COAL-MEASURES IN THE SOUTH-EAST OF ENGLAND. 237 
the cause of similar folds in the same rocks of Somerset and 
Wales, were continued along the whole line of disturbance, and 
that the preservation of portions of the same great supple- 
mentary coal trough is to he looked for underground in the in- 
termediate area, just as they exist above ground in the proved 
area. The intermediate subordinate barriers dividing the coal- 
basins can, I conceive, in no way permanently affect the great 
major disturbance, by which the presence of the coal measures is 
ruled. 
Admitting, however, that the coal measures were originally 
present, the question has been mooted whether they have been 
removed by subsequent denudation. 
It has been urged that the Coal Measures become unproduc- 
tive, and thin out under the Chalk, as they range from Valen- 
ciennes towards Calais, and, therefore, that the coal-trough or 
basin ends there. It is perfectly true that the Coal Measures 
do thin out between Bethune and Calais, but not in the sense 
of their dying out owing to their deposition near the edge of a <= 
basin. In that case, each seam, each stratum would gradually 
become thinner and disappear, but such is not the fact. None 
of the beds of the Belgian coal-field are thick ; the average 
does not exceed 2^ft. At Valenciennes it is the same ; whereas 
M. Burat states that the mean thickness of the beds actually 
increases westward of Bethune to more than 2Jft. With 
respect, also, to the extreme end of this basin, the lower beds 
there brought up correspond with the bottom beds of the 
Hainaut basin, where the lower 650 feet consist altogether of 
unproductive measures. The thinning-out is, in fact, due to 
denundation, just as the Bristol coal-field thins out at Cromhall 
to resume in the Forest of Dean, or the coal-field of Liege 
thins out at Nameche to resume at Namur in the great fields of 
Charleroi and Mons. 
The deterioration of the coal in the small coal-field of Hard- 
inghen, near Boulogne, has also been adduced against the 
occurrence of workable coal in south-eastern England ; but Mr. 
Grodwin-Austen has shown that this Hardinghen coal-field is 
one of those small local developments of coal-bearing strata 
intercalated in the Mountain Limestone, and is of older date 
than the great Belgian coal-field. It has, therefore, no bearing 
on this part of the question. 
Another objection, to which much weight has been attached, 
is, that as the coal-field of Bath and Bristol forms an inde- 
pendent basin, cut off both on the east and on the west by ridges 
of Millstone Grit and Mountain Limestone, we have there 
reached the eastern boundary of the coal measures. It is 
probable that such a bounding ridge does exist, though, as the 
edge of the basin is there covered by secondary rocks, there is 
