﻿Vol. 66.~] ABOUND THE BOSS OF MULL GRANITE. 377 



[It has been pointed out by Mr. G. Barrow that the intricate line 

 of junction with the gneisses is like those of the < Older Granites ' ; 

 but at the same time similar junctions (and also similar contact- 

 alteration) are known around Newer Granites, notably the granites 

 of the Glencoe district. 1 ] 



(b) The Moine Rocks. 



The Moine rocks occupy an area of about 11 square miles, which 

 is bounded on the west by the granite intrusion, on the north-east 

 by the Bunessan Fault, which brings down the Tertiary plateau- 

 basalts, and on the north and south by the sea. 



These rocks are sharply folded, steeply inclined, and strike north- 

 north-eastwards. They may be conveniently divided into 



(1) a Psammitic Group, consisting chiefly of flaggy quartz-felspar granu- 



lites, with some thin beds of quartzose mica-schist; and 



(2) a Pelitic Group, consisting chiefly of garnetiferous mica-schists (or 



gneisses) which are often coarse and quartzose, alternating with beds 

 of fine, granulitic, micaceous quartzite and some thin bands of lime- 

 silicate rock. Epidiorite sills occur among these gneisses. 



The greater part of the ground is occupied by the rocks of Group 2, 

 but those of Group 1 form the more easterly portion and also a very 

 small tract in the extreme north-west of the Moine-rock area. 



The following is a brief description of the rocks passed over, 

 starting from the granite margin and travelling away from it east- 

 wards across the outcrop of the Moine Gneisses. The traverse starts 

 from the south-western corner of Loch na Lathaich along the coast- 

 section to Bunessan, and thence inland along the old cliffs of the 

 100-foot raised beach, which extends up to and along the south side 

 of Loch Assapol. 



At the starting-point the granite is in contact with the psam- 

 mitic Moine rocks, which here occupy a very small area between 

 the road and the sea (see map, fig. 1, p. 378). These quartz-felspar 

 granulites are similar to those of other districts, and probably 

 represent original arkose and sandstone. In places (chiefly in the 

 larger area in the south-eastern corner of the map) they are 

 coarser than usual, and indications of drawn-out pebbles suggest 

 that the rock was conglomeratic. The beds are parted by seams of 

 quartzose mica-schist, which may represent thin beds of shale 

 between the original sandstone. Near the granite the granulite 

 contains ungranulitized porphyritic crystals of felspar (see p. 385). 



Leaving the granulites, we pass eastwards across some beds of 

 white quartzite on to the pelitic Moine rocks, which here are chiefly 

 massive beds of coarsely-rumpled quartz-muscovite-biotite-gneiss. 

 Alternating with these are fine granulitic micaceous quartzites, beds 

 of dark, less quartzose mica-schist, and thin pale bands formed of 

 calc-silicate minerals. 



1 C. T. Clough, H. B. Maufe, & E. B. Bailey, Quart. Journ. Geol. Soc vol lxv 

 (1909) p. 611. X7 



Q. J. G. S. No. 263. 2 d 



