32 AGRICULTURE ON THE PACIFIC SLOPE 



bacteria (page 250) make leaf mold and finally humus 

 of them. Naturally this makes a dark surface soil. 



In the arid states the leaves do not fall so regularly, 

 and they are mostly smaller and fewer, and cannot 

 make a thick cover on the ground. When they fall 

 in open ground during the dry summer and autumn, 

 they are blown about by the wind and torn to shreds, 

 which are mostly dry-rotted and slowly burnt up by 

 the sun before the rains come. So it often happens 

 that even at the very surface of the ground there is 

 very little humus, so that the soils look gray or white. 

 It is only in low, moist places and hollows that enough 

 leaves drift together to decay and form leaf mold. 

 We also find leaf mold in the shade of the dense cha- 

 paral on the northern slopes of hills where the sun and 

 wind do not reach. 



Thus there is usually in California, and in most of 

 the arid states lying west of the Rocky Mountains, 

 little or no difference between soil and subsoil, outside 

 of swamp and marsh lands. The farmer can plow as 

 deeply as he pleases without bringing up raw, yellow 

 subsoil unfit for the seed bed. He often has as many 

 feet of soil as the Eastern farmer has inches, and (as 

 will be seen later) his soils are as a rule much richer in 

 food for the plant. 



On all high mountains the rainfall (and snowfall) is greater 

 than at their foot. Mountain climates are largely humid, 

 as in the high portions of the Sierra Nevada, and of the 



