98 PEor. T. G. bonnet's peteological notes on the 



In the first three cases the mineral is a green mica, probably an 

 altered biotite ; in the last, with a little of the same, we have chiefly 

 a silvery- white mica, showing brilliant tints with polarized light, 

 probably margarodite or paragonite. Hornblende (green) with very 

 characteristic cleavage and strong dichroism is plentiful in the spe- 

 cimens from near the Loch-Maree hotel, in a hornblende schist from 

 near the above-named locality, under Ben Slioch, and in a dark com- 

 pact schist in the bed of a burn to south of latter. There is also a 

 little in the above Glen-Laggan specimens, and more dubiously in 

 others. Epidote is present in the last, and in numerous well-formed 

 crystals in the first two. Few specimens are quite free from it. 

 Apatite is distinctly present in the first three of the above specimens, 

 and more dubiously in others. One of them (| mile from Loch- 

 Maree hotel) contains numerous crystalline grains of a yellow-brown 

 mineral, which I have little doubt is sphene ; and the same mineral 

 is present in other specimens. Opacite and grains of iron peroxide, 

 probably magnetite, occur in most in greater or less degree. 



Microscopically, then, as well as macroscopically, this group of 

 rocks has well-marked characteristics, which we also find, as we 

 might expect, in the gneiss of the vicinity of Stornoway*. There is 

 also a certain family likeness to the old gneissic rocks of Anglesey, 

 Caernarvonshire, the Wrekin, and the Malvern Hills ; and a resem- 

 blance may even be noted to specimens from "West Greenland and 

 the Lofoten Islands, not to mention yet more distant localities. 



(3) Torridon Sandstone. 



In the case of this rock also we may refer to the careful descrip- 

 tions of earlier observers. I examined it on both sides of Loch Maree, 

 over the district mentioned above, and at Loch Torridon. Striking 

 instances of the breccia of gneissic rock at its base can be seen by the 

 roadside north of Loch-Maree hotel, and on approaching the base of 

 Ben Slioch on the opposite shore. Commonly the sandstone is fairly 

 uniform in character, a hard grit composed of rolled grains of quartz 

 and red felspar, from J^" to -^q" in diameter, with a little of a green 

 mineral, being at first sight wonderfully like a fine-grained granite ; 

 but now and then it becomes coarse and pebbly — a very pretty variety, 

 with the rolled fragments as big as large peas, occurring in blocks by 

 the road to Gairloch, eight miles from Kinlochewe. Specimens for 

 microscopic examination were selected from the last-named rock, from 

 a spot on the same road nine miles from Kinlochewe, from the lower 

 part of the series (at two levels) on the right bank, near to the base 

 of Ben Slioch, and lastly from the shore near Torridon. With minor 

 differences in detail, their general character is the same. They con- 

 sist of fragments (usually well rolled) of quartz, felspar, and an 

 altered quartzose rock, in a fine granular matrix, in which some 

 secondary products have been formed. The quartz is generally rather 

 full of minute dusty-looking microliths. The felspar is often infil- 

 trated with f errite, which in some cases brings out clearly the cleavage- 



* The only other locality where I haye had opportunity of studying it in the 

 field. 



