DURING THE TERTIARY PERIOD IN THE BRITISH ISLES. 



97 



outcrop of the nearly flat basalt-beds, rise from the bottoms of the valleys into flat-topped 

 ridges and truncated cones (fig. 21). The hills everywhere present a curiously tabular 

 form that bears witness to the horizontal sheets of rock of which they are composed* 

 And along the stupendous sea-precipices, each successive sheet of basalt can be counted 

 from base to summit, and followed from promontory to promontory (fig. 22). In the 

 district of Trotternish, the basalt hills reach a height of 2360 feet. Further west, the 

 singular flat-topped eminences, called "Macleod's Tables" (fig. 21), ascend to 1600 

 feet. 



Along the western side of Skye, the basalts descend beneath the level of the Atlantic. 

 Along the eastern side their base runs on the top of the great Jurassic escarpment, whose 

 white and yellow sandstones form there, and on the east side of Eaasay, so prominent a 

 feature in the landscape. To the south-east, the regularity of the volcanic plateau is 

 effaced, as in Mull and Ardnamurchan, by the protrusion of the extensive mass of eruptive 

 rocks constituting the Cuillin and Red Hills, east of which the basalts have been almost 





Fig. 22.— "Macleod's Maidens " and part of Basalt Cliffs of Skye. 



entirely removed by denudation, so as to expose the older rocks which they once covered, 

 and through which the later eruptive bosses made their way. This is undoubtedly the 

 most instructive district for the study of that later phase in the volcanic history of 

 Britain comprised in the eruptive bosses of basic and acid rocks. 



The magnificent plateau of this island has been so profoundly cut down into glens 

 and arms of the sea, and its component layers are exposed along so many leagues of 

 noble precipice, that its structure is perhaps more completely laid open than that of any 

 of the other areas. It is built up of a succession of basalts and dolerites of the usual 

 types, which probably reach a thickness of more than 2000 feet, though in their instance, 

 also, denudation has left only a portion of them, without any evidence by which to reckon 

 what their total original depth may have been. In rambling over Skye, the geologist is 

 more than ever struck with the remarkable scarcity and insignificance of the interstrati- 

 fications of tuff or of any other kind of sedimentary deposit between the successive lava- 



* These features are more fully described in my Scenery of Scotland, 2d edit. (1887), pp. 74, 145, 216. 



