156 Messrs. Hicks and Davies— 
disposed to refer it to the species microcline. It occurs as single 
crystals, or as a line of contiguous crystals having an irregular but 
perceptible parallelism with the quartz. The mica is much altered, 
but from its marked dichroism it would appear to be biotite ; a little 
monochromatic mica (muscovite?) is also present. The mica is dis- 
tributed throughout, and only here and there does it appear grouped 
into thin bands. Sphene is present here also, with a little garnet 
and some magnetite.—T.D. | 
[Nore 8.—A close medium-grained rock with much red felspar, 
dark-coloured mica, and a soft yellowish-green substance resembling 
some varieties of ripidolite; but little quartz visible. When ex- 
amined in thin section, a greyish-red felspar, much decomposed, is 
found to constitute the larger part of the rock. It bears the aspect 
of orthoclase. Quartz is in exceedingly small amount in this rock, 
and appears only as an occasional occupant of interstices between 
the felspar crystals, or inclosed in them. The mica, which is con- 
siderably altered, is almost opaque, exhibiting only in places a dis- 
tinct dichroism. A serpentinous mineral of a clear yellowish-green 
colour, lying like the mica in distinct bands, is abundant. From its 
crystal contours, and the manner in which it is associated with the 
felspar, it is probably a pseudomorph after hornblende, though no 
trace of this mineral is now discernible. It is but faintly doubly 
refracting, and exhibits with polarized light a mosaic-coloured ground. 
Much of a black opaque mineral in minute grains, probably mag- 
netite, is distributed through and around this mineral. Garnet in 
ie is frequent. Evidently a highly felspathic gneiss. 
—T.D. 
Similar gneisses to those above described are found also along the 
N.E. shores, especially towards the eastern end. For some distance, 
about the middle, a thick band of limestone is traceable, and at 
Ben-Lair hornblende strata prevail. The following description is 
given by Murchison and Geikie! of the rocks along this shore :—“ On 
the right bank of Loch Maree this gneiss (older) contains both 
limestone and ironstone, which occur in bands regularly interstratified, 
and which have the normal strike of these ancient beds, as in the 
outer Hebrides. This strike from N.W. to §.E. is therefore parallel 
to the great depression occupied by the water of Loch Maree. In 
no portion of the North-Western Highlands is there a track which 
more completely exhibits the entire independence of this Laurentian 
gneiss of all those overlying deposits, also termed gneiss, with which 
Prof. Nicol has recently sought to identify it. .... We therefore 
call special attention not only to the N.W. strike of the beds of this 
fundamental rock, as contrasted with the north-easterly strike of the 
eastern rocks, but also to the marked distinctions in lithological com- 
position between it and any of the overlying masses.” Again,” “ In 
short, between Loch Maree and the sea-board at Gaerloch, wherever 
the fundamental gneiss is uncovered in low masses beneath the. 
Superjacent masses of Cambrian sandstone, the persistence of the 
1 Quart. Journ. Geol. Soc. vol. xvii. p. 176. 2 Tbid. p. 178. 
