James Neilson — Old Red and Carboniferous of Arran. 157 



far beyond the limits of tlie United Kingdom and has engaged 

 many pens. In particular, Sedgwick and Murchison, 1 A. C. Ramsay, 2 

 Dr. James Bryce, 3 and others, have written of these particular rocks, 

 and all recognized, not only Old Red Sandstone, but also Car- 

 boniferous rocks, and their writings on the subject are full of most 

 interesting facts, with carefully reasoned deductions. 



The northern half of the Island of Arran consists, first, of a central 

 granite nucleus of somewhat circular form, which embraces all the 

 higher hills. This granite nowhere reaches the sea, being sur- 

 rounded by a complete ring of slate and schistose rocks. These 

 are overlain by another series of rocks, among which red is the 

 prevailing colour ; but the latter only form three-fourths of a circle. 

 Previous writers on Arran had assigned these latter rocks partly 

 to the Old Red Sandstone and partly to the Carboniferous form- 

 ations, and it is to them that we wish to direct attention, with 

 the view of going over the evidence already recorded, and also 

 of adding any observations we ourselves have been able to make. 

 Observation here is very much facilitated by the fact that the 

 intrusion of the granites (or final intrusion, if there were more than 

 one) occurred subsequent to the deposition of the highest of the 

 sedimentary rocks, which are elevated all round the coast, and their 

 edges being exposed b}' the tides afford unrivalled opportunities for 

 geological investigation. 



As was first pointed out by Sedgwick and Murchison, the lowest 

 of these Old Red Sandstone rocks on the beach are seen at North 

 Sannox, where there is an anticline from which the rocks dip 

 respectively to the north and south. They consist mostly of 

 red sandstones and conglomerates, and, as will readily be ac- 

 knowledged, the rocks north of the anticline correspond with those 

 to the south. Sedgwick and Murchison set down these rocks as 

 Old Red Sandstone, which, according to them, extended for about 

 three miles along the shore, the northern junction with the Car- 

 boniferous occurring to the north of the fallen rocks, and the 

 southern a quarter of a mile north of Corrie. 4 These rocks are 

 then overlain by Carboniferous rocks for several miles both north 

 and south, and are finally overlain by rocks of the New Red 

 Sandstone age. Ramsay also supports this theory, and Bryce only 

 differs from it in referring the uppermost rocks to the Upuer 

 Carboniferous instead of the New Red Sandstone. The writer's 

 own observation has led him to the conclusion that these writers 

 were mainly correct, and, although aware of Sir A. Geikie's views, 

 he yet did not feel justified in questioning them till he had an 

 opportunity of again traversing the ground. 



1 Proceedings of Geological Society of London, vol. i, p. 41 (1S28). This appears 

 to be only an abstract of their paper. 



2 " Geology of the Island of Arran," by (Sir) Andrew Crombie Ramsay, 1841. 



3 "Geology of Arran and other Clyde Islands," by James Bryce, M.A., LL.D., 

 4th edition, 1872. 



4 That is, 100 yards north of the great split boulder which forms such a conspicuous 

 object on the shore. 



