370 QITICKSILVEII DEPOSITS OF THE PACIFIC SLOPE. 



Helena and covers large areas to the north, east, and southeast of that 

 mountain. The summit of Mt. Cobb is also andesitic. Tufaceous forms of 

 andeslte, usually much decomposed, are also abundant, especially to the 

 south. 



At the southern end of Mt. St. Helena there are argentiferous quartz 

 veins in andesite from which a considerable amount of ore and, it is said, 

 $90,000 of bullion have been extracted. About one and a half miles north 

 of Calistoga, in King's Canon and on a small ridge to the north of it, there 

 are argentiferous quartz veins in andesite. Two of these strike northeast 

 and southwest and two others cross them, striking nearly north and south. 

 One of these latter is called the Elephant and carries ore of great interest, 

 both cinnabar and pyrargyrite being visible in it, as well as pyrite. The 

 cinnabar was chemically tested and the silver ore was analyzed. The latter 

 contained antimony, with a mere trace of arsenic, sulphur, silver, copper, 

 and a trace of lead. Here, then, is a true vein, carrying almost precisely 

 the same ingredients as the deposits of Steamboat Springs. This is also the 

 only case known as yet on the Pacific slope, excepting Steamboat Springs, 

 where lead and quicksilver occur togetlier. This vein is certainly a com- 

 paratively recent one, for the greater part of the andesites of the region are 

 Post-Pliocene. In ore from one of the other veins (the Grigsby) cinnabar 

 and pyrite were found together. 



Large quantities of basalt were erupted at a much later period than 

 that of the andesites. It occupies large areas to the north of Oathill and the 

 igneous region east of Middletown is mostly basaltic. Some of the rock 

 last mentioned produces a marked effect upon the needle and contains much 

 magnetite. In some cases andesitic hills are capped by basalt. There are 

 immense quantities of tufa to the southeast of Mt. St. Helena, and embed- 

 ded in it are fragments of compact l)asalt, showing that the tufa belongs to 

 the basaltic series of eruptions. The tufii is especially abundant in the 

 neighborhood of the North Cone and South Cone and it often forms dis 

 tinctbeds, which are sometimes considerably inclined. It not infrequently 

 includes great quaiitities of metamorphic pebbles. 



The drainage and triangulatlon of the accompanying sketch 7nap are 

 mainly cniniiilcd i'loiu surveys by ^Ir. C. F. IlnfTnianii, but this material lias 



