312 
Chalk near Théronanne, would probably be found to 
make their appearance again near Calais, and to be 
prolonged beneath the Chalk and Tertiary beds along 
a line parallel to, if not coincident with, that of the North 
Downs, and thence away towards the Bristol and Somer- 
setshire Coalfield. 
In the Report of the Coal Commission, published in 
1871, Prof. Prestwich has very ably argued the whole 
question, and brought forward a large amount of new 
evidence bearing upon it. 
That geologists were right in their prediction of the 
existence of a ridge of Palxozoic rocks (the Axis of 
Artois), extending under the metropolitan area, has now 
been abundantly proved by boring operations. The 
strata of the Bristol and Somerset Coalfield have been 
traced and worked for a distance of about six miles under 
the overlying younger strata. That these overlying strata 
‘tend to thin away as they are followed towards the east 
has been proved by Prof. Hull and other geologists who 
have studied the Trias, Lias, and Oolites of the Midland 
district ; and Prof. Prestwich has shown from a boring 
made at Oxford that the whole of the Lias and Oolites, 
which to the westward are several thousands of feet thick, 
beneath that city, are reduced in thickness to 420 feet. 
At Burford, in Oxfordshire, Coal-measure strata have 
actually been proved to exist at a depth of 1184 feet from 
the surface, and at Northampton at 830 feet. At Harwich, 
Carboniferous strata were found at a depth of 1026 feet ; 
at Ostend, Paleozoic rocks were found at 975 feet ; and 
at Vilvorde, near Brussels, at about 600 feet. These 
facts serve to show that a great attenuation of the Meso- 
zoic strata takes place, as they were followed towards the 
south-east, and that the Palzozoic rocks are brought by so 
much nearer to the surface. 
To the eastward, where the strata of the Belgian coal- 
field are found to be covered by overlapping younger 
_ strata, the productive measures have been followed by 
the enterprising French mining engineers, by means of 
pits sunk through the tertiaries and chalk, and in this 
way valuable coal supplies have been obtained along 
nearly the whole of the line from Mons and Charleroi to 
Lillers. At Hardinghen, between Calais and Boulogne, 
coal-measures are, in consequence of upheaval and denu- 
dation, exposed at the surface, while near the former town, 
strata of Carboniferous age have been found at a depth of 
1138 feet. 
The interesting experimental boring put down at Battle 
in Sussex, in order to prove the depth of the oolites be- 
neath the Wealden, resulted in a very interesting disco- 
very. It was found that in this district the Jurassic strata 
are of considerable thickness, and that it is therefore 
hopeless to attempt to reach the Paleozoic axis in that 
part of the Wealden area. 
Five deep borings have however demonstrated the very 
moderate depth at which the Paleozoic rocks lie in the 
Metropolitan district. At Tottenham Court Road the 
Paleozoic ridge was found at a depth of 1066 feet; at 
Kentish Town at 1114 feet ; at Turnford, near Cheshunt, 
at 940; at Ware at 796 feet; and at Crossness, near 
Erith, at 1008 feet. The exact age of the beds reached 
at Kentish Town and Crossness is somewhat doubtful, 
but at Tottenham Court Road and at Turnford the 
Upper Devonian was found, and at Ware the Wenlock 
“NATURE 
shales of the Upper Silurian. We are indebted to. Mr. 
Etheridge for a careful study of these borings, and for the — 
determination of the numerous fossils obtained from 
them. 
Another interesting fact demonstrated by these borings 
is that the strata lie at very high angles, the dip found 
at Tottenham Court Road being 36°, and that at Ware” 
a 
30°. 
The evidence obtained from these borings proves that — 
| 
the rocks forming the old Paleozoic ridge are bent into a’ 
series of east and west folds, and among these folds it is 
highly probable that Coal-measure strata will be found. 
As to the point at which a boring might be put down 
with the greatest chance of success, several different 
opinions exist. 
Prof. Prestwich thinks that a point in the southern 
suburbs of London, such as Sydenham or Croydon, is 
well worthy of being selected as the site for a new trial, 
and he points out that, even if coal were not found, the 
Lower Greensand might be met with, and this would in all 
probability be found to afford such an abundant supply 
of excellent water that the money expended in the in- 
vestigation would not be thrown away. 
Mr. Godwin-Austen, believing that a probable corre- 
spondence will be found to exist between the modern and 
ancient lines of disturbance, suggests some point near 
the North Downs, which is the axis of a great post- 
Cretaceous flexure, as the most hopeful one. 
Some authorities have favoured the idea that it will be 
wise to avoid the task of sinking through the chalk, by 
commencing south of the North Downs, while others, 
foreseeing some difficulties in putting down borings and 
shafts through the loose running sands of the Folkestone 
beds, are in favour of a renewed attempt in more northern 
points of the Wealden district. But in face of the facts 
revealed by the Battle boring and the known thickness of 
the Wealden, it may well be doubted if it would be 
advisable to commence so far away from the proved 
position of the Palzeozoic axis. 
The coal-basins, if they exist on this Palzozoic ridge, 
are probably long and narrow in form, like those of Bel- 
gium and Northern France, having their longer axes 
directed from east to west. We now know that the 
Paleozoic ridge lies at depths varying from 800 to 1200 
feet below the surface in the London district. 
profitably worked in many pits in this country more than 
2000 feet deep, there is no reason why the coal, if dis- 
covered, should not be mined under London. We are 
now, therefore, in a position to state what are the require- 
ments fora systematic search for coal under this city, 
and the conditions under which that search must be 
made. 
This question, which is one of such paramount import- 
ance to the people of London, would probably be completely 
set at rest, if a series of borings were put down along a 
line running from Hertford on the north to Redhill on the 
south, a distance of less than forty miles. Considering 
| the probable narrowness of the coalfields (that of Belgium 
averages less than four miles in width) the borings ought 
to be only afew miles apart, and thus at least ten or 
twelve borings with a probable average depth of 1000 feet 
would be necessary. But, of these required borings, four 
have already been executed, those namely at Ware, 
As coal is 
ee 
