24 ZeConte and Eising— Metalliferous Vein-formation 



wholly of eruptive rocks. The c 

 igneous activity, as of elevation 

 Helena, an ancient volcano 4,313 feet high; but the evidences 

 of former igneous activity continue northward with little 

 abatement to and beyond Clear Lake. In all this region the 

 country rock is largely overlaid with lava, and feeble secondary 

 volcanic activity still continues in the form of hot springs, car- 

 bonated springs, solfataras and fumaroles, or so-called geysers.* 

 In all this region are also found extensive exposures of serpen- 

 tine, and usually, in connection with the serpentine, cinnabar. 

 The origin of this serpentine is an exceedingly interesting 

 question, but one which we are not now prepared to discuss, 

 for immediately about Sulphur Bank the cinnabar is not asso- 

 ciated with serpentine, and it is with cinnabar that we are now 

 concerned. 



Clear Lake vicinity. — Clear Lake is a large irregular sheet of 

 water about 25 miles long, 5 to 8 miles wide, and 1320 feet 

 above sea level, situated about 90 miles north of San Fran- 

 cisco and 40 miles from the sea, in the midst of a very rugged 

 portion of the coast chain. The stratigraphic geology of the 

 region has not been carefully studied. The strata, where- 

 exposed to view, consist of sandstones and shales much dis- 

 turbed and almost destitute of fossils; but according to Whit- 

 nevf they are probably of Cretaceous age. Through these 

 have come up volcanic outbursts, flooding the country and 

 overing the strata. Volcanic peaks, some of them 

 net craters, surround the lake on every side, plainly 

 showing that in comparatively late geological times the lake 

 was belted ab -ut with ;i fn-n /mi!.- of acti\e volcanoes. The 

 loftiest of these is "Uncle Sam," the summit of which is 4200 

 feet above sea level. $ Lava-flows from these volcanoes ran 

 down to the lake margin and into the lake waters, and form 

 now the promontories and islands which diversify its surface. 

 Volcanic activity has now died away into feeble secondary 

 remnants, as hot springs, carbonated springs, solfataras and bo- 

 all of which are numerous in and about the lake. 

 The waters from the last have accumulated to form two small 

 l">rax '.i.-cs. or rather j.ooU, nenr the margin of the greater 

 lake. At one time a considerable tjiiantity of borax was col- 

 lected as crystals from the mud at the bottom of these pools. 

 - geysers or eruptive Bprings depositing 



