THE MAKE OF THE DESERT 



37 



chips and breaks of lava, showing that at one 

 time there must have been quantities of it 

 belched out of the volcanoes. 



There were convulsions in those days when 

 the sea washed close to the bases of the moun- 

 tains. Through the crevasses and fissures in the 

 rocks the water crept into the fires of the earth, 

 and explosions volcanic eruptions were the 

 result. Wandering over these stony tracks you 

 might fancy that all strata and all geological 

 ages were blown into discord by those explo- 

 sions. For here are many kinds of splintered 

 and twisted rocks rocks aqueous and igne- 

 ous, gritstones, conglomerates, shales, slates, 

 syenite, basalt. And everywhere the white 

 coatings of carbonate of lime that look as 

 though they were run hot from a puddling fur- 

 nace ; and the dust of sulphur, copper, and 

 iron blown upon granite as though oxidized by 

 fire. 



The evidence for glaciers is not so convinc- 

 ing. There is no apparent sign of an ice age. 

 Occasionally one sees scratches upon mountain 

 walls that are suspicious, or heaps of sand and 

 gravel that look as though pushed into the 

 small valleys by some huge force. And again 

 there are places on the Mojave where windrows 



Geological 

 ages. 



Kinds of 

 rock. 



Glaciers. 



