SOILS AND THEIR COMPOSITION 165 



bursts of volcanic forces have had their say in the matter, 

 Section No. 2 gives us a much truer view of what we should 

 find if we turned geologist and paid a visit to some escarp- 

 ment, sea clifi, or quarry cutting to-day. (See Plate 38.) 

 It will at once be seen that the effect of the cracking 

 up and doubling over of the various strata is to give 

 variety to the surface which it would not otherwise have 

 had, besides lending the geologist enormous aid in bringing 

 up strata which he could not else have observed without 

 very great difficulty. It will also be seen from the sketches 

 that the top layer is the same in each case, and is called 

 " drift." This is made up of materials, small fragments 

 of rocks, distributed by such minor forces as glaciers and 

 the action of rainwater and frost, the wearing down or 

 denudation by rivers and the depositing of the scoured- 

 away material in other places, and this drift process has 

 given the top surface of the present world a further 

 alteration of character. 



In Section No. 3 we may observe the whole process, 



where (a) represents the parent rock, (6) the subsoil 



formed partly of decomposed fragments of the rock and 



partly of drift deposits. In the course of time this 



subsoil affords a home for innumerable generations of 



plants and animals, which, by their hfe and death and 



the admixture of their remains "with it, are constantly 



forming (c) which we call the top soil. The shading 



between the top soil and the subsoil, marked (t) represents 



what is called the "water-table," i.e. the general level 



to which surface water percolates, and at which it drains 



away to lower land and finally to a river basin. If this 



water-table is too near the surface, the roots of plants 



will be injured by the damp sour soil, and thus growth 



will be checked. Hence deep digging will place the 



l^^srater-table out of harm's way, besides aerating the soil 



mpid dispersing the stagnation. Should the land be 



^neav}'-, proper drainage must be ensured by the laying 



of soil pipes, the effect of which will be to make the 



tf 



