THE BLACKHEATH SUBSIDENCES. 
239 
Road, about three-quarters of a mile E.N.E. of the hole, the 
Chalk was found to be 109 feet below the surface,* the height 
of the surface being about 150 feet. The surface at the hole 
is about 132 feet above Ordnance datum, w r hich would give 
91 feet as the probable depth of the Chalk there, granting it 
to be at the same level in the two places, which is probably 
very nearly the case. About a mile W. of the hole, at Black- 
heath Hili, the top of the Chalk appears to be about 50 feet 
above Ordnance datum, which would give about 80 or 82 feet 
at the hole. The Thanet Sand, which directly overlies the 
Chalk, was 55 ft. 10 in. at the Brewery at Greenwich Hospital 
(now Haval College), but at Loampit Hill, Lewisham, is only 
about 40 feet thick. The Woolwich beds, at Blackheath, 
judging from the sections now to be seen at Westcombe Park, 
and from those seen by Prof. Prestwich in the cutting east of 
Blackheath Station, are a little over 20 feet thick. Greenwich 
Hospital Brewery gives 23 \ feet.f The thickness of the 
pebble beds which form the surface of Blackheath is, of course, 
variable. 
In Westcombe Park the Woolwich beds are not fully seen, 
but the shell beds are about 5 ft. 6 in. thick, and below them 
is sandy clay containing nodules of sandy ironstone. It may 
be interesting to compare the section at Greenwich Hospital 
Brewery, with that seen by Mr. Prestwich east of Blackheath 
Railway Station.* 
Woolwich 
"beds. 
Blackheath Railway Cutting. 
Blackheath pebble beds , 10 to 12 feet. 
f Brownish sand ...... 
Broken-up shells in light-coloured clay, with 
pebbles 
Brok en-up shells in greenish-grev clay 
Light green sandy clays, mottled red and grey . 
Light greenish sands with a few pebbles (bottom 
l bed) 
Feet. 
2 
4 [ 
2 
Shelly 
beds. 
Thanet Sand 
21 
Greenwich Hospital Brewery. 
Blackheath •pebble beds. 
f Black sand 4 10 
j Blue clay . . . . . . 0 8 ( Shelly 
Woolwich] Shelly rock 4 0 ( beds. 
beds. 1 Red clay 0 0 
j White sand ...... 40 
1 Green sand and pebbles .... 40 
Thanet Sand 23 6 
* Whitaker, Geol. Bond. Basin , p. 457. t lb. p. 405. f lb. p. 124. 
