PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 455 
“ Rough, rounded, and broken lumps.” The words well describe them as 
hand specimens. We will consider these features in a different order, 
that we may see what they teach. “Broken”; “‘rough” because broken ; 
and ‘“rounded”—that is, partially rounded, or they would not still be rough,— 
rounded on account of some attriting action which operated after they had 
been broken. 
Evidence of their having been broken, 2.¢., that they are the fragments of a 
larger mass. Mere roughness could not prove this ; the steam holes of igneous 
rocks, though usually more or less spherical, and presenting rounded or curved 
outlines, are not invariably so; so that a mineral which ultimately plugged these, 
through endosmose, would, in the taking a cast of a rough cavity, assume a 
rough outline; while again, if the augite, after thorough fusion, was on the 
abstraction of the heat to assume the solid state, while the rock matrix was 
still im a plastic condition, it might form a confusedly crystalline mass with 
rough surfaces. 
That the roughness of outline is not here to be so explained, but is really 
due to irregularity of fracture, is shown, jirst, by large and fairly brilliant 
cleavages of the augite abutting against what have been the sides of the 
masses, as shown by a thin investing layer of calcite and skin of saponite ; and 
abutting at an angle to these sides, which could be formed neither by a crystal- 
line arrangement which radiated from the sides of a cavity, nor by one radiating 
from the centre of the mass. The above cleavages, secondly, are of such a size 
as show that they must have originally belonged to masses of much greater 
dimensions than those in which they are now found. And thirdly, the rough 
- fractured sides occasionally exhibit—as also do internal fractures—portions of 
: 
| 
erystals of a size much too great to have been formed during the solidification 
of masses so small as these. 
As regards the rounding, it amounts in general to little more than the 
abrasion of the protruding cleavage angles, not to the giving a rounded outline 
to the general mass. As the surfaces are now covered with a thin coating of 
calcite, the nature of the abrasions cannot be seen; it certainly has not been of 
_ the continuous nature of wave battering, or river grinding, or sand blowing. 
As regards internal structure, there is here the same confused and hackly 
fissuring described in the Elie mineral, the fissures being however narrower, 
and the whole mass more coherent. These fissures are, for the most part, filled 
With saponite (?)—the probable result of incipient change,—and rarely with 
calcite. 
The recent fractures are, like those of the Elie, conchoidal; though here 
and there true cleavages in broad sheets cross the conchoidal fractures, and 
"even lie in directions non-accordant with the cleavages of the less altered 
| portions of the mass. These latter have been, in fact, posterior to the 
VOL. XXVIII, PART Il. 6K 
