Vol. 59.] TORRIDONIAN, ETC. OF THE ISLE OP RUM. 191 



and at many places on the exposed tops of the moorland-hills (fig. 1). 

 In the shales contortion on a small scale is probably not less wide- 

 spread ; but it assumes a somewhat different form, which is apt to 

 elude cursory observation. The bedding is often seen to be affected 

 by extremely sharp zigzags, which are in fact small and very acute 

 isoclinal folds thrust over until their axial planes are nearly parallel 

 with the general direction of stratification. 



Fig. 1. — Torridonian sandstones on the shore at Camas 

 Pliasgaiy, Rum, 



[The appearance of regular dips is shown in strata which are nevertheless 

 highly contorted on a small scale.] 



The Torridonian strata are intersected by numerous intrusions of 

 peridotite and gabbro, omitted in the sketch-map (PI. XIV) in order 

 to avoid complication, and metamorphic effects are to be observed 

 in the immediate neighbourhood of these. The most universal and 

 conspicuous change consists in a decoloration of the red sandstones, 

 and the border of bleached rock surrounding the intrusive mass is 

 often visible at a distance. In contact with the more considerable 

 intrusive rock-masses, the sandstones have experienced meta- 

 morphism of a higher grade, involving partial reconstitution. Some 

 consist of recrystallized quartz and felspar, the latter in subordinate 

 amount, with some new-formed accessory mineral, usually brown 

 mica. Not infrequently the metamorphosed rock exhibits a certain 

 quasi-spherulitic structure, which is conspicuous on a weathered 

 surface. A good example is afforded by the altered sandstones 

 bordering apicrite-intrusion at Airidh Thalabhairt, on the north side 

 of Kinloch Grlen. Thin slices show that the felspar recrystallizes 

 more readily than the quartz, and often assumes a radiate arrange- 

 ment which gives the peculiar appearance just noticed. In this 

 recrystallized felspathic aggregate the quartz-grains are often seen 

 apparently unchanged. 



Besides the small plutonic intrusions, there are, in the relatively- 

 undisturbed Torridonian tract, very numerous dykes and sheets of 

 basalt. These have not, in general, given rise to any sensible 

 metamorphic effects. There are, however, certain remarkable 

 occurrences which call for special notice, since they have a bearing 

 on the connection between crushing and brecciation, on the one 

 hand, and igneous injection and metamorphism, on the other. 



In the tract under consideration the mechanical effects of crush- 

 ing are nowhere exhibited on the scale shown in the submontane 



