(^the Rochs of Shetland. SOS 
as having an inclined surface. Again, the surface, instead of 
being impendent or inclined, may be vertical. In the present 
instance, the sienitic rock in a deep section, formed on the 
coast by the rock gradually yielding to the inroads of the wes- 
tern ocean, exhibits to us a specimen of the impendent sur- 
face ; the sienite appearing to hang over the strata which are 
connected to it by their lateral edges. Geologists would pro- 
, bably express the relation by the word superjacent, as applied 
to the sienite. There is only one objection to the word super ^ 
jacent, that it assigns a fundamental character to the strata, and 
an incumbent character to the sienite ; notions v/hich cannot^ 
exist, as long as w^e can conceive that the sienite may shew every . 
variety of surface, as it is observable at different depths : at 
one certain depth it may be impendent, at another inclined, 
and at another vertical, these varieties so combining, as to give 
to the deep surface of the rock, were it exposed, a waved or 
zigzag appearance. Now, it is evident, that a prolongation or 
abbreviation of the substance of any individual stratum, to 
meet those varied forms of which we have supposed the si- 
enite to be susceptible, would, at every increasing depth of 
the section, exhibit to us the stratum and the mass of sienite 
by turns, in a superjacent, and in a subjacent position. Cer- 
tainly, in such a case, we cannot say of any individual rock, 
that it is both a fundamental and an incumbent one. It is surely 
more natural to conceive of strata when joined by their lateral 
edges to an unstratiiied mass, as exhibiting an irregular or un- 
certain line in their contact, like the suture by which portions 
of the human cranium are joined to each other. The words 
impendent or inclined may then properly represent only that 
part of the line of attachment which is visible to us, without re- 
lating to ideas of a position either fundamental or incumbent. 
There is an important inference arising from this view of the 
attachment of strata to an unstratified rock. A stratum has 
been conceived of, as attached by its lateral edge to a mass of 
sienite, or in other words, meeting it at any angle, which mass 
on the side affording such attachment, may be either vertical, 
or it may include or exclude a plumb line supposed to be sus- 
pended from the highest point of the attachment, being either 
impendent or inclined. Now, it is evident, that whatever be the 
X 9 . 
