14 THE MOUNTAINS OF CALIFOKNIA 



fast for ages, have suddenly blazed into violent ac 

 tion, and poured forth, overwhelming floods of fire. 

 It is known that more than a thousand years of 

 cool calm have intervened between violent erup 

 tions. Like gigantic geysers spouting molten rock 

 instead of water, volcanoes work and rest, and we 

 have no sure means of knowing whether they are 

 dead when still, or only sleeping. 



Along the western base of the range a telling 

 series of sedimentary rocks containing the early 

 history of the Sierra are now being studied. But 

 leaving for the present these first chapters, we see 

 that only a very short geological time ago, just be 

 fore the coming on of that winter of winters called 

 the glacial period, a vast deluge of molten rocks 

 poured from many a chasm and crater on the flanks 

 and summit of the range, filling lake basins and 

 river channels, and obliterating nearly every exist 

 ing feature on the northern portion. At length these 

 all-destroying floods ceased to flow. But while the 

 great volcanic cones built up along the axis still 

 burned and smoked, the whole Sierra passed under 

 the domain of ice and snow. Then over the bald, 

 featureless, fire-blackened mountains, glaciers be 

 gan to crawl, covering them from the summits to 

 the sea with a mantle of ice; and then with in 

 finite deliberation the work went on of sculptur 

 ing the range anew. These mighty agents of ero 

 sion, halting never through unnumbered centuries, 

 crushed and ground the flinty lavas and granites 

 beneath their crystal folds, wasting and building 

 until in the fullness of time the Sierra was born 

 again, brought to light nearly as we behold it to- 



