1852.] NICOL ON THE GEOLOGY OF CANTYRE. 407 



connecting link between the newer rocks of Ireland and those remark- 

 able secondary deposits in the Western Isles, described in the valuable 

 memoirs of Sir R. Murchison and Professor Sedgwick*. 



It might have been expected that these peculiarities would have 

 attracted some geologist to visit and describe this portion of Scotland. 

 This, however, has not hitherto been the case, and no complete ac- 

 count of the geological structure of Cantyre has ever yet been pub- 

 lished. Some incidental notices of particular points may be found in 

 the Mineralogical Travels of Professor Jameson, and Dr. Macculloch 

 makes a few short references to it in his work on the Western Isles ; 

 the latter also published a description of the Porphyries of Davar 

 Island in the Transactions of the Society f. In the summer of 1850 

 I spent a few weeks in the vicinity of Campbeltown, and found many 

 very interesting geological phenomena well exposed in that neighbour- 

 hood. Some short notes of my observations were communicated to 

 the Meeting of the British Association at Edinburgh in August 1850, 

 and I had intended to communicate a fuller account of them to the 

 Geological Society, but always delayed in the hope of being able to 

 render them more complete by again visiting the locality ; but I have 

 hitherto been prevented doing so, and think it better to submit them 

 in their present form. My observations do not embrace the whole 

 peninsula, but refer only to its southern extremity, or the region ex- 

 tending from the Mull of Cantyre to a few miles north of Campbel- 

 town, a tract about fifteen miles in length by ten or twelve in breadth. 

 As I was not able to procure an accurate geographical map of the 

 district, or even a map of any kind on a large scale, it was not possible 

 to represent its geological structure correctly, and the sketch map 

 that accompanies this paper (Plate XXIII.) must be regarded as 

 merely a first approximation to a geological map. When I began 

 to examine the district, I believed Dr. Macculloch' s map to be a far 

 more accurate representation of the distribution of the rocks than it 

 proved to be on experience. It was only after I found that it was 

 wholly untrustworthy that I endeavoured to supply the deficiency, 

 and consequently was less able to do so correctly than if I had kept 

 this object in view from the commencement of my researches. 



In describing the geology of this district I shall begin with the 

 oldest or fundamental rock. This is the mica-slate, which, as shown 

 by the map, occurs in two detached regions J. The first of these near 

 Campbeltown is connected with the large mass of this rock which ex- 

 tends northward throughout the peninsula. It is almost divided into 

 two by the loch or bay of Campbeltown, but beds of mica-slate appear 

 in various parts of the low ground, rendering it probable that the rock 

 extends continuously from Ben Gollion on the south to the hills on the 

 north side of the bay. The second portion forms the wild country in 

 the south-west of the peninsula round the Mull. In both districts the 



* Trans. Geol. Soc. 2 Ser. vol. ii. p. 293 ; ibid. p. 353 ; vol. iii. p. 21 ; ibid. p. 125. 



t Trans. Geol. Soc. vol. ii. p. 423. 



X A third small portion of mica-slate is seen in the bed of the stream and the 

 low grounds above Southend Church, but too inconsiderable to be w^orth noticing 

 separately. See Map. 



