We do not select the rocks which form the title of this chapter from mere arbitrary choice, or because they are geographically connected with the district under review, but because they are immediately the next in the chronological order of our course. The Sidlaws and Ochils have their position as precisely determined in relation to time as to space, for difficult often as it may be to fix the sequence of events within the historical era, there is generally no lack of evidence by which to ascertain, in the far remoter times, _when_ the several strata and the igneous masses assumed their respective places on the surface of the globe. The proofs here are of a cumulative character, and irresistibly conclusive. The animate and inanimate things of earth, the living and the dead, are both admissible witnesses in the question, and their testimony is alike unexceptionable. The saurian seas had been disturbed upon the upheaval of their beds; these with their organic contents were elevated by the irruption of plutonic matter, and in their altered position gave a bolder contour and additional bulk to the primitive land. New accumulations were forming during the devonian period in the waters still mightily agitated along the lines of disturbance; new races of scale-enameled creatures occupied their depths, and huge crustaceans anchored among their rocky shallows. The interior regions again let loose their giant forces, and these chains of hills rose above the surface, disrupting and heaving into day the various deposits of the old red sandstone. Hence the formation of the one set of rocks preceded, in the order of time, the elevation of the other: not an islet appeared over all these parts while the sedimentary strata were accumulating beneath: plants and trees covered the flanks of the Grampians, algæ and fuci abounded in the waters, and myriads of fishes sported amid their luxuriance; but as yet there was no basin of the Tay, no fertile Carse of Gowrie, no kingdom of Fife stored to repletion with its precious metals of iron, lime, and coal. The Sidlaws and Ochils, therefore, become invested with even a romantic interest, when we thus view them in their geological relations—their age precisely defined—and themselves, flinty and weather-stained, the memorials of the vast convulsions and changes of nature. They mark the outgoing of a period comparatively barren of vegetable life, and the incoming of the exuberant products of the carboniferous epoch.