20 THE MONTHLY BULLETIN. 



journeys of material things in their several cycles than hy recounting 

 to you the bearings on horticultural practice of certain fundamental 

 findings of science gleaned from studies of the cycles of plants and 

 soils, which are, however, not absorbing enough in themselves to be 

 considered a reliable antidote to that tendency to slumber which over- 

 takes most men seated in a nice comfortable lecture hall. However, I 

 am constrained to follow not only the inexorable decree of convention- 

 ality, but also to remain more or less faithful to the implied promise 

 which lingers sadly in the subject of my talk. 



Why We Have Deep Soils in the Arid Region. 



It is a weakness inherent in the human flesh, especially in that of the 

 human of scientific attitude of mind, to attempt the discovery of the 

 underlying causes of things and to try to use these causes as foundation 

 stones upon which to erect the structure which regulates man 's relations 

 with such things. To this weakness the soils scientist is no stranger, 

 and he who has to deal with California soil conditions can not, without 

 paying dearly for his neglect, ignore the cause of the formation of our 

 justly celebrated deep soils which gives us the key to our modern con- 

 ception of rational soil management in the arid region. The institutes 

 and meetings in this State are legion in which I have attempted to 

 expound this interesting fact to which I refer, and yet I have armed 

 myself with the necessary temerity to broach the subject once again to 

 this larger and more representative audience of horticulturists in the 

 hope, which I trust is not vain, that it will bear repetition and may to 

 some here even be wholly new. This important fact to which I have 

 just made such cryptic reference is the manner in which clay is formed 

 and how such clay formation differs in arid and humid regions, the 

 meaning of which terms I shall assume you are familiar with. Clay is 

 largely formed from two of the most common and Avidely spread 

 minerals of the earth's crust, namely potash and soda feldspars which 

 are respectively compounds of aluminum with potash and silicic acid 

 and of aluminum with soda and silicic acid. Now potash and soda in 

 these two feldspars are easily leached out of them under the action of 

 rain and other forms of water which descend upon the earth, the alumi- 

 num silicate being practically insoluble, remaining behind, and that is 

 clay. So that clay constitutes the residues of the feldspars (particularly 

 those named) from the action of weathering agencies. Carrying the 

 argument one step farther it must follow that the largest amount of 

 clay must be formed where leaching and weathering agencies attacking 

 the feldspars of soil material are most active and potent. 



In turn, the leaching and weathering agencies, owing to the large 

 amount and even distribution of precipitation characterizing the humid 

 regions, must be most potent there. Therefore clay must form there 

 most rapidly, and conversely clay can only form slowly in arid regions 

 such as ours, because the leaching agencies are only at work here during 

 a very short period of the year, and even then the total amount of 

 precipitation is usually far below that of the Eastern States which we 

 take as an example of the humid regions. 



