240 
POPULAR SCIENCE REVIEW. 
than in the Ardennes and the Mendips, where it has exercised 
its maximum elevatory force. In that case the coal trough 
in this intermediate area would be less compressed and more 
expanded, and we might consequently look to find larger coal- 
basins than those of either Somerset or Liege. 
The strata on the south side of the Liege coal-field rise 
abruptly against highly inclined and faulted Devonian rocks, 
and on the north side they rise, at a less angle, beneath 
Cretaceous or Tertiary strata ; and to the westward the great 
palaeozoic axis of the Ardennes, consisting of Silurian and 
Devonian rocks, Mountain Limestone, and Coal Measures, passes 
westward under the Chalk of the north of France, and has 
been followed underground as far as Calais, where it lies at a 
a depth of 1,032 ft. ; while in the direction of Boulogne the 
old rocks keep nearer the surface, crop out from beneath the 
chalk downs surrounding the Boulonnais, and disappear near 
the channel under an unconformable series of Jurassic and 
Wealden strata. 
We may, I think, look for a prolongation of this old 
palaeozoic surface of highly inclined, contorted, and faulted 
rocks at no great depth under the same Cretaceous and Tertiary 
area of the south-east of England. For, although the old 
palaeozoic surface descends rapidly from 200 ft. above the sea- 
level in the Boulonnais to 1 ,032 ft. below it at Calais, it rises 
at Ostend 47 ft. higher than at Calais, and, crossing the 
Channel, it is found at Harwich within a few feet of the same 
depth as at Calais, from which it is eighty miles distant in a 
northerly direction. Passing westward, we find the palaeozoic 
rocks under London, 105 miles distant from, and 102 feet 
higher than under Calais, and 106 feet higher than at Harwich. 
Allowing for irregularities of the old surface as evinced by the 
well at Crossness, near Plumstead, which was still in the Orault 
at a depth of 944 feet, or some 14 feet below the level of the 
palaeozoic rocks at Kentish Town, we may still consider that 
in the area between these three points, and other parts on the 
same range of the south-east of England, the palaeozoic rocks 
will probably be found not to be more than from 1,000 to 
1,200 ft. beneath the sea-level. 
Projecting the line another 100 miles westward, we reach the 
neighbourhood of Bath and Frome, where the coal measures are 
(as before mentioned) lost, at a depth of about 500 feet, beneath 
Liassic and Jurassic strata. In the intermediate area between 
that place and London no trial-pits and no wells have been 
carried to a depth of anything like 1 ,000 feet beneath the sea- 
level. The deepest well with which I am acquainted is one 
near Chobham, in Surrey, through tertiary strata and chalk to 
a depth of about 800 feet, or 600 feet beneath the sea-level. 
