OF RHYMNEY AND PEN-Y-LAN, CARDIFF. 491 
ment necessary, ceases just before we reach Lanishen station, and 
the railroad is once more carried through a “ cutting.” Deposits of 
gravel, sand, and clay are first exposed; these attain a thickness of 
as much as 30 feet, and contain here and there large subangular 
boulders of limestone and grit; one of these boulders, evidently 
derived from the Mountain Limestone, measured 3X33 x2 feet. At . 
the base of these gravels the Old Red Sandstone is exposed at 
Lanishen station; it there consists of a loose conglomerate which 
dips from $.W. to N.E. atalowangle. Further on, red shales with 
calcareous nodules occur beneath the gravel at the signal-box past 
the fifth mile marked on the section. These beds, also of Old Red 
age, dip from N. toS. at an angle of about 11°. The half mile 
between Lanishen and the signal-box, which is covered by gravels, 
would thus appear to conceal the axis of a synclinal fold. 
The southward dip of the Old Red beds, which from this point 
are continuously exposed, is maintained for half a mile further 
north ; it is then replaced by a dip in the opposite direction, the beds 
(sandstones, conglomerates, and marls with thin bands of cornstone) 
rolling over in an anticlinal curve which is beautifully revealed in 
the banks of the railway-cutting. The dip is now northward, and 
does not again change within the limits of our section, the Carboni- 
ferous shales and limestone coming on conformably with a dip in 
the same direction, and at a distance of 1188 yards from the place 
where the axial ridge of our last anticlinal occurs. Over this dis- 
tance the average dip of the Old Red Sandstone may be taken as 
about 30°, which gives us 1782 feet as the approximate thickness 
of the Old Red which lies between the axis of our anticlinal and 
the base of the Carboniferous series. If only the Silurian had been 
brought up by the anticlinal, we should now know the thickness of 
the Old Red in our district ; as it is, our knowledge so far amounts 
to no more than the certainty that this thickness cannot be less 
than 1782 feet. Let us, however, make an approximate calculation 
of how much ought to be added to this minimum thickness in order 
to obtain the total thickness. The beds south of the anticlinal axis 
appear to dip at a less average angle than those to the north of it, 
so that we may expect to find them extending over a greater dis- 
tance than those which they repeat. We return now to the ground 
beneath which our supposed synclinal lies; and as the position of 
its axis is not known, we may assume it to lie midway between the 
signal-box, where the beds dip to 8., and Lanishen station, where 
they dip to N. This midway point is distant 1496 yards from the 
axis of the Old Red anticlinal; we eliminate this distance from our 
section, then, as belonging to beds which have already been measured. 
The dip of the beds between the axis of the synclinal and that of 
the anticlinal is, as we said, less than 30°; it would not do, there- 
fore, to measure off another 1496 yards to the south as repre- 
senting the beds repeated on the south side of the synclinal; it 
will be fairer to take the 1188 yards which the same thickness of 
beds dipping at 30° would cover for that purpose. Having now 
allowed for the repetition of the strata on the south side of the anti- 
