﻿1861.] 



MTJECHISON ASTD GEIKIE HIGHLANDS. 



209 



rock, the equivalent of the upper quartz-rock of the North, which is 

 overlain in both localities by an upper group of schists. 



The lowest limestone is seen to the north-east of Islay House, 

 whence it runs for some miles towards the north-east in a broad 

 band. It is a grey crystalline rock, sometimes well bedded, and 

 exactly resembles portions of the Assynt rock. We could detect in 

 it no trace of fossils. 



The space between this and the next limestone is probably occu- 

 pied for the most part by soft schists, as the country is low and 

 covered with peat. The second limestone resembles .the first, but 

 appears to be of smaller dimensions. 



After another interspace of moor, with here and there exposures 

 of schistose strata dipping towards the south-east, we encounter the 

 third limestone, which follows the curving outline of the escarpment 

 of quartz-rock and plunges sharply below it. This limestone, owing 

 to the form of the island, can be traced further than the others. It 

 extends from Lossit, near the shore of the Sound of Islay, to the 

 Mull of Oe, a distance of 16 or 18 miles. The cliff line at the latter 

 locality affords a good section of the junction of this calcareous seam 

 with the schists below and the strata of quartz-rock above it. 



In tracing it northward along the western slopes of the mountains, 

 we find that it has a regular course until within a few yards of the 

 shore of the Sound of Islay near Lossit, where it suddenly wheels 

 round and passes towards the west. By this means it avoids enter- 

 ing the opposite island of Jura, and the superjacent quartz-rock is 

 thus thrown westward along the Islay shores instead of crossing at 

 once with a north-east strike into Jura. 



The district between Lossit and Islay House presents a confused, 

 contorted arrangement of the rocks. The various limestones are no 

 longer separable ; they seem indeed to become blended more or less 

 into one, and on crossing the central valley towards the north they 

 die out altogether, so that the lower grauwacke-grits and the upper 

 quartz-rock unite. They are considerably mineralized, containing, 

 in at least one locality, veins of lead which are worked. 



The upper limestone is surmounted by some schistose strata, well 

 seen at the Mull of Oe, which graduate upward into white quartz- 

 rock. The great mountain-masses of Beinn Bhan, Ben Vicker, and 

 other summits, looking in the distance as if capped with snow, consist 

 entirely of beds of this quartz-rock, having a south-easterly dip at 

 from 30° to 40°. Sometimes, however, the rock has a reddish hue 

 and a coarse granular texture, as along the cliff line of Macarthur's 

 Head, where the strata have been considerably broken. Further to 

 the north it even assumes the character of a breccia, the included 

 fragments consisting of variously coloured felspathic rocks. The 

 upper beds of this quartzose mass descend rapidly towards the east, 

 and are succeeded by a group of schists (with intruded beds of 

 greenstone), which, in alternate ridge and valley, occupies the de- 

 scending ground between the grey mountain-chain and the eastern 

 shore*. 



* Macculloch (Trans. Geol. Soc. vol. ii. p. 413) says, "Extensive and correct 



