THE OLD RED SANDSTONE. 139 
clay, that dissolve into unctuous masses where washed by 
the sea. In England, the formation consists, throughout its 
entire depth, of beds of red and green marl, with alternating 
beds of the nodular limestones, to which it owes its name, 
and with here and there an interposing band of indurated 
sandstone. 
The Cornstone formation is more extensively developed in 
Forfarshire than in any other district in Scotland; and from 
this circumstance the result of the writer’s observations re- 
garding it, during the course of a recent visit, may be of 
some little interest to the reader. About two thirds the en- 
tire area of this county is composed of Old Red Sandstone. 
It forms a portion of that great belt of the system which, ex- 
tending across the island from the German Ocean to the Frith 
of Clyde, represents the southern bar of the huge sandstone 
frame in which the Highlands of Scotland is set. The Gram- 
pians run along its inner edge —composing part of the pri- 
mary nucleus which the frame encloses: the Sidlaw Hills 
run through its centre in a line nearly parallel to these, and 
separated from them by Strathmore, the great valley of An- 
gus. The valley and the hills thus form, if I may so express 
myself, the mouldings of the frame — mouldings somewhat 
resembling the semi-recta of the architect. There is first, 
reckoning from the mountains downwards, an immense con- 
cave curve — the valley; then an immense convex one — the 
hills; and then a half curve bounded by the sea. The illus- 
tration may further serve to show the present condition of the 
formation: it is a frame much worn by denudation, and — 
just as in a bona fide frame — it is the higher mouldings that 
have suffered most. Layer after layer has been worn down 
on the ridges, exactly as on a raised moulding we may see 
the gold leaf, the red pigment, and the whiting, all ground 
14* 
