MARYLAND WEATHER 



plants thin, consists first in the soluble food substances which they 

 contain, and second in the manner in which they make available id 

 plants the water which climate and topography bring within the 

 sphere of control of tbe soil itself. 



The principal hulk of soils is made up of rock particles ricb in 

 difficultly soluble salts of aluminum and silicon. It is to the insolu- 

 bility of these salts, in fact, that their predominance is due. Soils 

 owe their origin to tbe weathering of rocks and to tbe gradual disin- 

 tegration and pulverizing of the rock fragments by the action of 

 frost, rain, etc. The rapidity with which a particular sort of rnck 

 may be weathered to soil, and the degree of fineness to which its 

 ultimate particles will be reduced depends upon the mineralogical 

 character of the rock. In regions where rocks have been exposed to 

 tbe atmosphere for a very long time we will find overlying each rock 

 formation tbe particular sort of soil to which it gives rise, as is the 

 case throughout almost the whole of Maryland to the north and west 

 of the "Fall-line." In the Coastal Plain the soils are derived from 

 materials which have been transported by streams from the eroding 

 upland and laid down in the floor of a shallow ocean. These facts 

 point to a distribution of soils in the Midland and Mountain Zones 

 of Maryland which is closely parallel to the distribution of the 

 various rock formations. The fact that the soils became inhabited 

 by plants very early in their origin is not only important in its re- 

 lation to their further weathering but also to the admixture with 

 the rock particles of minute fragments of organic matter, — the 

 humus. Tbe interstices between the particles of rock and humus 

 may be completely tilled with air or completely filled with water. 

 Under average natural conditions in upland soils the interstices arc 

 partly tilled with water, which adheres by capillary attraction to 

 tbe surfaces of the rock particles or accumulates in the acute angles 

 formed by the contact of adjacent particles or is held by imbibition 

 in the humus particles. 



In a review of the characteristics of the soil it is necessary to dis- 

 tinguish between those that are chemical and those that are physical, 

 between such features on the one hand as the chemical nature of the 

 rock particles or the amount and state of the humus, or, on the other 



