XXIX.—On the Chronology of the Trap-Rocks of Scotland

Abstract

In the Geology of Scotland, no feature comes at once more prominently before the observer than the number and variety of the trap-rocks. From the Sheant Isles to the Cheviot Hills the map is dotted over with trappean patches, which occur sometimes as long, narrow dykes, and often as irregular sheets, that extend almost over entire counties. The appearance of the rocks on the face of the country is scarcely less marked than on the map, and to their ever-changing varieties, we owe not a little of the characteristic scenery of Scotland. Throughout the wilds of the Inner Hebrides it is the trap-rocks which form many of the precipitous cliff-lines, and the craggy irregular hills. The soft pastoral valleys of the Ochils and the Pentlands lie among trappean rocks, while the hill-ranges, which break up the great central valley of Scotland, more especially the abrupt solitary crags that form such prominent landmarks, owe their existence to the permanence of the trap-rocks of which they consist. In short, there is no group of rocks more constantly found throughout the length and breadth of the island, and none, therefore, which so frequently obtrudes on the geologist or more imperatively demands his attention.