214 TZ. V. Holmes—Geology of Blackheath and Greenwich. 
enlarged about that part at which water tended to enter, the material 
washed down, filling the chamber below and the lower part of the 
shaft. At last the cavity would become too large for stability, and 
the result would naturally be a subsidence at the surface taking the 
shape of that at pits Aand C. Hypothetical sections illustrating these 
changes were added to my remarks appended to the report of the 
Exploration Committee.? 
1 now turn to events at Blackheath of a much more recent date. 
During the last year or two enclosures were made at intervals on 
Blackheath from a spot close to the ‘‘ Hare and Billet’’ public-house, 
near Blackheath village, to the north-eastern corner of the heath close 
to the Charlton Road. They marked the positions of the shafts sunk 
along the course of the main drainage tunnel constructed in the Chalk 
beneath Blackheath. It soon became evident that the line taken by 
the tunnel, as indicated by the positions of two of these shafts, was 
such as to pass vertically beneath the site of the subsidence at A, 
which was, as already stated, precisely similar in size and shape to 
that at C, in which the Exploration Committee worked in 1881. 
Accordingly I wrote to Messrs. 8. Pearson & Son, Ltd., the 
contractors, mentioning my interest in subterranean Blackheath, and 
expressing a desire for information as to their experience of it. My 
request was most kindly granted, and I am much indebted to 
a member of the firm, Mr. B. C. Cass, for the following additions 
to our knowledge of the geology of Blackheath. 
Between a spot a few yards northward of the pond close to the 
‘Hare and Billet’? and another not far from the south-eastern corner 
of Greenwich Park there are five shafts along the line of the drainage 
tunnel. The shaft here called No. 1 is that near the ‘‘ Hare and 
Billet’; No. 2 is close to but eastward of Talbot Place; No. 3 is 
close to but on the northern side of the road between the south- 
western corner of Greenwich Park and Morden College; No. 4 is 
near but south of the Shooters Hill Road; and No. 5 is about 
70 yards southward of the south-eastern corner of Greenwich Park. 
The course of the tunnel is thus from south-west to north-east, and 
the portion of it which runs beneath the site of the subsidence at A is 
between shafts 3 and 4. As regards the depth at which water was 
met with during the sinking of these shafts, Mr. Cass gave me the 
following information :— 
Depth at which Height of surface 
Shafts. water was found. above ordnance datum. 
ify Jia feet. 
1 24 6 dee eis See 140 
2 3, © Site We: Save 150 
3 no water ... ane Bae 150 
4 a 0) ase RS ane 146 
5 34 @ 147 
He added that this water, which, percolating through the 
Blackheath Pebble Beds, is upheld by the more or less clayey beds 
1 These sections, reproduced from the report, may be seen in the ‘‘ Record of 
Excursions’ of the Geologists’ Association, pp. 5-8. They were introduced there 
to illustrate a very short report of an excursion to Charlton, Blackheath, and 
Lewisham conducted by Mr. J. Logan Lobley on April 30th, 1881, during which 
the subsidence at C was visited. The exploration was then in progress. 
