15 



In the island of Arran, the northern portion of which might be 

 expected, from its peculiar structure, to be favourable to the growth 

 and seaward extension of glaciers if such ever existed in Scotland 

 we have failed to discover any very decided case. The rocks of 

 the granite nucleus are certainly unfavourable to the preservation of 

 surface markings. At the head of Glen Sannox, however, there are 

 some fine examples of smoothed and polished rocks, and traces of 

 lateral moraines on both sides of the glen. Finely marked gravel 

 terraces occur at the mouth of Glen lorsa, in front of the Duke 

 of Hamilton's lodge, they have flat summits and steep sides, and 

 are elevated far above the action of any existing cause. Similar 

 terraces in Glen Catacol, and mounds at the mouths of Glen Eosie, 

 Clachan Glen, and others, may be deemed moraines by some. They 

 are, perhaps, rather due to the action of currents sweeping these 

 glens, when the area was rising from beneath the sea. The only case 

 of striation noticed was in the south section of the island, near the 

 waterfall in Glen Aisdale, two miles west of Whiting Bay. The rock 

 is a tough close-grained greenstone ; and the striation and grooving 

 are in a direction from west-south-west, slightly oblique to the valley, 

 which runs nearly east and west. Nowhere, however, are the phe- 

 nomena of surface boulders more strikingly exhibited. They occur 

 along the eastern shore in prodigious numbers and of enormous size, 

 somewhat larger in proximity to the granite nucleus ; but still of 

 huge proportions at Corrygills, and Whiting Bay, three to eight miles 

 from the parent rock ; and over the interior of the island, they strew 

 the surface at all altitudes. 



IV. CAEBONIFEEOUS EOCKS. 



14. The carboniferous system of Scotland, which attains so vast 

 a development in the basin of the Clyde and adjoining tracts, 

 presents some peculiarities and departures from the normal type, 

 as exhibited in England and Ireland. The entire area occupied by 

 the coal measures is, in the geological sense, but a single basin, with 

 the sole exception of a limited area to the extreme south-east, to 

 be presently noticed. Across the broad zone which reaches from 

 St. Andrews and Dunbar on the east, to Ardrossan and the heads 

 of Ayr on the west, the older rocks, on which the coal measures- 

 repose, nowhere rise to the surface so as to form "independent basins."' 

 Eidges of trap rocks do indeed intersect the area in various directions, 

 but cannot be said to cut it off into distinct basins. The coal tracts- 

 of the Forth are continuous with those of Clydesdale, while the 

 latter are confluent with those of Eenfrew and Ayr, at either 



