198 THE OLD RED SANDSTONE. 
less bold and ruzged, and affects often long horizontal lines, 
that stretch away without rise or depression, amid the surround- 
ing inequalities of the landscape for miles and leagues, and 
that decline to either side, like roofs of what the architect 
would term a low pitch. The ridge of the Leys in the east- 
ern opening of the Caledonian Valley, so rectilinear in its 
outline, and so sloping in its sides, presents a good illustration 
of this peculiarity. The rectilinear ridge which runs from 
the Southern Sutor of Cromarty far into. the interior of the 
country, and which has been compared in a former chapter 
to the shaft of a spear, furnishes another illustration equally 
apt.* Where the sloping sides of these roof-like ridges 
decline, as in the latter instance, towards an exposed sea- 
coast, we find the slope terminating often in an abrupt line of 
rock dug out by the waves. It is thus a roof set on walls, 
and furnished with eaves. A ditch just finished by the labor- 
er presents regularly sloping sides; but the little stream that 
comes running through gradually widens its bed by digging 
furrows into the slopes, the undermined masses fall in and are 
swept away, and, in the course of a few months, the sides are 
no longer sloping, but abrupt. And such, on a great scale, 
* The valleys which separate these ridges form often spacious friths 
and bays, the frequent occurrence of which in the Old Red Sandstone 
constitutes, in some localities, one of the characteristics of the system. 
Mark in a map of the north of Scotland, how closely friths and estu- 
aries lie crowded together between the counties of Sutherland and In- 
verness. In a line of coast little more than forty miles in extent, 
there occur four arms of the sea—the Friths of Cromarty, Beauly, 
and Dornoch, and the Bay of Munlochy. The Frith of Tay and the 
Basin of Montrose are also semi-marine valleys of the Old Red Sand- 
stone. Two of the finest harbors in Britain, or the world, belong to it 
— Milford Haven, in South Wales, and the Bay of Cromarty. 
