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PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 487 
Going lower still, we may walk for tens of miles across the upturned edges 
of a rock, the beds of which strike vertically downwards with such an un- 
yarying determination of purpose that we are impressed with the whimsical 
fancy that if we ever again meet with them it must be when they come out at 
the other side. 
After many traverses of the formations mentioned, my experience does not 
enable me to indicate any one spot or bed which could afford an augite which 
is the representative of this. 
The Shinness limestone locality shows, throughout its great abundance, 
no trace of such a variety. I know of but a single doubtful occurrence of 
augite in the midst of the vast abundance of hornblende in the lower gneiss. 
The well-known conversion of hornblende into augite by heat may possibly 
account for its occurrence ; but in this case a double action is required. The 
a 
first—that by means of which the transmutation was effected—resulting in the 
production of the broadly cleavable masses. The second—that which produced 
the final vitrification of these masses. Of any such double action, we have here 
evidence only of the feebler—the vitrifying. 
The second part of our query, namely, the topmost limit of the heat to 
which the augitic lumps had been subjected, is more easily answered ; seeing 
that a near approximation may be arrived at by direct experiment. 
Many years ago I had an opportunity of determining the temperature to 
which fragments of different of the members of the lower coal measures had 
been subjected, when caught up among the ashes which form the small 
volcanic cones and necks around the shores of Fife. 
In the shore sections of the wave-worn bosses of tufa which stud the coast 
near Kinkell, much fragmentary matter of various description is to be seen 
promiscuously imbedded, and characteristically and instructively altered. 
The bituminous shales have lost all their illuminants; and, of organic 
matter, retain only the blackening stain of sparsely distributed carbonaceous 
| particles. 
_ The encrinal limestone has become granular and crystalline. 
The included freestone masses present themselves as a quartzite,—with 
firmly agglutinated grains, splintery fracture, elastic resiliance, and sonorous ring. 
Shivery masses of carbonaceous or “ black chalk ” clay show every stage of a 
| passage into Lydian stone; while volcanic bombs of the latter—perfect in the 
| transmutation—lie impacted in the encircling volcanic mud, with surfaces which 
exhibit rounding and abrasion. 
We have here abundance of material to work upon, in estimating the 
quantum of the energy expended in the production of these changes. 
Close observation of the altered calcareous fragments shows most clearly 
that the period of time during which they had been subjected to the heat 
