of Edinburgh, Session 1881-82. 
367 
a breccia is scarcely recognisable with the naked eye, though it 
becomes distinct when the rock is polished. In the latter condition 
it resembles clinkstone, as Macknight had shown. In its more 
distinctly brecciated form, it resembles serpentine; but it is quite 
unassailable with the point of the knife, while true serpentine is 
scratched with great ease. 
No one has yet tried to discover by modern methods the nature 
of the dark greenish-black matter which gives the rock of the 
precipice its characteristic colour, and which Macknight assumed to 
be hornblende. But Professor Geikie will probably be able to settle 
that question by examining, microscopically, fine transparent sections 
made according to the method of the late Mr. Nicol. 
It is singular that hitherto no one has tried whether the rocks of 
Ben Nevis can be put to use. Some curiosity-monger at least 
might have been thought desirous of attempting to produce some 
memorial of his visit to these curious monuments of ancient volcanic 
agency. He would then have been surprised by the discovery that 
all of them are ornamental stones of considerable and sometimes 
great beauty. 
In the autumn of 1880 my sons brought down to me from the 
very summit of the mountain a hand-specimen broken off from the 
solid rock, where it protruded through the surrounding wilderness 
of loose stones and blocks. The fresh fracture showed it to be a 
very pretty felstone-porphyrite ; and I felt sure it would prove a 
fine ornamental stone, if hard enough to take on a high polish. Our 
skilful lapidary, Mr. Sanderson, found it to be the hardest rock he 
had ever worked ; and he produced the little pyramid, which has 
been already shown to many members of this Society, to their 
entire satisfaction. Last autumn I resolved to obtain, if possible, 
larger masses of all the forms assumed by the rock of the precipice ; 
and my sons, entering into my wishes, brought down from their 
excursion, already mentioned, ample specimens for showing the 
characters of all the chief varieties, besides materials sufficient for 
exercising the ingenuity of Mr. Sanderson in constructing an 
obelisk, in which he has been eminently successful. These speci- 
mens are now exhibited to the Society. In the obelisk the first 
step of the basement is granitic-porphyrite, the second a well-marked 
felstone-porphyrite of the dark kind. The plinth is an equally 
