£98 
Dr Hibbert on the Distrihutwn 
vertical or inclined^ by which it is connected to other strata^ 
as the sides of a metallic lamella may be to other plates which 
are ranged in contact with it. A single stratum may also be 
represented as having two lateral edges of attachment ; strata 
being often found to be opposed to other rocks at their edges, in 
the same manner that we conceive of the edges of the me- 
tallic plates, which are opposed to the sides of a galvanic trough. 
In this instance, however, they are opposed at right angles ; 
but this angle may, of course, be varied ad libitum, to corre- 
spond to the different circumstances under which strata are 
found. A stratum may again be described as having a superior 
or upper edge ; though this term is perhaps superseded by the 
equally expressive language which we use, when we speak of 
the outgoings of strata. Again, the inferior edge of a stratum 
is illustrated by that of a metallic plate, which is opposed to the 
bottom of a galvanic trough. Of course, the relations of tlie in- 
ferior edges of strata must be often objects of mere speculation. 
If, lastly, any metallic plate of a galvanic trough be so altered 
in its position, that its planes become parallel to the plane of 
the horizon, it is evident that no other distinction of position 
can take place in it, or in a stratum under a similar condition, 
than that there should be a superior and irferior side, and 
certain horizontal edges 
But, besides these terms relating to the sides and edges of 
strata, other minutiae of description, when found requisite, will 
be introduced in the course of this paper. — I shall now, without 
further delay, attempt to explain the geological structure of the 
rocks of Shetland. 
Strata f Fitf id Head. 
Commencing our investigations at the most southerly part of 
Shetland, namely, at Quendal Bay, in the parish of Dunross- 
ness, a small system of strata, forming for the most part Fitful 
Head, on the v^est of the bay, will demand our earliest notice. 
Crossing the strata in a direction from east to west, we find 
on the west of Quendal Bay, gneiss traversed by numerous 
* The lateral edges of otjr author, are the ends of the strata of miners ; iiis sw- 
perior edges, their outgoings^ ; and inferior edges^ the bottoms of strata : and when 
he speaks of horizontal edgesy we are to understand the outgoings of horizontal stra~ 
ta. — Eq. 
/ 
