﻿502 PEOF. S. H. PvEYXOLDS OX THE [NoV. I908, 



considerably metamorphosed. At a distance of a few feet, however, 

 from the edge of the intrusion, a fault passes obliquely up the 

 quarry-face and is marked by a band of breccia. The presence 

 of this fault does not interrupt the progressive metamorphism of 

 the Old Eed, this probably indicating that it is of earlier date than 

 the intrusion. The fault-plane apparently forms the northern face 

 of the quarry for some 40 yards, but the exposures are very bad 

 here, the rocks being much obscured by talus and brambles. At 

 the end of this ill-exposed portion the northern face of the quarry 

 has been cut back some 10 feet from the fault-line, exposing a 

 section of Old Eed marl and sandstone, the lower beds of the marl 

 being thrown into slight undulations. The rock seen at this 

 portion of the quarry-face (which, owing to the cutting-back, lies at 

 a distance of some 18 feet from the edge of the dyke) is unaltered, 

 except that the prevalent red colour of the marl is more than 

 usually mottled with yeUow. A few feet nearer the dyke, however, 

 the marls begin to show signs of alteration; the red coloration 

 disappears; and the rock becomes at first in places pale yellow, 

 but in the main hard and purplish-grey with yellow spots and 

 patches, the appearance of which was suggestive of dolomite. 

 They proved, however, on chemical examination to be of not very 

 definite mineralogical composition, consisting mainly of silicate of 

 alumina and carbonate of lime, with only a subordinate quantity 

 of carbonate of magnesia.^ "Were it not for its softness, a hand- 

 specimen of the prevalent grey rock might, as was noticed by 

 Murchison, at first sight be taken for an igneous rock. Micro- 

 scopical examination of the altered marls showed smaU grains of 

 quartz and flakes of mica with much iron-staining, but did not disclose 

 any facts of importance. The sandstone does not commence to show 

 signs of alteration at so great a distance from the dyke as does 

 the marl ; but, as the line of contact with the trap is approached, 

 the sandstone and marl are strongly metamorphosed, the marl 

 becoming very hard and splintery, while the sandstone loses its red 

 colour and is rendered very hard and grey. Microscopical exami- 

 nation of this altered sandstone shows some interesting contact- 

 phenomena (PI. LIT, fig. 6), the quartz-grains being corroded and the 

 felspars recrystallized. Mr. Harker informs me that he is familiar 

 with this type of metamorphism in the Torridon Sandstone of Eum, 

 and has described it in the Geological-Survey memoir on the 

 ' Geology of the Small Isles of Inverness-shire ' ^ now in the press.^ 



(6) South of the trap. — On the southern side of the quarry, 

 where a thickness of about 12 feet of altered rock is exposed, 

 the contact-phenomena diff'er somewhat from those on the northern 

 side, as the sandstone is far less in evidence than the marl. The 

 latter rock, however shows alteration into a hard grey material 



1 I am indebted to my colleague, Mr, O. 0. M. Davis, B.Sc, for this 

 information. 



2 P. 13. 



^ Published subsequently to the reading of this paper. 



