of the Rocks of Shetland. 79 
ing that channel from Busta Voe ; and, lastly, we return to its 
southerly origin at the grounds near Busta. The sienite, as we 
thus trace it, is 33 miles in circumference. Its utmost length is 
12, and its greatest breadth is 8 miles. 
At Tofts Voe, and in the islands of Yell Sound, this mass of 
sienite has a conglomerated structure, containing large appa- 
rent angular fragments of hornblende, some also being so round- 
ed, as to impress upon the mind, at first sight, the existence of 
water-worn pebbles. This notion will, however, receive little 
support from the frequent graduation of such apparent pebbles 
into the substance of the containing mass. A circumstance most 
meriting attention in our examination of this rock, is the Occa- 
sional appearance of strata of gneiss in the very centre of the 
sienitic mass. Such strata are, however, of inconsiderable extent, 
seldom exceeding a quarter or half a mile in breadth. This 
manifestation of included strata of gneiss, is observable near 
Tofts Voe and Brough, on the shores of Yell Sound. 
Gneiss and Mica- slate between Hagrasetter Voe and Daley's Voe, 
— These strata, bounded on the west by part of Hagrasetter Voe, 
and on the east by Dale’s Voe, may be traced in the northerly 
direction from their attachments to the sienite of Olnasfirth Voe. 
They thus maintain a course from the sienite of Olnasfirth 
Voe, to the sienite of Hagrasetter Voe and Yell Sound. 
The strata consist for the most part of gneiss, but to the east 
the felspar becomes evanescent, and we have rocks possessing 
more the character of mica-slate. The strata to the west have a di- 
rection of about N. 15° E. ; but as we cross them from west to 
east, the direction varies accordingly, by being more easterly 
also. The dip is to the west, at angles from 45° to 70°. 
I have at length concluded my account of the strata connect- 
ed with the sienitic and limestone masses of the central districts 
of Shetland, with the exception of strata deriving their course 
from the northerly bounding side of the sienite of Yell Sound, 
and certain strata to the west of that part of the epidotic sienite 
which extends from Sand Voe to Aith Voe. These rocks will 
be described in bringing to notice other mountain masses, pos- 
sessing in hke manner the character of nuclei. 
( To he continued.) 
