﻿1861.] 



JIURCHISON AND GEIKIE HIGHLANDS. 



211 



persistence. These dykes may be seen high on the sides of the grey 

 quartz mountains, and one is especially observable a little below the 

 summit of Ben Vicker. 



The Island of Jura, the magnificent mountain-ranges of which 

 form the deer-forest of our hospitable friend the Laird of Jura, 

 presents no feature which has not been already noticed in the 

 description of Islay. The limestones and lower schistose series are, 

 however, wanting; and the quartz-rock attains a much grander 

 development than in Islay, rising into the Paps of Jura, 2569 feet 

 above the sea. Macculloch has well described the singular and 

 striking view from the summits of these mountains, which altogether 

 constitute the grandest display of quartz-rock to be seen in Scot- 

 land*. Nothing can exceed the distinctness with which the lines 

 of bedding are impressed on the cliffs and along the ridges. The 

 whole island seems spread out as in a map, and we can follow 

 almost the line of each stratum as it winds over hill and crag, 

 valley and tarn, among solitudes that are haunted only by the red- 

 deer and the eagle. Here and there among the grey cliffs we detect 

 the dark line of a basalt-dyke pursuing the even tenor of its way to- 

 wards the north-west, alike over precipitous mountain and deep glen. 



The line of schists which fringe the eastern coast of the island 

 correspond to those that occupy the same part of Islay. They are 

 marked too by the same bines of greenstone, ranging into the beds, 

 and are traversed by the same series of later basalt-dykes. 



Prolongation of the Islay and Jura Rocks up the Linnhe Loch. — 

 The limestones of Islay, overlain, as we have shown, by a great 

 quartz-rock series, are prolonged towards the north-east in the Gar- 

 velloch Isles and the Islands of Lismore and Shuna. The quartz- 

 rock above them, after traversing the length of Jura and Scarba, 

 becomes lost beneath the sea. But we find traces of it again, though 

 in a greatly diminished form, along the eastern shores of the Linnhe 

 Loch, north of Oban. It there occurs as bands of quartz-rock and 

 quartzose flaggy beds among schists, and dips, like the limestones 

 below and the schists above, towards the south-east. The upper 

 schistose series, with its associated limestone bands, skirts the eastern 

 shores of Jura and Scarba, and thence runs towards the north-east, 

 forming, with the addition of later rocks, the chain of islands towards 

 Oban as well as a large part of the mainland. 



The crystalline series of strata, therefore, which is so clearly ex- 

 hibited in Islay, is continued up the Linnhe Loch, the rocks having a 

 steady south-easterly inclination. This line forms one side of the 

 anticlinal arch which has been pointed out as coincident with the 

 direction of the Great Glen, or line of the Caledonian Canal ; the 

 other side is lost beneath the Atlantic. In the reverse or north- 



* Description of Western Islands, vol. ii. p. 205, &c. See also Trans. Geol. Soc. 

 vol. ii., where he gives other details. His section of the order of superposition 

 agrees with our own. He says that the quartz-rock of Jura underlies the slates, 

 and contains water-worn pebbles, also worm-like cylindrical borings, and that it 

 was "originally a stratified sandstone which has been chemically and me- 

 chanically altered." (pp.454, 455, 4G2-3.) 



