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XXXIX. — On the Great Drift Beds with Shells in the South of Arran. By the 

 Rev. Robert Boog Watson. B.A., F.R.S.E., Hon Mem. Nat. Ver., Liiiieburg. 

 (Plates XXI., XXII.) 



(Read 4th January 1864.) 



The South of Arran in General. 

 Character of the Drift-Beds there. 

 Description of these in Detail. 



1. Auchinreach Burn. 



2. Glen Ashdale. 



3. Torlin Burn. 



4. Cloinoid Burn. 



5. Slaodrigh Burn, 



6. Crogcrever Burn. 



7. Clachan Glen. 

 Conclusions : — 



1. Boulder-clay derived from land glacia- 



tion. 



2. Ice covered the land till submerged. 



3. Boulder-clay deposited in the sea. 



4. „ compressed by ice, &c. 



Conclusions — (^continued.) 



5. Boulder clay contains land -formed beds. 



6. ,, deposited as land was sub- 

 siding. 



7. Subsidence extended to 1100 or 1200 ft. 



8. „ was continuous, not oscilla- 



tory. 



9. „ was gradual. 



10. „ was it rapid \ 



11. No general glaciation since re-emergence. 



12. Boulder-clay beds of all ages of glacial 



epoch. 



13. Drift and Boulder-clay contemporary. 



14. Relation to sea-line, a test of age. 



15. No material change on the basement- 



rock since glaciation. 



Summury. 



The whole southern part of Arran forms a field by itself, and whatever may 

 be the deeper connections of the agencies that have fashioned the north and the 

 south of the island, the result is a trappean area to the south, as distinct as if it 

 lay in another hemisphere from the north, with its granitic nucleus, and encom- 

 passing rings of stratified rock. 



This district is little visited, and is almost, if not quite, undescribed; it pre- 

 sents, however, much beautiful scenery, and for the geologist, problems of extreme 

 difficulty and interest, which deserve more attention than they have got. 



It may be divided into two belts of tilled land and moorland, above which 

 are the hill tops. This division corresponds roughly to three regions, the lowest 

 chiefly of sandstone, the middle where felstone prevails over the sandstone, and, 

 the highest of greenstone. 



From the sea, the land rises in a precipice, of from 50 to 200 feet in height. 

 In general, for some two or three miles up the valleys, the rock is sandstone with- 

 I out fossils, and of doubtful age, but probably Permian. It is soft, fine-grained, 

 I often shaley, thinly laminated, chiefly bright red or purple, and much intersected 

 though not much disturbed by dykes of igneous rock — large isolated masses of 

 which also occur. This sandstone region extends from the coast to a height of 

 from 300 to 500 feet. Its rising slope towards the interior is extremely gentle 

 both in the valley bottoms and in the hill sides above. 



VOL. XXIII. PAKT III. 7 c 



