84 THE ORIGIN AND NATURE OF SOILS [chap. 



fundamental rocks covered, often to a considerable 

 depth, with disintegrated rock that has been moved into 

 its present position by the action of ice in the imme- 

 diately previous geological epoch, when a glacial climate 

 prevailed. These glacial drifts, as they are called, may 

 be mainly clay or sand, but usually they are considerably 

 mixed with fragments of rock of all kinds and sizes — 

 fragments which give clear evidence of the actions they 

 have been subjected to among the moving ice by the 

 way they have been rounded off and scored with 

 scratches and furrows. These glacial drifts form an 

 exception to what has already been said as to the 

 general uniformity of the transported soil material. 



All soils derived from material that has not grown 

 up from the rock below, but has been moved by water, 

 wind, or ice, are known as " soils of transport " or " drift 

 soils," in contradistinction to the sedentary soils first 

 discussed. Some idea of the constant state of motion in 

 which soils still exist may be obtained by considering 

 the surface of an arable field on such soils as the chalk, 

 where there are a good many stones. The stones are 

 always much more abundant upon the top than in the 

 layers below; they may not be very prominent when 

 the surface is turned over by the plough, but they 

 work up again ; they may even be picked off to sell 

 for road-making, yet in a few years they seem as 

 numerous as ever, so that the older farmers and 

 labourers declare they "grow." The clue to their 

 abundance upon the surface may be obtained by 

 looking at any garden bed where it happens to receive 

 the drip from the eaves of a building; the constant 

 downpour of water washes all the soil away, and leaves 

 the ground covered with small stones. The same action 

 goes on in the stony mixture constituting the soil of the 

 arable field; with every rainfall there will be some 



