1852.] NICOL ON THE GEOLOGY OF CANTYRE. 411 



uncommonly of one, two, or even three feet in diameter. In the eon- 

 glomerate forming the precipitous coast to the south of Kildalloig, I 

 measured one boulder, still fixed in the rock, 3^ feet long by about 

 3 feet in breadth and thickness, and several masses of almost equal di- 

 mensions, evidently washed out of the rock, were strewed on the beach 

 around. The mineralogical character of the larger pebbles composing 

 these rocks is singularly uniform in each locality. Of eighteen spe- 

 cimens collected at random from one place in Glenramskill Burn, ten 

 were a hard reddish sandstone, two coarser sandstones, and the re- 

 maining six reddish brown felspar or clay stone porphyries. The con- 

 glomerates on the east coast consist almost entirely of reddish brown 

 porphyries, not unlike those of Davar island in the immediate vicinity. 

 Thus fourteen specimens collected in one spot near Kildalloig were en- 

 tirely of this nature, and only differed in the more or less abundance 

 of light green crystals dispersed through the dark clove-brown basis. 

 In eighteen specimens from another point not far distant, fourteen 

 were also clove-brown porphyries, and four either similar rocks or very 

 hard compact hornstones. In the conglomerates on Knock-Scalbert, 

 north of Campbeltown, the boulders again were chiefly common white 

 quartz, a rock not now seen in situ near this place. In the conglo- 

 merate west of Southend near Keills, quartz, hardened sandstone, and 

 light-greenish porphyritic traps predominated. In all these cases the 

 conglomerates rest on, or are in the immediate vicinity of, the mica- 

 slate, but I have observed no fragments of it or of other so-called 

 primary strata among their materials. This is the more remarkable, 

 as both the size of the boulders and their uniform character in each 

 locality prove that they have not been drifted from a distance, but are 

 the mere water-worn detritus of a shore consisting of similar rocks. 

 Though the laminar texture of the mica-slate renders it very friable, 

 and mica-slate boulders are consequently far from common constituents 

 of conglomerates, yet this alone will not account for their absence from 

 these deposits. Where this rock now forms the shore, masses of it, 

 of all sizes and in various stages of attrition, abound, and must enter 

 largely into the composition of any boulder deposit now forming. In 

 the Boulder Clay or Drift they are also numerous, and are frequently 

 found fifty miles from their native Highlands, resting on the Silurian 

 strata in the south of Scotland. 



The red sandstone connected with these conglomerates, and skirt- 

 ing the east and south coasts of the peninsula, is often a very pecu- 

 liar rock. It is frequently associated with felspar or claystone 

 porphyries, and is then apparently composed in great part of similar 

 felspathous matter. It then either passes into the porphyries by in- 

 sensible gradations, or is so intercalated and mixed up with them that 

 the division-line cannot be determined. A section seen near the 

 south-east coast-road, about two and a half miles from Campbeltown, 

 furnishes a good illustration of these gradations. It exhibits a series 

 of thin beds, from 1 to 2 inches each in thickness, of which the upper 

 beds are decided sandstones, whilst the lower approximate more and 

 more to the porphyries. The higher beds are of a reddish brown or 

 yellow colour, somewhat porous, and consist of numerous thin layers 



