368 
Proceedings of the Royal Society 
well-marked serpentinoid breccia. The shaft is also the same 
breccia, but so dark that its nature is scarcely recognisable in the 
rough state of the stone, or until it is finely polished, and viewed 
with bright light. The separate pyramid is felstone porphyrite, 
with its porphyrising felspar crystals very small. This is the only 
specimen taken from the solid rock. But any block or stone of the 
confusion covering the whole summit, or the slopes of the corries 
which cut the precipice, will furnish the curious with specimens 
equally characteristic ; for the weathering does not go deeper than 
the thickness of fine pasteboard. 
Let me add that any one who may be inclined to make the 
excursion to the base of the precipice, should by no means, unless 
himself an experienced mountaineer, attempt it without a good 
guide; for the way up the rugged precipitous glen, — chiefly on 
the south-west bank of the valley stream, the Allt’-a-Mhui (mill 
burn) linn, — is tortuous, scarcely marked, and, in the frequent un- 
expected mists of the mountain, such as would be apt to lead into 
embarrassment and danger. A good view of the whole precipice 
is obtained by crossing to the north-east bank of the stream when 
about 2000 feet above Fort- William. But the opportunity should 
not be lost of ascending into the Corrie-na-Ciste, opposite the 
beholder, about 1200 feet higher, and surrounding himself with a 
wild amphitheatre of shattered precipices, rocks, blocks, and stones, 
without any trace of the works or habits of man within his sight. 
2. On the State of Carbon in Iron and Steel : a New 
Hypothesis of the Hardening of Steel. By K. Sydney 
Marsden, D.Sc., F.B.S.E., &c. 
(Abstract.) 
This paper first treats of the composition and properties of the 
different kinds of iron, known as wrought iron, steel, and cast 
iron, and especially of the changes which steel undergoes on being 
heated to redness and then suddenly cooled by plunging it into 
water, mercury, or oil, and known as hardening ; also of the peculiar 
property known as tempering, by which the hardness and brittleness 
can be removed. 
