235 
THE BLACKHEATH SUBSIDENCES. 
By T. Y. HOLMES. 
M ANY readers of the Popular Science Review have doubtless 
. heard of the strange subsidences that have appeared on 
the surface of Blackheath during the last three years, and have 
attracted so much attention from the suddenness of their 
appearance, and the mystery surrounding their origin. For 
when it is remembered that these subsidences suddenly dis- 
closed themselves in the midst of a gravel plateau, every foot 
of the surface of which is liable to he tested by cricket, golf 
and football players, schoolboys and holiday-makers, it is 
evident that nowhere could they have been more unlooked for 
and alarming. 
Having been a member of the executive branch of the 
committee formed for the purpose of investigating one of these 
remarkable holes, and the exploration being now finished, 
I am enabled to give some account of our labours and their 
results. In addition, I shall review the evidence bearing on 
the subject, and point out what seems to me to be the most 
probable conclusion derivable from it. Perhaps the best plan 
will be to begin with a sketch of the geology of the neighbour- 
hood, a clear understanding of which is absolutely necessary, 
before giving the details of our workings. The archaeological 
evidence need not be taken into consideration till the geological 
evidence has first been fully weighed. 
The voyager from London to Woolwich cannot fail to 
notice the range of wooded heights on which Greenwich 
Observatory stands, which contrasts so much with the low 
ground bordering the Thames in other directions. This range 
is flat-topped, and is bounded on the east by the valley of the 
Darent, and on the west by that of the Pavensbourne ; Black- 
heath occupies the promontory at its western end. At the base 
of this wooded range lies the Chalk, which is well exposed in 
