﻿1851.] MURCHISON — SILURIAN ROCKS OF SCOTLAND. 



153 



upwards of twenty varieties of rock among the pebbles, varying in 

 dimensions from the size of musket bullets to two and three feet 

 diameter. Among them are small specimens of earthy greywacke and 

 larger ones of hard siliceous greywacke, Lydian stone, hornstone of 

 various colours passing to porphyry, dark red jasper, red jaspidified 

 felspar-rock, broken and re-cemented in the pudding-stone, granites 

 both of red hornblendic and grey syenitic varieties, and also the pro- 

 togine variety of that rock, grey porphyry with long acicular crystals 

 of felspar, brown and red felspar-porphyry, occasionally with highly 

 polished surfaces, porphyritic felspar-rock or Corneen, greenstone, 

 both common and porphyritic, &c. All these varied materials, none 

 of which are like the old crystalline rocks of the Highlands, whilst 

 some were even undistinguishable from igneous rocks which we know 

 to be of posterior eruption to these very conglomerates, are cemented 

 in a matrix of quartz and dark brownish clay (decomposed greywacke) 

 with some scales of mica, fragments of hornblende, and occasional 

 veins of fibrous calc-spar. 



The conglomerate in this locality is several hundred feet thick, 

 and, mounting up in sloping terraces on the shoulders of the trap- 

 rocks, ranges, with some courses of intercalated sandstone, into the 

 interior. Such conglomerates are also met with at various places 

 inland ; for we traversed one band in passing to Barr, a few miles 

 distant from the coast. Seeing that various courses of conglomerate 

 are subordinate to the shelly sandstones, and believing that the 

 group supports the orthoceratite and graptolite schists which have 

 been described, J cannot divest myself of the opinion, that the 

 uppermost of these conglomerates (of which I believe there are 

 several courses at various horizons in the sandstone of this region) 

 is not far removed from the upper limit of the Lower Silurian rocks 

 of Scotland. The analogy of the English Silurian rocks favours this 

 view ; for in them the pebbly conglomerates which are of most im- 

 portance occur in certain districts, as at Presteign near Welshpool, 

 towards the upper limits of the Lower Silurian. As in the Welsh 

 examples, the most powerful of these Scottish Silurian conglomerates, 

 or that of Kennedy's Pass, though on a much grander scale, is also 

 but of local development, and the Bohemian section is also analogous : 

 I shall, indeed, give a transverse section of all the Silurian strata in 

 the heart of the South of Scotland, from the N. of Dumfriesshire to 

 Balmae Head in Kircudbright, which exhibits no trace of such a rock. 



Limestones and Schists (with Trap Rocks). — Let us now con- 

 sider the character and relations of the limestones which appear at 

 intervals in the more southern tract watered by the Stinchar River 

 and its tributary the Assell. A very large portion of the coast from 

 the conglomerate of Kennedy's Pass to Ballantrae is occupied by 

 eruptive rocks, consisting of greenstone and porphyry, with much 

 diallage rock and serpentine, some purple and spotted varieties of 

 which reminded me of the serpentines of Coverack Cove in Corn- 

 wall. Metamorphic schists are also abundant. Occupying Bennan 

 Head and extending to some distance inland, the intrusive rocks 

 usurp, however, most of the surface, and separate the limestones of 



VOL. VII. PART I. M 



