SECTIONAL TRANSACTIONS.— C. 423 



extent by a complex of moved Cambro-Ordovician, which is exposed at the 

 head of Loch Kishorn and again in the Suardal Anticlines of Skye and in a 

 window east of Ord. The top of the Kishorn Nappe is furnished by the 

 base of the Moine Nappe, except near the Point of Sleat, where the 

 Tarskavaig Nappes intervene (Sheets 71, 61). 



A great inversion, called the Loch Alsh Inversion, is the main structural 

 feature within the Kishorn Nappe. It is part of a recumbent fold that runs 

 obliquely to the course of the Kishorn and Moine thrusts, that truncate it 

 from below and above. Thus at Loch Kishorn, only the upper inverted 

 limb of the recumbent fold is preserved ; at Loch Alsh, both limbs occur ; 

 while in most of Sleat, only the lower normal limb is found. The upper 

 limb shows a cleavage, or foliation, that scarcely penetrates at all into the 

 lower limb, and with this foliation there is in places mineral development 

 leading to a production of minute micas, including brown biotite. 



The generally normal lower limb of the Loch Alsh Fold develops an 

 additional local recumbent fold exposed west of Ord, near the window 

 already mentioned. The inversion connected with this Ord Fold is un- 

 accompanied by cleavage or metamorphism. Moreover, it does not extend 

 up to the base of the overlying Tarskavaig Nappes. 



The Tarskavaig Nappes emerge from under the Moine Thrust, and agree 

 in structural position with the Loch Alsh Inversion, except that they have 

 travelled forward by thrusting rather than inversion (c/., however, the 

 Balmacara Thrust of the Loch Alsh district). Their metamorphic grade is 

 closely comparable with that of parts of the Loch Alsh Inversion. It is true 

 that in addition to a widespread development of minute biotite, in part 

 brown, Clough found i mm. garnets at one locality; but these latter, after 

 separation by A. F. Hallimond, have been analysed by C. O. Harvey, and 

 proved to contain sufficient manganese to be natural associates of biotite 

 in its early stages of formation. The writer feels that the correlation of the 

 Tarskavaig ' Moines ' with the Torridonian, a view favoured by Peach, Read 

 and others, is distinctly strengthened. He welcomes the altogether new 

 evidence furnished by F. C. Phillips during the current session of the B.A. 



It is hoped to expand this account in a forthcoming Geological Survey 

 Bulletin. 



Dr. E. B. Bailey, F.R.S. — Tectonics, erosion and deposition (10.30). 



(i) Antecedent Drainage. — In maturity antecedent drainage often looks 

 wellnigh unbelievable, for it seems like special pleading to speak of a 

 barrier of hard rock raised so slowly as not to divert a river of soft water. 

 One is apt to forget that during early stages of mountain elevation a river 

 may have to cope with nothing more resistant than sand and clay. By the 

 time it reaches hard core rocks it may already be entrenched in a valley 

 thousands of feet deep, and therefore able to defy intermittent attacks by 

 earth movement, however strong the material that is employed. This sort 

 of relation is illustrated in some of the anticlines associated with the 

 Caucasus. 



(2) Cross-mountain Contrasts. — Sometimes the two sides of a mountain 

 chain, great as the Urals or small as the Malverns, show a wonderful con- 

 trast. On the one side the junction between the mountain-rocks and those 

 of the adjacent plain may be tectonic, and on the other side, erosional. As 

 a broad generalisation this is illustrated at the junction of the Urals, west- 

 wards with the Palaeozoics of the Russian Platform and eastwards with the 

 Tertiaries and Quaternaries of Asia ; or at the junction of the Malverns, 

 westwards with the Old Red of Hereford and eastwards with the New Red 



