408 THE GEOLOGY OF 



displayed, and stretch westwards by the Kilpatrick Hills to the Clyde at 

 Bowling. On the south side of the estuary, they are traceable from Bishop- 

 ton to the hills behind Gourock, thence they extend southeastwards for a 

 distance of thirty miles to Strathavon, where they form a gentle anticlinal 

 fold between the Carboniferous basins of Lanarkshire and Ayrshire. On 

 the east side of the Firth of Clyde they stretch from Gourock by Largs to 

 Ardrossan, they appear in Bute and the Cumbraes, they underlie the Hurlet 

 limestone at Corrie in Arran, and they are well developed to the southwest 

 of Campbeltown, where they rest directly on the sandstones and cornstones 

 of the Upper Old Red Sandstone. Sir A. Geikie has called attention to the 

 thickening and thinning of the lavas in different directions, which has been 

 proved by the detailed mapping of the Geological Survey. For while the 

 plateau-eruptions reach a thickness of 3000 feet in the Kilpatrick Hills they 

 gradually thin away eastwards and disappear east of Stirling. 



Though in the neighbourhood of the Campsie and Kilpatrick Hills, and 

 again between Greenock and Ardrossan, the Lower Carboniferous volcanic 

 rocks rest on the Cement-stone series, yet where the volcanoes remained 

 active for a long course of time this subdivision is sparingly developed. 

 Occasionally there are intercalations of sedimentry material, as, for instance, 

 near Eaglesham, where Professor James Geikie mapped sandstones, shales, 

 clay-ironstones, and impure limestones with Productus giganteus, which are 

 intercalated in tuffs. Plant-remains are frequently entombed in the tuffs, 

 as, for instance, on the east coast of Arran a locality discovered by the late 

 Mr. Wu'nsch and they sometimes form thin seams of coal in the volcanic 

 series, as near Bowling, described by the late Dr. John Young. 



Near the top of the volcanic series there is a gradual passage through 

 fine tuffs, which contain much sedimentarv material, into the basement beds 



-.y*.. 



of the Carboniferous Limestone series. This passage has been traced round 

 the north portion of the Ayrshire field near Kilbirnie, and from Beith to 

 Stewarton ; again near Eaglesham in Renfrewshire, and at the foot of the 

 Campsie Fells, west of Kilsyth. It is thus obvious that the Lower Carboni- 

 ferous volcanoes, in certain poitions of the Clyde area, must have remained 

 active during the greater part of the Calciferous Sandstone period. Such 

 prolonged volcanic activity accounts in great measure for the absence in the 

 West of Scotland of the upper or oil-shale group of the Calciferous Sandstone 

 series met with in the basin of the Forth. The latter possesses different 

 lithological characters from those of the Cement-stone group, for they consist 

 of oil-shales, blue and black shales, clay-ironstones, estuarine and marine lime- 

 stones, yellow sandstones, and occasional seams of coal. Recently fine sec- 

 tions of the Cement-stone group have been exposed in artificial openings in the 

 old part of Edinburgh, where they pass underneath the volcanic rocks of 

 Arthur's Seat the equivalents of the Renfrewshire volcanic series these 

 in turn being overlaid by the oil-shale group of the Lothians. The mem- 

 bers of the latter group, so well developed in Midlothian and Linlith- 

 gowshire, are traceable southwestwards as far as Auchengray near the 

 east boundary of Lanarkshire, but their occurrence has not been proved 

 to the west of that locality. 



The triple classification of the Carboniferous Limestones series (see 

 Table, p. 407) is well represented in the Clyde territory. This division forms 

 a belt of variable width surrounding the great Lanarkshire coal-field on 

 the north, west, and south sides. Frequently the strata are faulted against 

 the underlying volcanic series, as along the southern slope of the Campsie 

 Fells. The Hurlet limestone is the lowest limestone of the series, and is one 

 of the most persistent bands. In the Carluke district the lowest group 

 contains from twelve to fifteen beds of limestone, but the two best 

 known seams in it are the Hurlet and the Hosie limestones. The 

 middle group contains several workable coal-seams, of which the Lesma- 



