346 SECTIONAL TRANSACTIONS.— C. 



Arisaig. 1 The schists concerned lie not far to the east of the Moine Thrust. 

 They fall into three groups, as follows : — 



3. Upper Psammitic Group. 



J (c) Upper Striped Schists with calc- 



2. Striped and Pelitic Group (b) p^^gchisS!' 



[ (a) Lower Striped Schists. 

 1. Lower Psammitic Group. 



The above groups are here termed, collectively, the Morar Schists, and 

 form a single stratigraphical series with interbanding along their mutual 

 junctions. The original order of deposition is shown in the psammitic 

 schists by abundant false-bedding, by recurrent slip-folding, by ripple- 

 marking, local erosion and the downward penetration of sandy material 

 into fissures from an overlying bed. In the striped schists of Group 2, which 

 consist of alternating lamina? of psammitic and pelitic or semi-pelitic 

 material, false-bedding on a small scale and ripple-marking are sometimes 

 seen in the psammitic layers. 



Older beds are encountered in a direction eastwards from the coast with- 

 out repetition by folding of any consequence. The total thickness of the 

 Morar Schists must be immense. An estimate of 19,000 ft. has been made, 

 but no stratigraphical top or base to the series is known. 



The lowest group (1) is in contact eastwards with much crumpled and 

 folded schists or gneisses. These form an anticlinal core with N.-S. axis. 

 In Knoydart both to west and east Group (1) is succeeded by the Striped 

 and Pelitic Group (2), which on the eastern side is injected with granite- 

 pegmatite and thus forms injection-gneisses, which cover a wide area in 

 Knoydart and eastern Morar. 



The rocks of the anticlinal core are mainly paragneiss, but include a 

 broad belt in which hornblendic and feldspathic bands are prevalent. The 

 structural succession is as follows : — 



(d) Psammitic gneiss. 



(c) Striped pelitic-psammitic gneiss. 



(b) Banded hornblende-gneiss, etc. 



(a) Psammitic gneiss, with epidote-rich bands plentiful near top. 



Along the junction of the gneissic core with the Lower Psammitic Group 

 (1) of the Morar Schists, the Psammitic Gneiss (d) and the Striped Gneiss 

 (c) are locally absent. The junction appears to be a plane of discordance. 



Afternoon. 

 Excursion to Preston district. Leader, Mr. L. H. Tonks. 



Friday, September 11. 



Dr. O. H. Schindewolf. — Chapters from the phytogeny of the Cephalo- 

 poda (9.45). 



Discussion on The geomorphology of the Irish Sea Basin (10.15). 



Prof. J. K. Charlesworth. — Introduction. 



The Irish Sea Basin is the result of an age-long evolution. Tectonic 

 forces of Caledonian age raised the Lower Palaeozoic sediments into the 



1 Richey, J. E., in ' Summary of Progress for 1935, Part I ' (Mem. Geol. Surv.), 

 I93 6 . PP- 78-79- 



