If we except some small patches of Millstone Grit to the E of Barrhead and near Pollokshields, and the limited development of the true Coal-measures on the border of the county of Rutherglen, the whole of the area lying to the roof the volcanic rocks belongs to the Carboniferous Limestone series. The strata are traversed by numerous faults which repeat the valuable seams of coal and ironstone. In the neighbourhood of Johnstone and Linwood they are arranged generally in the form of a synclinal fold. Along the W margin of this basin, near Bridge of Weir, we find the Hurlet Coal and Limestone dipping to the E and SE being rapidly followed by the Lillies Oil Shale, the Hosie Limestone, and the Johnstone Clayband Ironstone. In the neighbourhood of Linwood the deepest part of the basin is reached, the Lower Garscadden Clayband Ironstone being succeeded by various coal seams belonging to the middle coal-bearing group. To the S of Johnstone there is a remarkable development of intrusive sheets of basalt occurring near the base of the Carboniferous Limestone series. The largest of these masses occurs in the neighbourhood of Quarrelton, measuring 1 1/2 mile from N to S, and consisting of dolerite. It is underlaid by the thick Quarrelton Coal, which rests on a basement of volcanic tuff reposing on white sandstones intervening between the Quarrelton Coal and the volcanic rocks of the Cementstone group. Near Howwood, the intrusive sheet just referred to, and the associated strata, form an anticlinal arch, from which the Hurlet Coal and Limestone dip away towards the E and W. Similar intrusive sheets of basalt rock occur about 1 mile to the NE of Paisley, where they occupy a similar geological horizon.
     Passing E to that portion of the basin extending from Hurlet to Shawlands and Crossmyloof, there is a splendid development of the middle coal-bearing and upper limestone groups. A traverse from Hurlet E to Cowglen shows, if we exclude minor faults, a general ascending section from the outcrop of the Hurlet Coal and Limestone, through the Lillies Oil Shale, Hosie Limestone, and the various ironstones and coals of the middle coalbearing group, to the Cowglen Limestone. The latter bed forms the base of the upper limestone group, thus occupying a similar position with the Index Limestone in the Lanarkshire basin. The valuable coals and ironstones of the middle group also occur to the N of Shawlands and Crossmyloof, where they are abruptly truncated by a fault throwing down to the NE the Millstone Grit and the Coal-measures. Near Crossmyloof the coal seams of the middle group of the Carboniferous Limestone series are actually brought into conjunction with the numerous coals and ironstones of the true Coal-measures.
     Advancing S from Crossmyloof, where the coal seams of the middle group have a general dip to the S, there is a general ascending series through the upper limestone group to the overlying Millstone Grit. The observer crosses in succession the Cowglen or Index Limestone, the white Giffnock sandstones, the Orchard Limestone, which is underlaid by a thin seam of coal; while at the top he finds the Arden Limestone, also underlaid by a seam of coal. In this district the Arden Limestone is regarded as marking the boundary between the Carboniferous Limestone series and the overlying Millstone Grit. The limestones of the upper group are by no means very fossiliferous, but there is a bed of shale at Orchard teeming with fossils which has become famous among the geologists of the west of Scotland. From this band alone Messrs. Young and Armstrong have chronicled upwards of 120 species of univalve and bivalve shells, together with Foraminifera and Entomostraca.
     To the E of Barrhead there is a small outlier of thick yellow sandstones, representing the Millstone Grit, resting on the Arden Limestone which rises from underneath the sandstones on every side save the E, where the basin is truncated by a NE and SW fault. Another little outlier of Millstone Grit resting on the Arden Limestone occurs about a mile to the SE of Thornliebank.
     Throughout the county there are numerous basalt dykes of Tertiary age, piercing alike the Lower Carboniferous volcanic rocks and the Carboniferous Limestone series. Perhaps the best examples occur in the volcanic area to the NW of Lochwinnoch, where some of the dykes run parallel with each other for a distance of several miles.