SOi Br Hibbert on tfie Distrihutioii 
deep form of the sienite, traced from any given point in the sec- 
tion, precisely the same inclination with our horizon will be pre- 
served ; the only pecessary change in the condition of the stratum ^ 
will consist in a prolongation or abbreviation of its substance to 
meet any varied form which the sienite may have assumed. Thus 
the horizontal inclination which a stratum exhibits in its lateral 
plane, is perfectly independent of the form of the rock which 
merely affords to its lateral edge an attachment. It is for these 
reasons that I have hitherto used the general word attachment in 
expressing the junction of strata, since, in the application, is in- 
volved no supposed form of an unstratified rock, which, judg- 
ing from the angles made with the horizon, has, I apprehend^ 
too often, in laying down vertical sections of a district, been at- 
tended with erroneous deductions. 
I have dwelt at some length on the system of rocks at Fit- 
ful Head, for no other purpose than for the sake of obtaining 
precise ideas respecting the circumstances of stratification, to 
which we may apply the terms conformable or uncwvfbrmahle. 
The word conformable^ I have thus applied to all strata, that 
are from observation found to be attached together by their 
sides, or, in synonymous terms, to be collateral to each other ; on 
the other hand, only one circumstance of unconformity, among 
certain others peculiar to rocks, has yet been fully shewn, which 
is, when strata are opposed by their lateral edges to an unstra- 
tified rock. At the same time, it must be observed, that the 
stratification of the rocks of Fitful Head, is too confused, from 
the causes pointed out, to be recommended for actual observa- 
tion, as the best illustration of the views now entertained. Much 
better examples will be noticed in the progress of this demon- 
stration. 
The Sandstone and Conglomerate Roeks cf the South-east of 
Shetland. 
Leaving for a short time the rocks to the north of the Epi- 
dotic Sienite of Queiidal, I shall proceed to notice the Sandstone 
of the east of Shetland as it first appears, in tracing it from the 
south, at the neighbouring promontory of Sumburgh Head. This 
sandstone dilfers from one occurring more westerly, by admit- 
ting into its composition no portions or apparent fragments ei- 
