472 Proceedings of Philosophical Societies. (June, 
introduced into the present paper only for the purpose of describing 
the best methods of obtaining sections of them in the direction of 
their natural joints. Of the other substances, not only the best 
methods of cleaving them are pointed out, but the results of their 
measurement by the reflecting goniometer are stated, and compared 
with those which have been obtained in the usual way by Bournon 
and Hauy. 
A supplementary notice on the Quartz Rock of Sky, by the 
President, was read. 
The rock in question forms a large mass of erect strata alternating 
with red sand-stone and greywacke schist. 
The latter strata extend in a north-east direction from one shore 
of the island to the other; but the quartz rock accompanies them 
only for about five miles. The structure of this quartz is for the 
most part compact, with a splintery fracture: occasionally it be- 
comes more or less granular, and now and then contains grains of 
felspar. 
Jan. 3, 1817.—At this meeting the reading of a paper by the 
President on the parallel Roads of Glenroy, was begun. 
Jan. 17.—At this meeting the reading of Dr. Macculloch’s paper 
was concluded. 
A long valley extends from the skirts of Ben Nevis to the mouth 
of the Spey, and is divided into two unequal portions by a low 
boggy hill of granite, that forms its summit level. On the south 
side of this hill is the source of the Spey, which flows to the south- 
east ; and on the north side is the source of the Roy, the waters of 
which flow north-west into the great Caledonian valley extending 
from Fort George to Fort William. On the sides of Glenroy, and 
of some of the lateral valleys, are traced strong lines parallel to each 
other and to the horizon. The two corresponding lines on each 
side of the valley coinciding precisely in level and elevation with 
each other. 
These lines have been attributed to various causes. By some they 
have been considered as the work of man; and by others as the 
effect of natural agents. 
Those who adopt the latter hypothesis agree in ascribing them to 
the action of water, on account of the perfect levelness of the 
lines, and their parallelism to each other and to the horizon; but 
they differ from one another in this respect, one party attributing 
them to the wearing of a torrent or current of the sea; and the 
other conceiving that the hypothesis of their having been the shores 
of a lake is better adapted to explain the present appearances. 
Into the consideration of all these hypotheses the author of this 
paper enters with much minuteness ; and though he considers the 
latter as the more probable theory, yet allows and states at large the 
difficulties which attend every mode of accounting for these remark- 
able phenomena. 
Feb. 21,—At this meeting a paper by George Cumberland, Esq. 
