l74 
PRIMITIVE DISTRICT 
from SE. to NW., commencing with the harbour of 
Stromness, and running through the high hill above that 
town to a place called Yeskanaby, on the west coast of Po-- 
mona, two miles on this side of the house of Skail. Here 
it terminates in a high mural precipice overhanging the 
sea, and, to the north, is immediately succeeded by the 
common greywacke-slate, and by a greyish sandstone, 
which, from its hardness and crystalline texture, is the 
only stone of that kind used for mill-stones in the whole 
island. Perhaps its vicinity to the strata of primitive gneiss 
may have given it these superior qualities. 
From this point of Yeskanaby we traced the gneiss 
(which is of the common grey kind, traversed by numer- 
ous veins of felspar and quartz) in a continuous and un- 
interrupted line back all the way to Stromness, and thus 
found its greatest length to be from six to eight miles. 
Its utmost breadth lies between the Island of Grsemsay, 
which is partly formed of gneiss, and the Bridge of Wae, 
where the road crosses Loch Stennis, in the direction of 
Kirkwall. I also thought that this breadth might be still 
greater, from an expectation that gneiss formed the funda- 
mental rock of Hoy, founded on a report that gneiss or 
granite had been seen near Rack wick, oh the south-western 
side of this latter island. Of this, however, we could ob- 
serve no confirmation, but noticed at the same spot a large 
bed of greenstone among the strata of red sandstone. The 
lateral extent of the gneiss, therefore, does not exceed two 
or three, or at the utmost four, miles ; and even this, as 
we approach its northern extremity, near Skail, gradually 
tapers to 100 or 200 yards. 
From having thus traced the boundaries of the primitive 
district in the Orkneys, we may presume that no strata of 
that class will be found in the Island of Pomona, or Main- 
land of Orkney, to the north of Yeskanaby or Skail ; for 
