THE BLACKHEATH SUBSIDENCES. 
243 
be to give a general account of tlie archaeological evidence 
bearing on the matter, and then to discuss its applicability to 
the case before us. 
Artificial shafts in the chalk occur in great numbers in parts 
of Norfolk, Suffolk, Kent, and other counties where chalk 
abounds. They naturally divide themselves into two groups : 
those made for the purpose of obtaining chalk and flint (mainly 
the latter), of which ‘ Grime’s Graves,’ in Norfolk, about three 
miles N.E. of Brandon, furnish by far the best known ex- 
amples : and those made as places of security, and of warmth 
in winter, of which the ‘ Danes’ Holes ’ of Crayford and other 
places in Kent, near the south bank of the Thames, are the 
most noteworthy instances. 
The ancient pits known as Grime’s Graves have been fully 
described by the Rev. Canon Greenwell, and from his paper on 
the 4 Opening of Grime’s Graves,’ * I will make a few brief ex- 
tracts, sufficient to show their general character, and refer those 
desirous of more details to the paper itself. 
The pits are about 254 in number, and are generally about 
25 feet apart, covering a space from 20 to 21 acres in extent. 
They are circular, and vary in diameter from 20 to 65 feet. 
They have all been filled up to within about 4 feet of the sur- 
face. The pit selected for examination was about 28 feet in 
diameter at the mouth, and gradually narrowed to a width of 
12 feet at the bottom, which was 39 feet below the surface. It 
was cut through a deposit of dark yellow sand, 13 feet thick, 
which there overlies the Chalk. At the depth of 19^ feet from 
the top of the Chalk was a stratum of flint of better quality than 
any nearer the surface. This is called by the present workers 
— for in this neighbourhood the manufacture of gun-flints still 
goes on — the ‘ wall-stone,’ and is used for building walls, ■)* 
though not hard enough for gun-flints. At a depth of 7\ feet 
below the wall-stone, or 39 feet from the surface, a second bed 
of flint exists of much better quality, which was, and is now, 
used for gun-flints. It is probable that the ancient workings 
were established in this place on account of these qualities in 
the flint. At the bottom of the shaft this bed of flint, known 
now as the ‘ floor-stone,’ was worked out as far as the shaft ex- 
tended, and then galleries were driven out in various directions 
upon the level of the bed of flint, the overlying chalk being 
removed to a height of 3 to 5 feet. The galleries vary in width 
from 4 to 7 feet, and the flint was worked out beyond their 
sides as far as was practicable without causing the roof to give 
way. These galleries probably connect all the shafts. There 
were no steps cut in the sides of the pit, and the workmen either 
* Journ. Ethnological Sue. Jan. 1871. 
t See Mr. S. B. J. Skertchly’s Geological Survey Memoir on Gan 1 lints. 
