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POPULAR SCIENCE REVIEW. 
traverses the Boulonnais and is probably prolonged under our 
Wealden area, is one of the many central ones, or the lateral 
one immediately flanking the coal trough, is uncertain. 
Any attempt made to solve this great problem must be 
hailed with satisfaction, and we therefore look upon the trial 
about to be made by the Sub-Wealden Exploration Committee 
as a most important step in this direction. The site selected 
for the experiment near Battle is on the line of centre of the 
Weald, where the lowest Wealden beds come to the surface, 
and it is no doubt on or near the line of continuation of the 
axis of the Boulonnais. We may, therefore, there expect to 
meet with a prolongation of that axis consisting either of the 
Mountain Limestone, with the subordinate coal strata of Hard- 
inghen, or the Devonian Limestone and grits. Had it been 
merely a trial for coal another site might have been selected, 
but the object the Committee has in view is one purely scien- 
tific, to determine the thickness of the Wealden and underlying 
secondary strata, and the depth, nature and position of the under- 
lying palaeozoic rocks ; and it has been suggested and planned in 
honour of the next meeting of the British Association at Brighton 
— of which meeting it will be a worthy memorial. It is not by 
one experiment, however, but rather by several, that the im- 
portant question of the line of the great trough of productive 
Coal Measures will be determined. This experiment will pro- 
bably be but one of a series. We hope to learn by it the 
direction of the strike of the older palaeozoic rocks, and then 
judge of the bearing and probably position of the coal trough 
in relation thereto. Ho insurmountable difficulties present 
themselves. The starting-point is the lowest in the series of 
the known rocks of the south-east of England, and if it should 
prove to be on the crest of the prolonged ridge of the Boulonnais, 
the other secondary strata may be of no great thickness. But 
this is entirely a matter of experiment. We know not what 
may be the thickness of the remainder of the Wealden, and if 
Beneath that we find the Purbeck and Portland beds, the Kim- 
meridge clay, and some of the Oolitic series in place, as we do 
in the Boulonnais, we know not what thickness they may attain.* 
* The thickness of the strata may vary within the following limits : 
Probable Minimum Probable Maximum 
Feet. Feet. 
Asburnham Beds 
. 50 
. 50 
Unproved Wealden . 
. 100 
. 300 
Purbeck and Portland 
. 30 
. 50 
Kimmeridge Clay 
. 300 
. 800 
Oxford Clay 
. 200 
. 400 
Oolites 
. 50 
. 100 
730 1700 
Paleozoic strata to be proved beneath these beds. 
