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ATA PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
lapped, and altered pre-existent liassic rocks ; to be in turn invaded and over- 
lapped by a series of rocks, up to this day termed hypersthenic. 
In Rum the inferences are more extended. Red sandstone rocks, assigned 
to the Cambrian epoch, and underlying beds conformable thereto, on three 
sides fell away from a central mass at high angles; on two of these sides these | 
rocks assume low angles, and a uniform strike and dip, at a short distance from 



that central mass. 
When in close contact with that mass they are fractured and altered ; and 
they are overlaid by that mass. That mass has the composition and the 
structural arrangement of recognised igneous rocks; and it contains zeolites, 
These masses, therefore, are igneous rocks,—in the first island manifestly 
more recent than the Lias; in the second as manifestly more recent. than the 
Cambrian. 
But, inasmuch as the earliest and the latest members of these rocks—the 
syenite, and the amygdaloids with basalts—are common to the two islands, 
while the intermediate members show but trifling lithological differences, if any, 
the conclusion may safely be drawn, that the two rock masses were, as a 
whole, contemporaneous ;—that, instead of being metamorphosed sediments 
of very great antiquity, they are eruptive rocks of comparatively very recent 
times. 
In adducing chemical evidence to show that the rock in Rum, termed 
augitic by Maccuttocg, is but a modification of that which occurs in Skye,—and 
to which, from its containing a mineral of supposed specific distinctiveness, he 
gave the name of hypersthene rock, since contracted into hyperite,—I have in 
the first place to refer to my paper on the Felspars. In this I have shown, by 
the analysis of specimens purposely received from the hands of others, that the 
felspar of the rock is labradorite. Though I have not yet analysed the felspar 
from the rock of Rum, I have no hesitation in pronouncing it to be the same. 
Crystals of the mineral may, at the north side of the summit of Haiskeval, be 
obtained over an inch in size in every direction. These are finely striated, very 
glassy and pellucid ; if they differ from the mineral elsewhere found in Scotland, 
it is only in their being finer in all respects. 
As regards the occurrence of the substance called hypersthene by MaAc- 
CULLOCH, and faultily analysed by Murr, it is to be observed that it is, in its 
lustrous slightly-bronzy form, by no means of common occurrence in the rocks 
of the Cuchullins, Maccuttoc# himself says that the large characteristic speci- 
mens only occur in veins; in which he himself likewise declares that it is 
to be found in Rum. If we except the known localities, these veins are so 
rare in the Cuchullins that I have never myself found one of them; or evena 
single bit of the characteristic mineral, except in loose blocks,—evidently 
portions of veins. 
MAaccuLLocH, it is true, maintains that it is the same mineral which, im 
