1852.] NICOL ON THE GEOLOGY OF CANTYRE. 421 



that I should hardly have thought of noticing the fact had it not 

 been for some other connected points. One of these is the long 

 period during which the land appears to have remained stationary at 

 its former level. All round the Mull of Cantyre the ancient sea-line 

 is marked by lofty precipitous cliffs, hollowed out in many places 

 into deep caves. Even where they occur in the red sandstones, 

 limestones, or softer trap-rocks, these sea-worn caves are well calcu- 

 lated to excite surprise. But this is far more the case where they 

 have been excavated in a hard rock like the porphyries of Davar 

 Island. The effects of sea-action on this isolated rock are exceedingly 

 interesting. On the north-west side, which is turned to the land or 

 mouth of the harbour, the island slopes gradually to the sea-level, 

 and the ancient beach is scarcely marked by a slight notch or inden- 

 tation. On the eastern side, turned to the open Firth, it is sur- 

 rounded by high bold cliffs of rudely prismatic porphyry. Below 

 this vertical wall, a horizontal ledge of rock extends outwards for 

 fifty yards or more, and is covered in most places at high water, but 

 is dry at ebb tide. This ledge also terminates abruptly in another 

 vertical wall, the water, on one occasion when I visited it, being about 

 four feet below its edge, but still apparently very deep. Its surface is 

 strewed with huge, well-rounded blocks of porphyry, which almost 

 disappear near the outer margin, but become more abundant near the 

 foot of the cliff. Boulders of 12 to 18 inches in diameter are very 

 common, and are usually thoroughly rounded, showing that the 

 waves have no difficulty in moving stones of that size. When from 

 4 to 6 feet in diameter the blocks are generally more cubical and only 

 the corners worn off, but even then they are evidently yielding to the 

 abrading influences of the sea. On the south-east, or most exposed 

 side of the island, the ledge seems to be rapidly disappearing, and 

 the rounded boulders covering it are fewer than on the northern side 

 where the wave-action is less. In the latter place the ledge is wider, 

 and the blocks form thick heaps, apparently arranged in two or three 

 rows or beaches. 



These facts show the present action of the sea obliterating, as it were, 

 the traces of its action in former times. The old and new beaches 

 will sooner or later coincide, and all record of the former be then 

 wholly destroyed. To judge from appearances, the sea must have 

 stood much longer at the higher level than it has at its present ele- 

 vation. In the wall of rock above this ledge, and quite beyond the 

 action of the waves at the present time, many caves occur. One of 

 these with a double mouth, or rather two caves meeting in the in- 

 terior, measured 130 feet in length. Its sides and bottom were 

 smooth and worn as if by the beating of the waves, and the heaps of 

 well-rounded stones, covering the floor in many places, showed the 

 tools by which this immense excavation had been chiselled out of the 

 solid rock. Fragments of recent shells were lying on the floor, but 

 probably carried in by men or by the sea-fowl, which, with flocks of 

 wild pigeons, had their nests in crevices of the lofty walls. When the 

 waves beat into this cave, the sea must have been at least 30 feet 

 relatively higher than at present. Even though some fissure in the 



