Junction be- 
low Caldron 
Snout. 
172 Professor Sepawick on the 
that the unusual induration of this bed, has been produced by 
the agency of the trap*. (4) Under the indurated shale, appear 
a number of beds of dark encrinite limestone. The highest por- 
tion of them seems to have been slightly acted on, but the lower 
portion is in its ordinary unaltered state. The two preceding 
sections do not give any direct proof of the mechanical action 
of the trap. Its position on the west side of Forcegarth-hill, 
seems, however, to shew that its lower surface is not there parallel 
to the strata on which it rests. 
6. It appears from the section, (Pl. rx. Fig. 5.) that imme- 
diately below Caldron Snout, the trap is not parallel to the beds 
on which it rests. By this arrangement, it is brought into im- 
mediate contact with a succession of the inferior strata. 
Some of the phenomena produced by the junction, are exhi- 
bited in a natural section (See Pl. x. Fig. 1.) about 200 yards 
below Caldron Snout. The base of this section is formed by 
two beds of granular limestone, separated by a thin imdurated 
argillaceous bed of a light brown colour, and in texture resembling 
some yarieties of whet-slate. Over these comes a thin and very 
irregular argillaceous bed like the preceding, and the whole series 
is surmounted by an unconformable mass of columnar trap. It 
appears, by a comparison of specimens, that these argillaceous 
beds are exactly analogous to certain portions of the beds of slate- 
clay which abut against the trap dykes in Angleseat. The two 
beds of limestone are as granular as Parian marble, and do not 
contain a vestige of organic remains. Except where they are 
stained by impurities, they are of a dull white colour. The 
grains, which are highly crystalline, adhere very imperfectly to 
each other, so that projecting portions of the rock often shiver 
* 1 have been informed, that this indurated shale has been occasionally used for 
roofing-slate. 
+ See Professor Henslow’s Paper on Anglesea, Vol. I. p. 401. 
