Dr Hibbert on the Rocks of Shetland. 69 
STRATA CONNECTED WITH THE LIMESTONE OF TINGWALL AND 
CATFIRTH VOE. 
Here it is necessary previously to describe the mass of Lime- 
stone, since I consider it in the light of a nucleus, as affording 
attachments to the lateral edges of certain strata of Mica-slate 
and Gneiss, appearing at the same time to determine the extent 
and direction of their course. 
The Limestone of Tingwall and Catfirth Voe . — East of the 
islands of House and Trondra, first appears, as we trace it from 
the south, an important mass of hmestone, occasionally associa- 
ted with hornblende-slate. 
The form of the limestone, as represented in a horizontal sec- 
tion, is that of an elongated main trunk or body tapering to a 
point, from which are given off two easterly ramifications. The 
main trunk or body of the limestone may be traced in a direc- 
tion of N. 5® E. (which is at the same time nearly the direc- 
tion of the strata) from House Island to the Vale of Tingwall, 
and thence to the north of Catfirth Voe ; its length being about 
thirteen miles, and its greatest breadth about 1200 feet. The 
first easterly ramification which we observe, and which is deno- 
ted by a corresponding change in the direction of the strata, 
passes through the Channel of Laxfirth Voe to Glitness. The 
second ramification passes through Vassa Voe, and the small 
isthmus of Brough, where, like the first, it becomes lost by the 
approach of the sea. 
The Mica-slate in the Peninsidar Tract (f Eswich and GliU 
ness ^ south-east of Vassa Voe . — The mica-slate thus geographi- 
cally described, may be also traced from the Mainland to the 
distant rocks named Grief Skerry, Rumble Island, Linga, and 
Isbaster. These strata afford an example in their junction 
with the limestone, of a circumstance of relative position which I 
formerly described. Here the lateral edges of the strata of mi- 
ca-slate are so opposed to the lateral planes of the strata of lime- 
stone, as to be intercepted by them. The general course of the 
strata of mica-slate, is from the main trunk or body of the lime- 
stone (if I may so name it), also from the southerly ramifica- 
tion of the limestone which passes through Laxfirth Voe and 
Glitness, to that northerly ramification, described as passing 
through Vassa Voe and Brough, by which it is intercepted. 
