476 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
the unaltered material beneath having the finest green colour, and the clearest 
vitrzous lustre of any specimens I have seen from the Cuchullins. 
The specimen which showed the semi-metallic lustre to the greatest depth 
in splitting it up was a loose crystal which I got from GriEVE ;* this was from | 
Drum na Raave, and its analysis is given. It was about an inch in thickness; 
the small amount of metallic lustre it possessed gradually, in the inner parts of | 
the stone, merged into a dull brown, and finally into a dirty green. | 
As regards toughness, this is a property which it does not, when separated | 
from the rock, possess in any marked degree ; it may be readily split along its 
cleavages, bruised by a hammer, or powdered in a mortar. . 
The rock as a whole is somewhat tough in its exterior layers, but not more | 
so than the rock in Rum, and very much less so than many rocks of a somewhat | 
similar type. . 
The external toughness which the rock presents is doubtless due to surface | 
peroxidation, which cements the granules of the rock; and, acting like a “pan,” | 
or like bog iron ore, excludes in greater part the falling water, and so, preserving : 
it from decay, enables it to a great extent to present that appearance of inde- | 
structibility which may have influenced Dr Maccuttocn when assigning to it a | 
name. . 
As my analyses show that the mineral is merely augite of a composition | 
very similar to that of Rum, the question now is, what are we to call the rock | 
which contains it ? | 
The mineral it was, which was supposed by Dr Maccuttocu to confer upon | 
the rock its toughness; and so, from the mineral, the rock was called hypersthenie. 
This has now been changed for the somewhat meaningless abbreviation of 
hyperite. 
There does not seem to be much judiciousness in attempting to change the | 
name. Similar rocks which occur elsewhere are known by it ; and although it | 
may prove to be the case that they also contain no true Paulite, yet there is 
no recognised name which can be altogether fittingly applied to it. 
Were we to be guided only by mineralogical characters, as it consists almost | 
solely of labradorite and augite, we would be constrained to call it dolerite; | 
but as no dolerite presents the same lithological features, and as from its posi- | 
tion and physical structure it has much the appearance of having been the | 
crystalline slag which plugged the void from whence active volcanic forces had | 
once operated,—filling up at the same time the rents resulting from their | 
operations,—it must rather be regarded as plutonic than a volcanic rock. 
Of such rocks it can only fall under either diabase or hyperite. Its freedom 
* My friend, who most generously made over to me the cherished gleanings of his many and even | — 
midnight wanderings among the Coolins,—repelling my slanders concerning the beautiful product of the | 
hills he loved so well,—put the most bronzy specimens remaining into the hands of a lapidary to be 
cut into brooches. He was horrified when the stone was returned to him in fragments, with the explana- 
tion that they were “all rotted.” 

