194 THE OLD RED SANDSTONE. 
same principle, its trail of sand and shingle piled up behind 
it. The outlines of the landscape were modified yet further 
by the yielding character of the basement of sandstone or 
shale on which the Plutonic beds so often rest. The base 
ment crumbled away as the tides and waves broke against it. 
The injected beds above, undermined in the process, and with 
a vertical cleavage, induced by their columnar tendency, fell 
down in masses that left a front perpendicular as a wall. 
Each bed came thus to present its own upright line of preci- 
pice ; and hence — when they rise bed above bed, as often 
occurs — the stair-like outline of hill to which the trap rocks 
owe their name; hence the outline of the Dalmahoy Crags, 
for instance, and of the southern and western front of Salis- 
bury Crags. 
In all the sedimentary formations the peculiarities of sce- 
nery depend on three circumstances — on the Plutonic agen- 
cies, the denuding agencies, and the manner and proportions 
in which the harder and softer beds of the deposits on which 
these operated alternate with one another. There is an union 
of the active and the passive in the formation of landscape ; 
that which disturbs and grinds down, and that which, accord- 
ing to its texture and composition, affects, if | may so speak, 
a peculiar style of being ground down and disturbed ; and it 
is in the passive circumstances that the peculiarities chiefly 
originate. Hence it is that the scenery of the Chalk differs 
from the scenery of the Oolite, and both from that of the 
Coal Measures. The Old Red Sandstone has also its pecu- 
liarities of prospect, which vary according to its formations, 
and the amount and character of the disturbing and denuding 
agencies to which these have been exposed. Instead, how- 
ever, of crowding its varicus, and, in some instances, diszim- 
ilar features into one landscape, I shall introduce to the reader 
