GRAVEL MAY BE TRACED TO ITS NATIVE ROCK. 191 
the history of the formation and extent of those deposits of loam and 
gravel which I have already to a certain degree marked out in tracing 
that of the elephants embedded in them, and which, as I have before 
stated, are of universal occurrence in this as in every other country. 
The loam itself possesses no character by which it is easy to 
ascertain the source from which it has been derived, but usually varies 
with the nature of the hills composing the adjacent districts. It is 
of immense extent on the Continent, is known in Germany by the 
appellation of “ Dammerde,” and of “ Terrain d’attrissement” in 
Franee; and its occasional abundance on the chalk of the north of 
France is the cause of greater fertility in some of the chalky districts 
of that country than of our own. But the deposits of gravel contain 
solid fragments, and often large blocks of granite and other rocks, 
which can be traced to their parent mountain; the position of which 
with respect to the fragments is important, as affording a proof of 
the direction of the currents that drifted them to their present place 
of lodgment. 
This diluvial gravel is almost always of a compound character, 
containing amongst the detritus of each immediate neighbourhood, 
which usually forms its greatest bulk, rolled fragments of rocks, whose 
native bed occurs only at great distances, and which must have been 
drifted thence at the time of the formation of the gravel, in which 
they are at present lodged. 
Now, if we examine with this view the eastern coast of England, 
we shall find that from the mouth of the Tweed to that of the 
Thames, it is covered irregularly with beds of superficial loom, or 
clay and gravel, of enormous thickness, not only in the lowland dis¬ 
tricts, but also on the summits of lofty hills, and on the elevated 
