FKOM THE NOKTH-WFST HIGHLANDS. 



419 



stage is rotated, though occasionally an irregular nucleus appears to re- 

 main homogeneous. These give a streaky or somewhat foliated aspect 

 to the slide. There is a little sericite, which enhances this structure. 

 In 97, however, which contains a little haematite, some few original 

 clastic grains of quartz may be recognized, together with microcline. 

 I should suppose these rocks to be exceptional varieties of the quartzite 

 group ; but the obliteration of the characteristic structure, and the 

 resemblance to the quartzose part of many highly altered mica schists, 

 suggests that the rock may have been originally rather a fine-grained 

 sand or silt, and then, by the action of heat, pressure, and water, 

 almost reduced to a gelatinous silica ; so that, as in a schist, many of 

 the minute granules of quartz now visible are of secondary origin. 



Limestones. 



Of the sedimentary rocks there remain some limestones, more or 

 less crystalline. Although I do not think them of one geologic age, 

 I group them together because it is more difficult to conjecture from 

 its crystalline condition the age of a limestone than that of any 

 other sedimentary rock. 



69 (Durness). A rather impure limestone, slightly dolomitic ; no 

 distinct trace of organisms, but not more altered than one would 

 expect a Palaeozoic limestone to be. 



68 (Loch Ailsh). A crystalline limestone, somewhat dolomitized, 

 with a little fragmental quartz and less felspar. Towards the edges 

 of the slide, associated with a little chalcedonic quartz, are some 

 imperfectly developed crystals, above '02" long, colourless, of slightly 

 silky aspect, with two cleavages intersecting at about 80°, and an 

 extinction-angle of rather less than 20°, with the edges of the prisms 

 so defined. 



67 (Balloch). A generally similar rock, but without the last- 

 named mineral, and with rather more quartz. 



105 (South of Ben More Lodge, Loch Ailsh, p. 387). A calc-schist, 

 consisting of calcite or dolomite, quartz, probably both fragmental and 

 secondary, and a micaceous mineral, with some ferrite. 



106 (West of Ledbeg, p. 388). A specimen of the remarkable 

 marble discovered by Prof. Heddle. As this rock is now being investi- 

 gated by himself and others, I shall merely say that it has a finely 

 crystalline matrix of calcite, perhaj)s somewhat dolomitized, in which 

 are scattered, irregularly and often thickly, subangular to rounded 

 grains of a white pyroxene, probably malacolite, many of which are 

 partially converted into a serpentinous mineral. In one portion of 

 the slide is a structure resembling the "canal system" of Eozoon, 

 and, like it, more conspicuous where the calcareous mineral is less 

 distinctly crystallized. For the reason above given, I merely note 

 this fact. 



Igneous Bocks. 



71 (Traligill Burn, p. 409). This specimen has aground-mass of 

 rather microcrystalline felspar, plagioclase (so far as we can see in its 

 present condition) predominating in which occurs a considerable 



