
SOILS AND SUBSOILS 385 

clay-soils, which are nowadays seldom tilled, but kept in 
grass. 
Calcareous Rocks ——An absolutely pure limestorie would 
be incapable of yielding a soil. All limestones, however, do 
contain insoluble impurities, such as sand and clay, and the 
soils derived from them are thus usually either loams or clays. 
Good examples of such soils are those met with in the Chalk 
districts of England. They are usually reddish or brown in 
colour, and vary in character from stiff, retentive clays to 
calcareous loains. The soil-caps of those regions are 
naturally thickest in the valleys—the tops and steeper 
slopes of the hills showing little or no soil at all. In some 
places, however, the hills are capped with sheets of flint- 
gravel—the flints having been derived from the graduai 
dissolution of the chalk in which they were formerly embedded. 
Limestones all the world over yield similar reddish, yellowish, 
or brownish clays and loams—the colour being due to the 
presence of iron-oxides. The famous Zevra rossa of Southern 
Europe is a well-known example. As most limestones are 
traversed by joints which have been widened by the action 
of acidulated water, much of the insoluble red earth formed 
at the surface is washed by rain, and, in some cases, by 
melting snow, into these open fissures. Limestone regions, 
therefore, especially when relatively high, are apt to showa 
rocky surface, sparingly sprinkled with a thin clay-like or 
loamy soil. 
2 DRiET “SOILs 
Under this head, as already explained, may be grouped 
all soils which do not owe their origin to the direct disin- 
tegration of the bed-rock, but are the modified upper 
portions of glacial, alluvial, and zolian accumulations of 
every kind. The materials of which they are composed 
have been transported for shorter or greater distances. 
Glacial Soils.—These soils are usually somewhat tena- 
ceous clays, but vary considerably in character. They 
overlie accumulations of glacial origin, which may consist 
either of stony or essentially stoneless clays—the latter 
being usually laminated, while the former are commonly 
amorphous. 
2s 

