THE JURASSIC DEPOSITS WHICH UNDERLIE LONDON. 759 
thickness as we proceed southwards. If we are right in referring 
the red and variegated beds at the bottom of the Richmond borehole 
to the Poikilitic, there will also be an additional and, at present, 
unknown thickness of strata of that age to be passed through. 
In the other deep borings within the London area, the Palzozoic 
ridge was struck at depths of 1000 ft. or less beneath Ordnance- 
datum line; but at Richmond, at a depth of nearly 1400 ft. below 
that level, the rocks of Paleozoic age do not seem to have been 
touched, and under any supposition the overlying rocks are 1220 
ft. thick. The considerations I have just stated lead one to fear 
that further to the south the distance of the Paleozoic ridge from 
the surface would be still greater. 
It must be remembered, however, that unequal elevation and 
denudation in pre-Cretaceous times might bring about a set of 
conditions which, if known, would ereatly tend to modify the above 
conclusions. Mr. Godwin-Austen suggested that old lines of 
disturbance often coincided with those of later date; and asa modern 
axis of disturbance is known to exist along the line of the North 
Downs, a coincident flexure of older date may have resulted in 
bringing the Paleozoic rocks nearer the surface. Hence Mr. Godwin- 
Austen has expressed himself in favour of a trial-boring for coal 
being made in the neighbourhood of the North Downs. 
Taking into account the probable thickening of the Oolitic rocks 
as we go southwards, as indicated by the Battle and the Richmond 
borings, and the possibility that Wealden strata may also be found 
to overlie these, as we approach the North Downs, it must be 
admitted that a very great amount of pre- -Cretaceous disturbance 
* and erosion would be required to place the Paleozoic rocks within 
moderate distance from the surface. 
Of course if the boring were commenced in any lower member 
of the Cretaceous series, there would be so much less rock to be 
passed through in the upper part of the boring. But in order to 
do this, it would be necessary to proceed southwards; and it is, to 
say the least, not improbable that the thickening of the Jurassic strata 
in passing southwards may more than counterbalance the removal 
of the Cretaceous beds by denudation. If the thick sandy beds of 
the normal Lower Greensand were met with, there would of course 
be a further, but probably not insuperable, difficulty encountered, 
that, namely, of sinking through very loose and pervious beds. 
On these grounds I cannot help fearing that the prospect of 
finding coal at workable depths under the southern part of the 
London Basin is rendered less hopeful in consequence of the results 
which have been obtained through the Richmond well. 
If the red rocks at Richmond belong to the Old Red Sandstone 
and not to the Poikilitic, it is still possible, bearing in mind the 
effects of the remarkable reversed faults in the old Paleozoic ridge, 
as proved by the researches of M. Gosselet, that Carboniferous strata 
might be found underneath them. The chance would, however, be 
probably regarded as too slender a one to encourage a prosecution 
of trials through such red rocks. 
3 EQ 
