The direction of this rampart and fosse--this Roman wall of Scottish geological history--seems to have been that in which the volcanic agencies chiefly operated in upheaving the entire island from the abyss. The line survives as a sort of foot-track, hollowed by the frequent tread of earthquakes, to mark the course in which they journeyed. Like one of the great lines in a trigonometrical survey, it enables us, too, to describe the lesser lines, and to determine their average bearing. _The volcanic agencies must have extended athwart the country from south-west to north-east._ Mark in a map of the island--all the better if it be a geological one--the line in which most of our mountain ranges stretch across from the German Ocean to the Atlantic,--the line, too, in which our friths, lochs, and bays, on both the eastern and western coasts, and especially those of the latter, run into the interior. Mark, also, the line of the geological formations, where least broken by insulated groups of hills--the line, for instance, of the Old Red Sandstone belt, which flanks the southern base of the Grampians--the nearly parallel line of our Scottish Coal-field, in its course from sea to sea--the line of the Grauwacke, which forms so large a portion of the south of Scotland--the line of the English Coal-field, of the Lias, of the Oolite, of the Chalk--and how in 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 tertiary depositions. In all these lines, whether of mountains, lakes, friths, or formations, there is an approximation to parallelism 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 immensely 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 Lisbon, during the great earthquake of 1755; and that the impulse, true to its ancient direction, sent the waves in huge furrows to the north-east and the south-west.