166 Clement Reid — On Dud and Soils. 



commonly contain constituents unknown in the subsoil — not only- 

 organic constituents obtained from the air or rain, but abundance of 

 inorganic substances. Those who have been obliged to pay much 

 attention to soils and superficial deposits are well aware how often 

 the soil does not show what lies underneath. In districts where 

 sections are scarce this has been found one of the greatest of the 

 difficulties in the way of an accurate survey. Time after time dis- 

 tricts with a distinctly loamy soil have had to be mapped as sand, 

 and still oftener a thin sandy soil overlies clay. Often these anomalies 

 may be accounted for by rain- wash from higher levels ; but during 

 the examination of large areas in Holderness and Norfolk, I have 

 been much struck by the curious fact that not only is there a fertile 

 soil over large raised tracts of sand and gravel, but even isolated 

 sand hills have also a loamy soil. This fact is often overlooked, for 

 soils are seldom more than a foot or two thick, and the character of 

 the vegetation largely depends on the nature of the subsoil. A thin 

 soil, which if deep would be wet and clayey, if it rest on sand 

 becomes well drained or even parched ; whilst a sandy soil lying on 

 clay may be perfectly waterlogged. Trees are of little value as 

 evidence of the nature of the surface soil, for their roots generally 

 penetrate deeply into the underlying subsoil, where quite difi"erent 

 conditions may exist; this, however, makes them much more useful 

 than shallow-rooting plants as indications of the geology. 



A particularly good example of the non-correspondence of the soil 

 and subsoil is seen in the Chalk Wolds and Downs ; for the com- 

 position of the Chalk is so simple that the transported material in 

 the soil can be at once detected. Besides this neither the Wolds nor 

 Downs are, or have been, commanded by higher ground from which 

 the material could be washed. It is necessary, however, to confine 

 ourselves to areas over which Boulder Clay stones are absent, and 

 therefore where the Drift, if ever deposited, has been entirely denuded 

 — the last trace of Drift remaining would be the stones, not the sand 

 or clay. The Chalk is generally covered with a thin clayej'^ or loamy 

 soil, and sometimes with a thicker deposit of unworn flints in a 

 claj- ey matrix, known as the " clay with flints." These deposits 

 have been generally explained by the dissolving action of rain water 

 on the Chalk, which in time leaves a non-calcareous soil formed from 

 the insoluble residue. Probably to a large extent this is correct, 

 though the insoluble residue ought generally to consist of a much 

 larger proportion of flint and less clay than is found. It is this 

 excess of clay, and also the clay soils on sandy land, which I now 

 attempt to explain. 



Chemical analyses of soils from the Chalk Wolds and Downs, 

 though showing a great difierence between the soil and subsoil, leave 

 it still possible that the one may be formed by the weathering of the 

 other. Microscopic examination, however, yields a quite different 

 result. The sand in the soil is at once seen to be quartz, not flint, 

 and therefore it cannot be derived from the Chalk. 



In the Lincolnshire Wolds the origin of this sand is clear, for sand 

 is still occasionally blown up from the low-lying country to the 



