102 Adventures in Scenery 



outpourings of molten rock during Archaean and throughout 

 Palaeozoic time, but these should be regarded probably as 

 poured out of fissures rather than ejected from true volcanic 

 vents (cones) . 



Recent Volcanic Activity 



The volcanic activity which has built up Lassen Peak, Mt. 

 Shasta, and many cones or peaks of this great lava field is com- 



Photo by J. S. Diller. Courtesy Unii. of Calif. 



FIG. 29. Chaos Crags, viewed from north slope of Lassen Peak. 



paratively recent. Probably the greatest outpouring of lava 

 was at the time when the great Sierra Nevada range was finally 

 uplifted to essentially its present height, which was in early 

 Quaternary time. Volcanic activity in this region of Califor- 

 nia has continued till the present time and is today marked by 

 the presence of numerous solfataras, hot springs, and geysers. 

 At Bumpass Hell near the southern base of Lassen Peak are boil- 

 ing mud pools and fumaroles with escaping sulphurous gases. 

 Nearby sulphur deposits have been sufficient so that attempts 

 at commercial mining have been made. Most of the major vol- 

 canoes are of such recent origin that their forms have scarcely 

 been modified by erosion. 



