96 THE OLD RED SANDSTONE. 
ruptions, there is an inclined wall of rock, which rises at a 
steep angle in the interior to nearly two thousand feet over 
the level of the Great Canal, and overhangs the sea towards 
its northern termination, in precipices of more than a hun- 
dred yards.* 
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 up- 
heaving 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 ex- 
tended athwart the country from south-west to north-east. 
Mark in a map of the island —all the better if it be a geo- 
logical 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 parallei 
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 
* The valley of the Jordan, from the village of Laish to the south- 
ern extremity of the Dead Sea, furnishes another very remarkable 
instance of a geographical right line. 
