(^the Rocks of Shetland. -60'7 
eonglomerate rock, which surface may be Yariously illustrated by 
any position or inclination given to the subjacent lamellae in the 
trough, agreeably to the variety in this respect, which exists in 
nature among strata. But care is to be taken, at the same time, 
that the lower edges of the superimposed lamellae are in actual 
contact with the surface formed by the upper edges of the sub- 
jacent galvanic plates. For it is an important circumstance if 
it shall be found to exist in other countries no less than in Shet- 
land, that the attachments of strata to rocks of a different kind 
on which they repose, should necessarily involve the contact of 
their inferior edges. 
I may here also observe, that if strata were deposited on a 
fundamental rock like the coats of an onion, to which they have 
been often compared, it is evident that only the lowest stratum 
in any series would come in contact with the mass affording 
them a basis, which attachment would take place from the con- 
tact of the lowest side of the stratum next to the fundamental 
fock, and not from that of its inferior edge. But, according to 
the views now entertained, there is not an individual stratum to 
he found in this series of conglomerate strata^ thad does not hy 
its inferior edge come in contact with the fundamental surface 
'which is common to them 
^thly^ The greatest diversities of inclination, at every step 
which we take to examine the strata at present under considera- 
tion, are constantly occurring. To account for these diversities, 
we must assume, that the irregular thicloiess of the strata, as 
observable in their outgoings, is continued in the same manner 
throughout their whole depth. An irregular thickness of the 
strata may be explained by the tabular seams not being conti- 
nued uniformly straight at different depths, or by strata again 
passing laterally into each other, their tabular seams thus be- 
coming extinct, or by new tabular seams appearing in the 
course of their dip ; all of v/hich circumstances, on the supposi- 
tion that the direction or line of bearing manifested by such 
strata does not show equal variations, may be included in our 
ideas of collatei'al^ though not of parallel strata. The line of 
* On a future opportunity, probably, I shall give some reasons for supposing 
that this is the general mode by which the strata of England, usually named Jloeis], 
are connected with the rocks upon which they are found to repose. 
