336 RESOURCES OF CALIFORNIA. 



Mount Lassen also vomited wonderful quantities of molten 

 rock; and an area of nearly, if not quite, 10,000 square miles, 

 including those two peaks, is covered with lava of various 

 kinds, and in many places they have net been sufficiently 

 decomposed on the surface to sustain a good growth of vege- 

 tation. 



262. Extinct Volcanoes. The most southerly volcanic 

 peak yet discovered on the Coast is Mount St. Helena, in 

 latitude 38 42', 4,343 feet high. Its volcanic origin is 

 indubitable, although its long and flat form does not suggest 

 the volcanic idea to the spectator looking from a distance. 

 The basaltic columns forming a projecting point at its north- 

 ern end, and another, but less prominent one, near its southern 

 end, and the basalt covering the ridge to the southward, must 

 have come from this crater, which was once half a mile in 

 diameter, but has been worn down by the eroding action of 

 water, so that its original outline is scarcely traceable. The 

 ridge between Sonoma and Petaluma is covered with trap ; 

 that between Napa and Sonoma has an immense quantity of 

 tufa and a little trap, and that east of Green Valley in Solano 

 County has much tufa; and presumptions indicate that all 

 these may have poured out from St. Helena. The country, 

 however, for fifty miles north-northwestward from St. Helena, 

 is full of the evidences of great volcanic activity. Clear 

 Lake, which is twenty miles long, seems to have been the 

 crater of a volcano, and the Californian Geysers are solfataric 

 in their character, and undoubtedly derive their heat from the 

 deep internal fires. 



263. Gold-bearing Rocks. The gold-bearing formation 

 of California is a j urassic slate, in which are found veins of 

 auriferous quartz, and these occasionally extend into adjacent 

 granite and limestone. The erosion or disintegration of the 

 rock has set free much gold, which is now found in the placers 

 or gravel beds. 



The quartz lodes vary in thickness from a line to forty feet, 



