200 Mr. Bryce on the Geology of the Island of Bute. 



between contiguous and dissimilar strata. The line of junction seems to 

 run fetal! the middle of the valley, but it is usually wholly concealed; 

 now by marshy ground, and again by deep accumulations of shingle and 

 other rolled and transported materials. On opposite sides, however, the 

 rocks are perfectly distinct. The northern portion between the Kyles on 

 one side, and Kaimes and Ettrick bays on the other, is composed of 

 mica slate. The district south of this, and which has the valley behind 

 Rothesay for its southern boundary, is composed of siliceous and common 

 clay slate. The portion reaching from this valley to that of Kilchattan, 

 is occupied by a coarse sandstone, usually conglomerate ; and, finally, tho 

 southern portion is composed of various rocks of the trap family, which 

 have been erupted through the sandstone, and overlie it in a nearly 

 conformable position. The connexion of these strata with the mainland 

 is most intimate. The slate and sandstone are, in fact, the terminal 

 portions of those great bands of sedimentary strata which stretch from 

 Angus to the Clyde, being parallel throughout to the granitic axis of the 

 Grampian chain : while the erupted rocks in the south of the island are 

 a prolongation of the great outburst of the igneous formations, which, 

 affecting a general parallelism with the same axis, extends from sea to 

 sea in considerable ranges, as the Kilpatrick and Campsie hills, the 

 Ochills, and some minor ridges in the south-east of Perthshire. The valleys 

 intersecting the island seem obviously a part of that great system of 

 parallel fractures, which run in a north-east and south-west direction on 

 both sides of the Grampians, and are probably due partly to the original 

 upheaval of that chain, and partly to the subsequent eruption of the 

 igneous rocks just mentioned through the old red sandstone, and the coal 

 formation which rests upon it. 



4. The strata of sandstone are fully exposed on the shore, and in the 

 inland cliffs from Rothesay to Ascog. A little to the south of Bogany 

 Point, limestone appears interstratified with the sandstone, the two rocks 

 gradually passing into one another at the junction. Dr. MacCulloch 

 describes one bed — I noticed several others; but the beds being thin, of 

 small horizontal extent, and containing generally much siliceous matter, 

 the rock is of no great economical importance in this place. On the 

 north side of the small rocky promontory, south of Ascog mill, the lime- 

 stone assumes the nodular structure, and several thin courses of it are 

 seen to traverse beds of a crumbling, brown-coloured shale, subordinate 

 to the sandstone. This shale is of considerable thickness, and appears 

 in the banks above the road. 



The south side of the promontory presents the following section, 

 (No. 3.) The lower bed, a, is a fine-grained bluish-grey nodular limestone, 

 often intermixed with, and undistinguishable from, the adjoining sand- 

 stone. This is succeeded by black, slightly bituminous shale, containing 

 a few very thin veins of coal, less than a quarter of an inch thick. A 

 bed of concretionary limestone, c, rests on the shale, tho base or paste 

 being an impure dark-coloured limestone, and the concretions rounded 



