An Unconformity in the Carboniferous. 161 
below the hammer—contains cavities filled with sandstone, or with 
sandstone and shale. The latter are similar to, but generally smaller 
than, that shown in Fig. 2.° One near the shovel has been partly 
picked out with a white line, but the others do not contrast 
sufficiently with the enclosing limestone to show up in the photo- 
graph. Those filled with sandstone alone are difficult enough to 
delimit on the ground, as the sandstone has a calcareous cement 
and is firmly welded to the similarly-weathering limestone that 
encloses it. 
Pl. II (b) shows a wider extent of the junction of limestone and 
Grit, the distance from A to H being 50-60 yards. The base of the 
Trias (above and to the left of B) is shown by a broken black line. 
The surface of separation of Grit from limestone is marked, by con- 
tinuous black lines, only where it is clear in the photograph; between 
the Grit-filled hollows C and £ it was too complicated to be traced 
readily. For one thing undisturbed limestone has an awkward trick 
of poking up amid Grit where least expected. The masses in this 
position may be presumed to be remnants, isolated laterally by 
confluent Grit-filled hollows, somewhat similar to the top (B) of 
the limestone between the Grit-filled hollows A and C, which appears 
to be surrounded by Grit. Doubtless B is, or has been, continuous 
with the limestone below, and the strip of Grit, apparently below it, 
is either banked against it or fills a channel crossing it. In some cases, 
however, as in that of undisturbed limestone at D, the boundary 
with the Grit is most irregular, and no adjacent limestone is exposed. 
Conversely, as in the limestone enclosing the channel shown in 
Pl. I (a), Grit appears repeatedly in the limestone below the black 
line, filling vertical “‘ pipes” and irregular cavities. Generally the 
communicating passage with the main mass of Grit above 
is not to be seen, but one definite “pipe”, shown in Fig. 1, 
is continuous therewith. The overlying Grit is seen on the 
right, and the bottom of the “pipe” is 10 feet below. 
The contents (sandstone and shale) have evidently remained 
undisturbed since their first introduction, as sand and mud, and 
consolidation. The 4 in. sandstone, shown in detail at the bottom 
of the figure, curves sharply in conformity with the steeply-sloping 
surface of the limestone-wall and with the shale filling the bottom 
of the “ pipe”’, but is now quite hard. 
A large, irregular cavity (Fig. 2), 6 yards in length, filled with 
sandstone and shale, of which the form was more than usually clear, 
was seen in the quarry-face opposite that shown in Pl. II (b). The 
sandstone occurs partly as a horizontal wedge, about 6 feet thick 
at the larger end, partly as thin lamine interbedded with the shales. 
At one place small carbon-lined moulds suggest that plant- 
fragments have been washed in with the sand, now represented 
by the sandstone. On the right the cavity is prolonged vertically 
downward as a funnel-shaped shale-filled “ pipe’’. This was cleared 
for 34 feet below the sandstone-wedge without being bottomed. 
VOL. LVIII.—NO. Iv. 11 
