216 T. V. Holmes—Geology of Blackheath and Greenwich. 
if they were non-existent in that shaft; for the word ‘ballast’ being 
used for gravel in that section only, suggested a different reporter of 
the strata in that case. In reply Mr. Cass remarked :—‘“‘ In No. 4 
pit we did not come across any of the shell deposits as we did in 
Nos. 2 and 8. No. 4 was very free from shells, only very few being 
found in the sands.”” And as regards the spot between shafts 3 and 4 
at which the tunnel passed beneath the hole formed by subsidence A 
on April 12th, 1878, Mr. Cass informed me that at a depth of about 
120 feet the chalk there was found to be all broken up and mixed 
with material of various kinds which had fallen from above, 
I have already alluded to the deep shaft ending in a chamber in the 
Chalk discovered at Eltham. Early in the year 1878 there was 
a leakage in the water-supply at Eltham Park, the seat of 
Mr. T. Jackson, about three miles from Blackheath. A disused 
brick drain, being opened up, was found to end at the top of a shaft 
4 feet in diameter and 140 feet deep, at the base of which was 
a chamber in the Chalk, the extreme dimensions of which were 
40 by 68 feet and the height 93 feet. The lowest 22 feet of 
the shaft were cut through the Chalk, and it was lined throughout 
with courses of brick and chalk. Mr. Flinders Petrie read a paper 
describing it at a meeting of the Royal Archeological Institute on 
March Ist, 1878, from which these details are taken. At some period 
much later than that of its original construction, the chamber had 
been utilised as a cesspool, for a period, Mr. Flinders Petrie thinks, of 
‘‘at least a century, perhaps two or three centuries.” As to the 
objects of its makers, he finds no suggested explanation satisfactory. 
On that point I weuld only add that it seems evident that it must 
have been made for the sake of the chamber, and not for that of the 
material extracted therefrom, and consequently that it belongs to the 
denehole class. 
The beds traversed by the shaft at this Eltham pit are the same as 
those at Blackheath. The Thanet Sand was 52 feet thick at Eltham, 
the Woolwich Beds 26 ft. 3in., and the Blackheath Beds 37 ft. 9 in. ; 
the top of the Chalk being 116 feet below the surface there, instead of 
101 ft. 6in. to 103 feet, as found near the sites of the Blackheath 
subsidences A and ©. And while the nature of the beds composing 
Blackheath would be unusually easy to recognise in primitive times, 
as they are more or less visible close by, on the slopes of the Lower 
Tertiary escarpment, both northward and westward, there are no 
similar helps to observation at Eltham. 
We have seen that the exploration of the subsidence at C, in 1881, - 
showed that the strata vertically beneath were much shattered and 
mixed together, greasy clay being obtained at a depth of 84 ft. 6in., 
where the Thanet Sand exists in undisturbed ground. And the course 
of the recent tunnel beneath the subsidence at A indicated that the 
Chalk there at a greater depth was broken up and mixed with other 
material from above. In addition we know that the appearances pre- 
sented by both these subsidences at the surface were practically 
identical, their vertical sides suggesting shafts, while the expansion, 
beginning at a depth of about 18 feet from the surface, would be the 
natural result of the action of the water (met with at a depth of 
