GEOLOGY OF THE COAST RANGES. 23 
Mount Harbin, and Uncle Sam are all volcanic. To the east of Clear Lake 
there are to be observed many most interesting phenomena of active volean- 
ism ; hot springs, small lakes holding boracic acid in soiution, sulphur banks, 
and other occurrences of similar origin are well displayed over an extensive 
area of country. So far as our knowledge goes, there is an entire cessation 
of these volcanic phenomena in the region of the Coast Ranges to the north 
of Clear Lake. 
Deposits of gravel of any importance are not usually to be found in the 
portion of the mountains which has just been noticed; but there is one, 
which is quite extensive, in the neighborhood of the north fork of Cache 
Creek, about twelve miles east of Clear Lake. This deposit first shows itself 
at Chalk Mountain, and it extends off to the south, widening in that direc- 
tion, for a distance of ten miles, and occupying a triangular area between 
Lower Lake, Chalk Mountain, and the head of Grizzly Gulch. It is every- 
where stratified, in usually nearly horizontal layers, and is made up of mod- 
erate-sized boulders of the metamorphic rocks occurring in the region, mixed 
with water-worn fragments of unaltered shales and sandstones. This remark- 
able deposit has a thickness in places of as much as 400 feet. No fossils have 
been found in this gravel; but it seems to resemble the Pliocene strata 
already noticed as occurring in the vicinity of San Fernando Pass, and in 
other places farther north. It has been deposited prior to the cessation of 
voleanic action in this region, for a stream of lava coming down from High 
Valley, a little east of the centre of Clear Lake, has flowed over it in one 
place. 
North of the parallel of 39°, as far as the Klamath River, there is much 
monotony in the geological structure of the Coast Ranges. The rocks are 
almost exclusively Cretaceous, and often very much metamorphosed, jaspers, 
serpentines, and even mica-slates, occurring in large quantities, and in the 
most irregular manner; but there are also many areas of quite unaltered 
strata. The topographical features of the country are on a large scale, the 
valleys being deep and precipitous, the ridges lofty and extensive. The 
abundance of chaparral, and the depth of the soil over a large portion of the 
northern Coast Ranges, makes their exploration exceedingly tedious and 
unsatisfactory, and the difficulties of making out the structure are greatly 
increased by the crumbly character of the unaltered strata, and the extreme 
irregularity of the metamorphic areas. It is a constant repetition of jaspery 
belts, imperfect serpentines, and coarse non-coherent sandstones, with ex- 
