chap, i.] SEDENTAR Y SOILS 7 



weakness in the rock become more palpable ; in some 

 cases the joints have been forced open by the intrusion 

 of the roots of trees; minor cracks have started from 

 the main ones, and the disintegration of the rock at 

 the edges of the cracks has proceeded further, till at a 

 distance of 3 or 4 feet from the surface the whole 

 material is loose and shattery, though still preserving 

 the appearance of solid rock. Still nearer the surface, 

 the rock structure seems to have disappeared ; rock 

 may be there in lumps and fragments, but it is em- 

 bedded in small material that may fairly be termed soil 

 or earth. Still nearer the surface the rock fragments 

 become smaller, and the proportion of fine earth larger, 

 till in the top 9 inches or so a new change begins. 

 Here the stones are generally small, and the material 

 is dark from the admixture of decaying vegetable 

 matter, residues of the crops that have covered the 

 surface for long ages. This is the soil proper, generally 

 shading gradually into the subsoil below, which in its 

 turn passes insensibly into the underlying rock. It is 

 obvious that a soil such as we have been describing has 

 been directly formed from the rock — it is, in fact, the 

 rock disintegrated and reduced by frost and snow, air 

 and rain; all those agencies we group together under 

 the name of "weathering." We are dealing with a 

 soil formed in situ, or, as it is sometimes termed, a 

 sedentary soil. 



The frontispiece shows a photograph of such a case 

 of weathering of rock into subsoil and soil, as seen in a 

 section of the Hythe Beds, near Great Chart, Kent. 



But when we examine the section of the gravel pit 

 or the brick earth workings lower down in the valley, 

 the sequence is not the same ; we still have the soil 

 proper passing into the subsoil, but this is fairly uniform 

 throughout instead of showing a progressive change 



