THE OLD RED SANDSTONE. 97 
this process of diagonal lining, if I may so speak, the south- 
eastern portion of England comes to be cut off from the 
secondary formations altogether, and, but for the denudation 
of the valley of the Weald, would have exhibited only ter- 
tiary depositions. In all these lines, whether of mountains, 
Jakes, friths, or formations, there is an approximation to par- 
allelism with the line of the great Caledonian valley — proofs 
that the upheaving agency from beneath must have acted in 
this direction from some unknown cause, during all the im- 
measely extended term of its operations, and along the entire 
length of the island. It is a fact not unworthy of remark, 
that the profound depths of Loch Ness undulated in strange 
sympathy with the reeling towers and crashing walls of Lis- 
bon, during the great earthquake of 1755; and that the im- 
pulse, true to its ancient direction, sent the waves in huge 
furrows to the north-east and the south-west. 
The north-eastern portion of this rectilinear wall or chain 
runs, for about thirty miles, through an Old Red Sandstone 
district. ‘The materials which compose it are as unlike those 
of the plain out of which it arises, as the materials of a 
stone dike, running half-way into a field, are unlike the vege- 
table mould which forms the field’s surface. The ridge 
itself is of a granitic texture—a true gneiss. At its base 
we find only conglomerates, sandstones, shales, and stratified 
clays, and these lying against it in very high angles. Hence 
the geological interest of this lower portion of the wall. As 
has been shrewdly remarked by Mr. Murchison,* in one of 
his earlier papers, the gneiss seems to have been forced 
through the sandstone from beneath, in a solid, not a fluid 
form; and as the ridge a-top is a narrow one, and the sides 
* See Transactions of the London Geological Society for 1828 p. 354. 
10* 
