1 2 Journal of Travel and Natural History 



long continued is able to produce, and on the simplicity of the 

 means which nature employs in all her operations, who sees in 

 this nothing but the gradual working of a stream that once flowed 

 as high as the top of the ridge which it now so deeply intersects, 

 and has cut its course through the rock, in the same way, and 

 almost with the same instrument, by which the lapidarj^ divides a 

 block of marble or granite." 



IV. From the surface of the whole country there has been removed 

 a vast amotmt of solid rock, under which the present hills and valleys 

 were once deeply buried. 



In this proposition lies the key to the whole question ; but some 

 little attention is required before its full significance is understood. 

 It will, therefore, be of advantage first to bring forward a few 

 forcible illustrations of its truth, and then to pass on to the infer- 

 ences which necessarily flow from it. 



If the reader will turn back to the long section (fig. i) giving a 

 generalised sketch of the geological structure of Scotland, he will 

 not fail to notice that the curves of the strata there represented are 

 cut off by the surface of the ground. The strata, once approxi- 

 mately horizontal, have been thrown into folds, and a great portion 

 of the upper ends of these folds has been removed. In the case 

 of such a valley as that of Loch Tay, for instance, the dome of 

 arched rock has been worn down into a long and deep hollow, but 

 the upward-pointing edges of the strata on each side of the valley 

 shew how the rocks once extended upward, and how, in imagina- 

 tion, we must prolong them into the air in order to realize the size 

 of the mass that has disappeared. This removal of rock from the 

 surface, and the consequent exposure of portions which once lay 

 buried under overlying masses, is called by geologists the process 

 of denudatioji. Now, the whole surface of the country has largely 

 suftered in this way ; over the whole Highlands the highly inclined 

 or vertical edges of the strata come up along the sides of the glens 

 and mountains. Every such exposed edge is the remnant of a bed 

 which once rose hundreds or thousands of feet above the point to 

 which it has now been worn down : and hence it follows, that from 

 the surface of the Highlands a thickness of hundreds, or rather 

 thousands, of feet of solid rock has been worn away. 



Nor is this lesson of vast waste less impressively taught us by 

 tlie southern uplands of the country. There, too, a series of con- 



