144
SUBTERRANEAN GEOLOGY OF SOUTH-EASTERN ENGLAND.
measures might be found there below the Carboniferous Limestone
and Devonian rocks. Accordingly instead of stopping on touching
Devonian strata the borers continued their work. Devonian rocks
had been met with at a depth of 131 metres, and geological antici-
pations were verified by the finding of Carboniferous Limestone at a
depth of 168.30 metres. Another borehole was begun a little north-
ward, as the beds were rising in that direction, and there, under
Cretaceous rocks, Carboniferous Limestone was reached at a depth of
148 metres, and Coal-measures were found at 170 metres. Another
boring was then made still further north, and there Coal-measures
were reached immediately below the Tourtia, a bed of Cretaceous
age. The explanation here, as at Namur, appeared to be that beds
of pre-coal-measure age enclosed a fold of coal-bearing strata, the
older rocks being thrust over the newer by a crumpling force exerting
immense pressure from south to north, and causing the reversal of
the beds. This, as in the other case, has been accompanied by the
production of a fault hading to the south, up the plane of which the
older rocks have been thrust.
Fig. 1.—Section through the Basins of Namur and Dinant (Gosselet). From the Proc.
Geol. Association.
H. Coal-measures. d. Upper and Middle Devonian. c. Carboniferous Limestone.
R. Lower Devonian (Rhenan). s. Silurian and Cambrian.
Prof. Prestwich adds that W. of Auchy-au-Bois, the fold of
Coal-measures appears to thin away, so that the coal field there,
though once continuous with that of Hardinghen in the Boulonais,
now forms a separate basin.
Thus, if we examine the geological structure of Southern Belgium
and Northern France, we see that (as Godwin Austen pointed out),
the evidence from that quarter alone would make it highly probable
that this crumpled ridge of Palaeozoic rocks still exists on our side of
the Straits of Dover below the Secondary rocks forming the surface,
and, in all likelihood, at a moderate depth.
Let us now go westward of this part of England and see if beyond