VICINITY OF THE UPPER PAET OF LOCH MAEEE. 99 



planes. Orthoclase, microcline (often fairly abundant), and plagio- 

 clase (? oligoclase) can be recognized. Characteristic crystals of the 

 last are not very common. The quartzose fragments are sometimes 

 either a highly altered quartzite or bits from stratulee of this nature in 

 a gneiss ; certain of them (especially in the specimens from Torridon) 

 have a schistose structure*. There are also a few fragments resem- 

 bling a rather decomposed fine-grained slaty rock. I am not able 

 to detect any indubitably fragmental mica or hornblende, and must 

 be content to call the green mineral which is sparingly present in 

 the matrix, and almost certainly a secondary product, by the vague 

 term viridite. This matrix resembles a very fine sandy mud, gene- 

 rally much stained with ferrite and rather altered. The change is 

 most conspicuous in the second of the above specimens, which was 

 selected because it had a more marked appearance of alteration than 

 was usual. 



(4) Tlie Quartzite. 



I again refer to the works of earlier observers for the macroscopic 

 characters of this rock. As its variations in this district appear un- 

 important, I have only examined two specimens, one from the right 

 bank of Loch Maree, a typical example of the pure white variety so 

 abundant on both sides of the head of that lake, the other a slightly 

 yellower and more granular quartzite from the Gairloch road, about 

 three miles from Kinlochewe. The first is composed chiefly of quartz 

 grains, rather irregular in size and form, containing a fair amount of 

 microscopic " dust," and with a minute quantity of ferrite now and 

 then interspersed. The edges of the quartz grains are commonly 

 " fused " together, as is usual in highly altered quartzites, the one 

 bein^ irregularly indented into the other, as if the two had been 

 pressed together when in a slightly viscous condition. A few small 

 fragments of felspar can be recognized, resembling that in the last 

 series. Cracks traverse the slide, filled apparently with minute frag- 

 ments of the rock itself, cemented by secondary quartz, perhaps indi- 

 cating local crushing of the mass. In the other specimen the only 

 difi'erence worthy of note is that the grains are a little larger in size and 

 more irregular in shape ; that no felspar can be recognized, though 

 an earthy dark-stained mineral, generally torn away in grinding, pro- 

 bably indicates that it has been present ; and there are little scattered 

 clots of ferrite, and a few specks of a pale hornblendic mineral f. A 

 slice from the " fucoidal " quartzite has also been examined. Except 

 that there is more fine silty matter among the quartz grains, there 



* I have examined microscopically a fragment from a block (perhaps 2 cubic 

 feet) in a remarkable breccia north of the Loch-Maree hotel. It consists mainly 

 of quartz, in rather minute grains, with occasionally larger grains (of very irre- 

 gular outline) of felspar, with wavy microliths interbanded, scales of iron glance, 

 a fair quantity of epidote, and a little white mica. It is therefore a highly 

 altered schisty felspathic quartzite. 



t I did not examine into the disputed question of the conformity or uncon- 

 formity of the quartzites and Torridon Sandstone ; the general appearance of 

 the two suggests the latter, as maintained by Sir R. Murchison ; but my friend 

 Mr. L. Ewbank, Fellow of Clare College, teUs me that near Dundonnel (Little 



h2 



