated 
knob, from which a fine view of the adjacent region may be had. The sum- 
mit is elevated about 1,200 feet above the town of Jackson, and 800 feet above 
its base. At the base of the Butte, on the west side, an excavation made by 
prospecters shows horizontal strata of white clay, sand, and finely powdered 
pumice-stone, the thickness of which could not be ascertained. Above this 
apparently horizontally stratified and undisturbed sedimentary volcanic de- 
posit is at least 500 feet in thickness of a hard eruptive material of a reddish 
color, supposed to be basaltic in character.* This mass is distinctly lami- 
nated or stratified, and the layers have a variable strike and inclination. 
The prevailing direction, however, is northeast and southwest, and the dip, 
which is very irregular, is in places as much as 50° or 60°. 
* The specimens obtained in this vicinity were all destroyed by fire. 
