472 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
and towards Riesval, seen distinctly to overlie the augitic rock. In the north 
centre of Arstival a small patch of it is seen in the same position, but in no 
other part of the island is this bed, or the highly elevated layer of breccia which 
underlies it, to be seen. 
Ascending the north slopes of Halival,—on the second parallel,—we cross the } 
tilted beds of the flaggy, somewhat gneissic rock, which here rises into a shoulder 
some 1200 feet in height. A slight depression or transverse valley is imme- 
diately in front, before us there towers a grandly-terraced conical hill, hardly 
surpassed in characteristic outline by any spot in Faréde. Of this the boldly 
pronounced trappean beds dip very slightly to the west ; while, turning to look 
northward, we see the near bulk of the Cuchullins distinctly lined, from Gars- 
ven to Scuir na Gabhar, with three great belts of rock, likewise dipping slightly 
to the west. 
Descending into the transverse depression, we suddenly come upon the 
denuded bank of a bed of breccia, lying directly on the edges of the strata of 
the sedimentary rock. 
This is what Maccuuuocu refers to as his second breccia, considering it as 
probably a portion of a vein, posterior to the overlying rock. 
This cannot be conceded: the imbedded fragments consist solely of the 
underlying rocks,—egrits, cherty lumps, and sandstones ; not a particle of the 
augitic compound is to be seen; the paste, relatively small in amount, is 
felspathic and scoriaceous ; and it is a bed which is overlaid by, and altered at 
its point of contact with the lowest of the augitic bands. 
Moreover, it is laced in all directions by tortuous veins of aphanite, resem- 
bling Lydian stone. These do not enter the overlying rock, and therefore in all 
probability have been an exfiltration from the breccia itself, antecedent to its 
envelopment. 
Neither could it have been an zntrusive sheet, thrust between the augite | 
rock and the tilted strata ;—the sharp casting which the augite has taken of | 
the rough floor on which it lies, amounting in places to an interlocking of the | 
two, forbids such a view. Before it could be tenable that there had been a | 
forcible insinuation of so extended a sheet, the relative quantity of paste to | 
fragmentary matter in the intruding mass should be very great ;—that frag- | 
mentary matter should also indiscriminately contain augite and schist alike; | 
a mass so intruded could not possibly contain the red sandstone ; and, lastly, | 
on such a view, the brecciated bed should have affected the augite rock,—but 
in it no change is visible. 
Gravel beds of loose augite crystals lie glancing in the sun, with splendent 
but never bronzy lustre; and during the scaling of the cliff-capped terraces, 
abundance of loose rough crystals of glassy striated labradorite may be got. 
One bed of pure labradorite also occurs, it is a mass of small crystal in sugar- 
loaf arrangement. 

