of the Hocks of Shetland. 77 
on the Mainland. The strata dip to the west at a variety of 
angles, generally about 45°. 
Limestone of Ustaness .- — A mass of limestone, presenting in 
a horizontal section an elongated form, and tapering to a point, 
is interposed between the mica-slate of Beneness and the gneiss 
last described. It is eight miles long, and its greatest breadth 
exceeds sixteen hundred feet. The direction of the strata is 
nearly due north, varying some little from that of the strata on 
each side. That this interposed mass of limestone has the effect 
of intercepting strata, is shewn by a diminution of the breadth 
of the gneiss, to an extent corresponding to the space occupied 
by the limestone. 
3. Sti’ata maintaining a course from the southerly Mass of 
Epidotic Sienite to the Sienite of Olnasflrth Voe. 
Here a proper occasion is afforded for describing the sienite 
of Olnasflrth Voe : we shall then have two unstratifled masses 
made known to us, which, like nuclei, appear to determine 
the course of connecting strata. 
Sienite of Olnasfrth Voe . — That part of the mass which 
occupies the bed of Olnasflrth Voe, is distinguished by its dark 
colour, and by containing very little mica. But to the north 
and north-west of Olnasflrth Voe, another rock of sienite is an- 
nexed to it, which is characterised by the quantity of epidote 
which it contains. In this additional mass of epidotic sienite, 
there is much less hornblende and more felspar, than in those 
rocks of the same name which I have before described. The 
magnitude of the rocks taken collectively, may be estimated at 
five miles in length, and one mile in breadth. 
Micor-Slate of Weesdale Hill . — This rock is distinguished by 
the light colour of its mica ; it also contains some trifling quan- 
tity of felspar. The strata most unequivocally maintain a 
course from the epidotic sienite in the Bay of Scalloway to the 
sienite of Olnasflrth. In their course they form a chain of 
hills, which, with the exception of Ilonas Hill in North Mavine, 
are the highest in Shetland. The elevation of the hill at Wees- 
dale is estimated at about 1200 feet; Scallowfleld, a more 
northerly eminence, is somewhat higher, and there is a very 
considerable hill bounding Olnasflrth Voe. The direction of 
these strata is about N. 12° E., like that of the other rocks de- 
3 
