248 ANNUAL REPORT OF THE Off. Doc. 



whicli is close, compact, little soluble and easily washed away. The 

 native shale soils are usually stubborn. Their compactness pre- 

 vents percolation of ground waters, retards the process of soil mak- 

 ing, and therefore requires more careful treatment than is desirable. 

 Without rational treatment, they are totally incapable of support- 

 ing ordinary field crops, though fruit trees and forest thrive well 

 upon them. 



As these three are the only varieties of rock, furnishing several 

 grades of soil, analysis may be adduced to show that the plant foods 

 which they contain are ample in amount; but they require the ac- 

 tion of other agencies to render them arable and capable of bearing 

 ripened vegetation to the highest degree. Of the 4,500 tons of water 

 falling upon every acre of the surface of the earth, a large propor- 

 tion enters the soil as an effective element of food as a medium for 

 transporting the nutrition and as an important and physical agent 

 in cultivating the soil, while the larger amount is lost by imme- 

 diately passing from its surface, carrying with it such fine material 

 as is capable of transportation. 



We shall see presently the necessity for restricting the amount 

 of this surface wash ; meanwhile, let us consider what is transpiring 

 below the surface. The rain in its descent through the atmosphere 

 dissolves from the atmosphere the all-powerful carbonic acid, which 

 decomposes the organic matter in the earth and produces what we 

 choose to call humus. This has the property of absorbing moisture 

 and soluble substances, and also, with the oxygen of the air, of act- 

 ing as a reducing agent to fix many of the uecessarj^ compounds of 

 plant food. When these waters enter the soil they are capable of 

 circulating through it according to its capillarity, and the degree 

 of capillarity is determined by the fineness of the earth. A coarse 

 sand has little capillarity and will not restrict, the free descent of 

 waters. It is therefore incapable of retaining much of the moisture 

 that enters during the rains and long before the drought ends will 

 have disappeared. Little benefit accrues to shallow rooted crops 

 and the soil becomes irreparably exhausted. Limy soils are quite 

 dense, have a medium degree of fineness and of absorption. A finely 

 decomposed clay has a high capillarity and a power of imbibing 

 fifty per cent, of its volume of water. A soil which is exceedingly 

 close, like a native shale soil, does not permit much circulation of 

 the rains and their soluble contents, but it sheds the waters which 

 are soon lost in the sea. Only a medium soil containing a proper 

 mixture of clay and sand is capable of circulating the solvent waters 

 without allowing too much to descend. This happy medium may be 

 procured by natural processes of mixture or by our artificial pro- 

 cess of cultivation. Those waters which have entered the crust of 

 the earth have disappeared beyond reclaim. They are not within 



