I 9 4 THE BOOK OF NATURE STUDY 



and uniformity of the glacial deposit whether the soils formed 

 from them shall be termed sedentary or soils of transport. Other 

 true "soils of transport " are wind borne, though almost the only 

 examples we see of them in this country are the soils that have 

 grown up on the inland side of the tracts of sand-dunes which border 

 some parts of the coast. A peat bog, though entirely unlike the 

 strata upon which it may be resting, has yet been formed in situ, 

 and must be classified as sedentary. The causes which lead to such 

 a formation will be considered later. 



It is, in fact, impossible to draw any entirely satisfactory line 

 of distinction, for soils, however sedentary they may be in their 

 origin, are always in motion, and often in the end acquire the 

 character of soils of transport. As an example it is instructive to 

 compare two neighbouring fields, one arable and the other old 

 pasture, on any soil where stones are abundant, as, for example, 

 on the chalky soils of the south and east of England or the boulder 

 clayland of the north and midlands. The arable land will be 

 seen to be covered with stones, and even if they have been worth 

 picking off they are as abundant as ever soon afterwards, until 

 the old farmers aver that they "grow." In reality, the soil 

 is being constantly stirred by the plough, and as the soil 

 settles down again the washing rains carry down the fine 

 particles and leave on the top the stones they cannot move. 

 You have only to look at some spot where a water pipe drips 

 on to a bed of bare soil to understand how on arable land the 

 stones are always working to the surface. 



On the old pasture alongside not a stone is to be seen, and if a 

 trench be cut, the surface soil of the pasture will be found to be 

 fine mould free from stones, down to a depth depending upon the 

 age of the pasture. Yet the arable land and the pasture started 

 alike, it is the action of the earthworms that has gradually brought 

 the stones below the surface of the pasture land. Earthworms are 

 always at work bringing up fine soil from below and ejecting it in 

 the form of worm-casts on the top of the present surface, and 

 small as the amounts brought up may seem to be, the action is 

 yet so continuous that when the casts are spread over the surface 

 the layer raised each year possesses a measurable thickness. In 

 this way stones and any other objects lying on the surface of 



