SOILS AND SUBSOILS 387 
boulders become more and more numerous, while the colour 
and texture of the clay gradually change, as crushed and 
comminuted sandstone enters more and more largely into its 
composition. The majority of the stones and boulders, how- 
ever, are still of Silurian parentage—doubtless due to the 
fact of their superior durability—the red sandstones being 
much more readily pulverised. The till continues to present 
much the same appearance after the region of red sandstone 
has been left behind, but gradually it loses its pronounced 
red colour as Kelso is approached, while fragments of certain 
igneous rocks, which crop to the surface above that town, 
begin to abound. From Kelso to the sea the prevalent rocks 
are brown, reddish, grey, and white sandstones, sandy shales, 
marls, etc. The overlying till, therefore, is a somewhat 
arenaceous clay, light brown as a rule, but here and there 
with a reddish tinge. The bulk of the finer grained materials 
of this till are of local origin, but the most conspicuous stones 
and boulders are still greywacké commingled with abundant 
_ fragments of the “ Kelso trap-rocks,’ and other igneous rocks 
traversed by the old ice-sheet. Similar phenomena are 
encountered everywhere in regions where boulder-clay occurs. 
While it is true, therefore, that this accumulation has a more 
or less local character—and this is especially the case with its 
finer grained materials—yet it must be remembered that the 
till formed in one place tended to travel forward with the ice. 
In this way boulder-clay often came to be deposited upon 
bed-rock of a very different character from that of the region 
where it was actually formed. No small proportion of the 
stones, and even of the gritty and clay-like material of the 
till that covers the low grounds of a country, is often of more 
or less distant derivation. 
It will now be readily understood that the soils yielded 
by boulder-clay are of very unequal character and value. 
The dark lead-coloured tenaceous till met with in many 
Carboniferous tracts gives a most ungrateful soil—a thin, 
cold, unctuous, sticky clay in wet weather; and in drought, 
hard and unyielding. In other places within the same 
geological area, the till has proved more kindly—owing 
chiefly to a larger proportion of comminuted sandstone, 
limestone, and igneous rocks. The red and brown coloured 

