MR. H. 13. WOODWARD ON THE SOILS AND SUBSOILS OF NORFOLK. 403 
the alluvial flats if the rivers overflow their banks. Clay-vales 
locally have their heavy soils ameliorated by downwashes of lighter 
materials from bordering hills, so that on isolated hills and on the 
brows of uplands less soil and a less amount of weathered subsoil 
are to be expected than on plateaus or in vales. 
That subsoils possess infinite variety in structure and composition 
may be gathered from a study of the lithological characters of the 
many geological formations, which include limestone, slate, sand- 
stone, conglomerate and other hard rocks, as well as marl, clay, 
loam, sand, gravel, and other soft and loose materials. Some 
formations are fairly uniform masses of strata of considerable 
thickness, others exhibit great diversity of character within narrow 
limits. All are more or less subject to modification where they 
approach the surface, through the influence of frost and rain : 
harder rocks are broken up, calcareous rocks are partially dissolved 
away, while those which are grey or dark blue at a depth become 
a rusty brown through decomposition of the iron-salts which they 
contain. The depth of the weathered rock beneath the actual 
soil varies considerably in different areas even on formations of 
similar age and character. This is to some extent owing to 
geological changes, but mainly to the nature of the ground. Thus 
chalky Boulder Clay and shelly Crag, which are usually decalcified 
near the surface, are sometimes turned up by deep ploughing in 
situations where but little weathered rock or soil can accumulate. 
In the southern counties of England we find in places greater 
thicknesses of weathered rock than to the north and east, in 
regions where the land in Pleistocene times was overspread by 
a mantle of ice which incorporated the ancient soils and subsoils 
with erratic detritus, and worked up all the debris into the newer 
formations known as Glacial Drifts. These Drifts, which are of 
very mixed composition, have been distributed over much of 
Norfolk, and to them the diversity and natural fertility of the 
soils are principally due. The soils in Norfolk have thus resulted 
from the modification of the surface after the period of great cold, 
and, indeed, after the torrential action which, following the melting 
of the ice, spread out accumulations of boulder gravel, furrowed 
the surface, and marked out the courses of the streams. The later 
erosion, when the area had been subjected to depression, has been 
carried on by frost, rain, and streams, and it has been more directly 
influenced, not only by the physical features, but by the porous or 
