TRANSACTIONS OF THE SECTIONS. 57 
is now bare in consequence of the removal from above it* of a thickness of 
many hundred feet of Chalk, and of other beds below the Chalk. But this reason- 
ing may be carried out with respect to the whole of the flat lands of England and 
the British Islands. The great central plain of Ireland, for instance, stretching from 
Dublin Bay to Galway Bay, with an average elevation of less than 300 feet above 
the sea, has immediately beneath it abruptly undulating beds of Carboniferous 
limestone, rising up at all angles, and dipping in all directions. The most level 
arts of the surface sometimes cut horizontally across the most contorted and highly 
inclined beds. The small isolated hills scattered here and there about the plain 
are formed sometimes of beds of Old Red Sandstone that rise up from honest the 
bottom of the Limestone, and sometimes of beds of Coal-measures which rest upon 
the top of it. It is here abundantly evident, then, that the internal forces of dis- 
turbance which have bent the beds from their original horizontality into so many 
euryes, and broken them by so many dislocations, had nothing at all to do with 
the production of the present surface, which has been formed across all these bent 
and ftoken beds after the disturbances had ceased. 
But, in fact, the very first glance at a geological map of a flat country, if there 
be two or more colours on it representing conformable groups of stratified rocks, is 
= as good a proof of this vast denudation as the most elaborate reasoning. The 
ast-deposited group of beds would of course conceal all those beneath it; itwould be 
represented by one uniform colour. Let the internal forces bend, or tilt, or break it 
in any fashion you like, they cannot of themselves remove a particle of it. It will 
still lie over all those on which it was originally deposited, and the map would show 
the one colour only, unless we go the length of supposing that a piece of the crust 
of the earth could be tossed over like a pancake, and laid down again with its bot- 
tom upwards. 
Ihave taken the case of a plain in the first instance, because it is obvious that 
if we arrive at the conclusion that many plains are low and level because moun- 
tainous masses of rock have been removed from above their present surface, it will 
be easy for us to recognize the proofs of denudation in the hills and mountains, on 
whose flanks the obvious marks of it are still left. 
A little reflection will show us that the outcrop of a bed is always a proof of 
denudation, for the present surface cannot possibly tie the original termination, not 
only of that particular bed, but of all the beds above it. When then a succession 
of beds crop out rapidly one after another, as they always do in all hill-ranges and 
mountain-chains, we cannot escape from the conclusion that the existing surface 
has been formed by the removal of the former extension of the beds. This is the 
inevitable conclusion, whether the surface be horizontal and the beds below it in- 
clined, or the beds be horizontal and the surface inclined, or the surface slope one 
way and the beds dip another, or there be any kind of discordance between the 
“lie” of the beds and the form of the surface of the ground. The only possible 
escape from this conclusion would be in the case where a succession of beds had 
been deposited on a slope, and had never been covered by any other deposit. This, 
however, is a case that could only occur in very recently formed rocks, and cannot 
apply to the outcrop of beds on the flanks of hills or mountains, where the surface 
of the ground itself has a high inclination. 
In such situations the only escape from the conclusion that the surface was formed 
by denudation would be, proof that the undulations of the surface were exactly fol- 
lowed by the undulation of the beds below it, and, in fact, that the very same bed 
was everywhere found to be the one immediately below the surface. 
If we except Volcanos or “ Mountains of Ejection,” all other hills and mountains 
are either caused by the removal of the rocks which once surrounded them, or haye 
suffered from the removal of those that once spread over them. The first kind of 
hills have simply been left high, while the surrounding ground has been worn down 
to a low level about them. In the second kind, the rocks composing them haye, 
indeed, been thrust up from beneath by internal force to a much greater elevation 
than those same rocks have in the surrounding area, and their height is due entirely 
* In this general statement the few feet of peat, or the little banks of drift gravel and 
sand which have been subsequently deposited on or grown over the plain, are, of course, 
disregarded. 
