THE SOIL, HOW MADE, AND FROM WHAT 23 



grow on the volcanic ash. These after a time give 

 way to still higher plants, such as stonecrops ("hen- 

 and-chickens"), aloes, and such other plants as need 

 but little soil or moisture. By the root action of these 

 the soil is gradually increased and deepened, until 

 shrubs and trees find foothold and flourish in the vol- 

 canic soil. The vine, olive, and fig are among the first 

 crops that can be successfully grown on such soils. 



In the mountains of the Pacific Coast many examples of 

 this can be found. Volcanic-ash 'soils are common both in 

 the Sierra Nevada and. the Cascade Mountains, and in the 

 Coast Ranges. Such soils are found in California near Coif ax 

 and Grass Valley, and southward on Calaveras and Kings 

 rivers. We find them in the Coast Ranges in the Napa and 

 t Sonoma valleys, where wine cellars have been dug into vol- 

 canic ash which has hardened into a soft rock. They are 

 also found southward in the petroleum region; much of the 

 soft white rocks from under which the oil comes, are largely 

 composed of volcanic ash, mixed with minute fossil shells. 

 Similar deposits and soils are found on the flanks and in the 

 valleys of the Cascade Mountains in Oregon and Washington, 

 as on the Willamette, and on the plains eastward of Mounts 

 Hood, Adams, and Tacoma, where the winds have carried the 

 ashes. 



Most of the soils now cultivated in the Hawaiian Islands 

 are made from decayed black lava or from volcanic ash. 



With solid rocks the process is the same, only they 

 must decay at least on the surface, before the bacteria 

 and lichens can settle on them. We see this in our 



