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have given a diagram showing a similar thinning out and over- 
lapping of the strata from south to north in the north of 
France, and a like unconformable in dependence of the secondary 
Fig. 2. 
and of the palaeozoic series, only there the older strata come to 
the surface, which they do not in south-eastern England : — 
Fig. 3. 
Westward of this line of diagram in France, the palaeozoic 
rocks sink deeper, and are altogether covered by secondary and 
tertiary strata ; and while at Lille the chalk is found to repose 
on the mountain limestone , at Valenciennes it reposes on coal 
measures . These latter are the prolongation of the great 
Belgian coal-field, which ranges from Liege westward to and 
beyond Mons. 
It is about two centuries ago that the Belgian coal-basin was 
found to pass beneath the newer -formations westwards in the 
direction of France, where the Coal Measures were supposed 
to be lost under these Cretaceous and Tertiary strata. It 
occurred, however, to some more far-seeing men that they 
might possibly be recovered, and, after various trials, their 
search was attended with success, the strike of the coal mea- 
sures hit upon, and valuable collieries established at Anzin and 
Aniche, in the neighbourhood of Valenciennes. This en- 
couraged further search, and the coal measures have been 
gradually followed in a westerly direction under the chalk to 
within thirty miles of Calais, and at that town a boring for 
water, made by M. Mulot in 1842, proved the presence of 
carboniferous strata (but not the coal measures) under the 
