240 
POPULAR SCIENCE REVIEW. 
In Westcombe Park, water comes out along tbe line of 
outcrop of the shelly beds ; and Mr. Chapman, station-master 
at Blackheath, informed me that water, evidently from the 
same source, affords a supply for the railway station. The 
water is that which, falling on the permeable pebble beds in 
the form of rain, is upheld by the impermeable clay of the 
shell beds below. The shell beds were cut through in making 
Blackheath tunnel, and the water held up by them keeps the 
tunnel constantly wet. There can be no reasonable doubt that 
the water found at a depth of 34 feet in the hole, and which 
afterwards rose to 33 ft. 1 in. after rains, was water from the 
base of the pebble beds, and indicated the close proximity of the 
shell beds below. In the Yale of Health, Messrs. Jackson and 
Bond found that water was met with at a depth of from 12 to 
14 feet. How as the average height of the surface at the Yale 
of Health must be about 18 or 19 feet below that of the surface 
at the explored hole, more than 400 yards N.E. of it, we have 
herein evidence that the water in both places is from the same 
source, and that the shell beds lie at each spot at very nearly 
the same level. 
The geological evidence already given shows decisively 
that the various spoonfuls of material brought up from the 
hole cannot represent the nature of the beds existing below the 
surface of Blackheath in undisturbed ground. And we have 
also learned from it how exceedingly improbable is the existence 
of any faults or disturbances of the strata there. For while we 
have more evidence than is usually available in areas of similar 
size tending towards the last-mentioned view, it is apparent, 
from the sections given of the constituents of the various beds, 
that the only clayey beds belong to the Woolwich series and 
are about 12 or 13 feet thick at the utmost, whereas, judging 
from the contents of the spoon, clayey beds exist of a thickness 
of more than 30 feet. In what way, then, can this apparent 
thickness of clay be accounted for ? 
The sticky nature of clay, and the small quantity of material 
brought up may have had some influence in this result, but will 
not, I think, fully account for it. We have now, in fact, ar- 
rived at a point at which it becomes necessary to consider the 
two views which may be taken as to the origin of these Black- 
heath subsidences, and their respective probabilities. The first, 
which may be called tbe geological view, supposes them to 
have arisen from the breaking in of the roof of caverns in the 
Chalk formed simply by the action of water, which, percolating 
through the overlying tertiary beds, has dissolved away the 
Chalk in the manner so often seen in the ‘ sandpipes ’ of chalk- 
pits and railway cuttings. The second, or archaeological view, 
is that these subsidences are the result of the action of water on 
