DURING THE TERTIARY PERIOD IN THE BRITISH ISLES. 169 



down into Strath na Creitheach, whence it sweeps northward between the red cone of 

 Ruadh Stac and the black rugged declivities of Garbh Beinn. On Meall Dearg the 

 granophyre becomes fine-grained and even felsitic in texture, and sends into the 

 contiguous gabbro abundant veins, some of which show fine flow-structure. There is no 

 more singular scene in Skye than the lonely tract on the south side of this hill. The 

 ground for some way is nearly level, and strewn with red shingle from the decomposing 

 granophyre underneath. It reminds one of some parts of the desert " Bad lands " of 

 Western America. Grim dark crags of gabbro, streaked with red veins from the 

 granophyre, rise along its western border beyond which tower the black precipices of the 

 Cuillins, while the flaming reddish-yellow cones of Glen Sligachan stand out against the 

 northern sky. The gabbro here includes much fine-grained, sometimes amygdaloidal rock, 

 belonging probably to the plateau-basalts, and sends veins through it, but the veins 

 from the granophyre-mass cross these. An alteration of the basic rocks like that already 

 described may be noticed here. Next the granophyre, they are dull, compact, splintery, 

 shattery, and much veined, and weather with a white crust. 



(4) Relation to the Basic Dykes and Veins. — In my early paper on the Geology of 

 Strath I pointed out that the " syenite " bosses of Skye cut off most of the basalt-dykes, 

 but are themselves traversed by a few others.* Though I have since been able to 

 confirm and extend this observation, the locality that furnished my original evidence 

 affords in small compass a clearer presentation of the facts than I have elsewhere met 

 with. I then referred to the sections visible at the eastern end of the boss of Beinn an 

 Dubhaich ; but similar and even better ones may be cited from the whole northern 

 and southern margins of that eruptive rock. On the north side an extraordinary 

 number of dykes may be traced in the limestone from the shores of Loch Slapin east- 

 wards. They have a general north-westerly trend, but one after another, as I have 

 already remarked, they are abruptly cut off by the granophyre. The latter rock is 

 exposed for nearly a mile in almost continuous section along the shore of Loch Slapin. 

 Yet though I was on the outlook for dykes in it, I found only one. Immediately 

 beyond the eruptive boss, however, they at once appear on either side up to the very 

 edge of the granophyre, where they abruptly cease. The conclusion cannot be resisted 

 that the protrusion of the acid rock took place after most of the dykes of the district 

 had been formed, but before the emission of the very latest dykes which pursue a north- 

 west course across the boss (fig. 54). 



Some sections on the southern margin of Beinn an Dubbaich complete the demon- 

 stration that such has been the order of appearance of the rocks. Near the head of 

 the Allt Leth Slighe (or Half-way Burn), where the granophyre sends a long tongue 

 into the limestone, a N.W. basalt dyke is abruptly cut off by the main body of the 

 boss and by the protruded vein (fig. 56). Besides this truncation, the acid rock protrudes 

 strings and threads of its own substance into and across the dyke, these injected portions 

 being as usual of an exceedingly fine felsitic texture. 



* Quart. Jour. Geol. Soc, xiv. p. 16. 



