1857.] GEIKIE SKYE. 21 



having never reached the surface, may be the underground prolon- 

 gations of the hills now visible. The minor protrusions of syenite 

 seen in various parts of the metamorphic region seem to favour this 

 supposition*. 



I should leave my notice of the metamorphism of Strath incom- 

 plete were I to omit mention of the fact that, as the basalt-dykes 

 were erupted previous to the syenite, they must have suffered from 

 the general baking of the rocks. The dykes of the altered area are 

 perhaps harder and closer-grained than those among the unaltered 

 strata. But I confess that the great variety in the texture of the 

 basalt-dykes, as a whole, renders it difficult, if not impossible, to esta- 

 blish any distinction among them. 



Faults. — The faults of the district are not very numerous, nor do 

 they merit special remark. Their general strike is northerly, vary- 

 ing a few degrees east or west ; the details of several have been given 

 above, and for the others I must be permitted to refer to the accom- 

 panying map and sections (PL I.). 



Conclusion. — I have thus gone over what seemed most worthy of 

 notice in the geology of Strath, and, in conclusion, will now briefly 

 sum up these scattered facts, that the general bearings of this paper 

 upon Hebridean geology may be distinctly seen. 



The old basement-rock upon which the various changes described 

 took place, is the Red Sandstone of Sleat. As it has never yielded 

 any fossils, its age is still matter of doubt. It can scarcely be 

 Old Red Sandstone ; possibly it is Silurian, or one of the later de- 

 posits of the gneissic series, for it graduates southwards into the 

 schists of the Sleat hills. The geological history of Strath accord- 

 ingly opens among the records of a venerable antiquity. But here a 

 great gap occurs in its chronology. The district contains no me- 

 morials of palaeozoic life ; and thus, while other parts of Scotland had 

 successively their land and sea of the Old Red Sandstone, Carboni- 

 ferous, and Permian periods, the old grey hills of Skye seern to have 

 remained unchanged. 



After the lapse of long centuries, the Red Sandstone, shattered and 

 broken, slowly sank beneath an ocean in which Ammonites, Belemnites, 

 and Gryphcece began to appear. The margin of the foundering land was 

 first fringed with a band of conglomerate as the waves broke against 

 the clifTs, while greenish sand accumulated farther from the shore. 

 In deeper and stiller water the peculiar organisms of the Lias began 

 to abound ; seams of limestone were slowly aggregated, and, at least 

 at one spot, a reef of massive IsastrcEce gleamed white beneath the 

 waves. The growth of these corals was suddenly arrested by the 

 inroad of a large amount of muddy sediment, which silted up around 

 them, and insinuated itself into their minutest crevice. By degrees 

 the waters became clear, organisms began once more to swarm, but 

 the Isastrcea had perished for ever. Beds of limestone, occasionally 

 checked by irruptions of argillaceous matter brought by the shifting 

 currents, were gradually elaborated ; and when they had attained a 



* I find that Macculloch throws out a similar conjecture (Description, vol. i. 

 p. 333). 



