234 
rOPULAR SCIENCE REVIEW. 
of the subject by the Royal Coal Commission,* enables us now 
to investigate the physical problems with still greater certainty. 
It is evident from what we have already said that the age 
and position of the surface rocks afford no criterion of the 
thickness of the strata intervening between that surface and 
the palaeozoic rocks underlying the Tertiary and Secondary 
strata of the south of England*; while it is also clear that the 
relation of the secondary and of the palaeozoic group of rocks 
to one another is perfectly independent, and that the latter 
must be viewed entirely on their own internal evidence, apart 
from the bearing of the newer rocks which cover them uncon- 
formably. 
A glance at the geological map of Europe will show that 
the Belgian coal-field is but part of a series of great coal- 
fields ranging from Westphalia to the north of France. These 
coal-fields are deep, long, and narrow, and their longer axes 
succeed one to another on the same line of strike.* Omit- 
ting a few small unimportant coal-basins, the most easterly of 
the great coal-fields is known as that of the Ruhr, the second 
as that of Aix-la-Chapelle, the third as that of Liege, and the 
fourth as that of Hainaut and Valenciennes. In all these 
districts the Coal Measures are tilted up or faulted on the 
south against the Mountain Limestone or the Devonian rocks, 
or pass northward under Cretaceous and Tertiary strata, beneath 
which they are prolonged until thrown out by other undula- 
tions of the older rocks. The width, north and south, of these 
coal-fields is always small compared to their length. Thus the 
coal-field of Liege is only 3 to 8 miles wide, whereas it has a 
length of 45 miles. So the exposed coal-field of Hainaut, from 
Aamur to beyond Charleroi, is 33 miles long ; it then passes 
under the Cretaceous and Tertiary strata, and is prolonged, with 
a few small exposures, underground, by Mons to Valenciennes. 
The length of this other underground portion of the coal-field is 
32 miles, making a total of 65 miles, with a width near Namur 
* Vol. of Evidence taken before Committee D, and Report to that 
Committee u on the Probabilities of finding Coal in tbe South of England ” 
by the writer ; Royal Commission on Coal Supply, 1871. Free use is made 
in this paper of this report and also of the writer’s anniversary address to 
the Geological Society for 1872. 
t These are given generally in the map, PI. LXXXV., the main features of 
which are copied from Dumont’s Geological Map of Europe. To them are 
added the ascertained range of the Coal Measures under the Chalk of the 
North of France and their probable range under the South of England. 
To this I have added a series of hypothetical sections along the line' of the 
coal trough and across it, showing the possible disposition of the Coal Mea- 
sures and the thickness of the overlying strata. 
