SILURIAN, DEVONIAN, AND CARBONIFEROUS ROCKS NEAR LONDON. 285 
“ whether, if so, the coal measures were likely to occur under 
such condition of depth with respect to the overlying formation 
as would render them available to us.”* 
It was not the question of the Coal-measures only being 
present ; on theoretical grounds any other still older sedimentary 
rocks down to the lowest Cambrian may occur — continuous, 
either as old land from northern or eastern Europe, or as an 
easterly prolongation or extension of our north and south Welsh 
Cambrian or Silurian rocks, rolling away beneath the central, 
eastern, and southern counties; the floor, indeed, on which 
stand unconformably all the newer or secondary and tertiary 
series in their varied features as we now see them.f 
It must be borne in mind that in tracing out the physical 
outlines of western Europe during early times, or its early 
physiography, Mr. Austen included under the term Carboni- 
ferous those rocks, or conditions, whether terrestrial, fresh-water, 
or marine, from the Marwood and Pilton beds of the Upper 
Devonian to the top of the Coal-measures or the Upper Palseozoic 
group. His middle group comprised two series, being equivalent 
to the Upper Silurian and Devonian, and his Lower Palaeozoic 
group embraced all the marine sedimentary strata up to the 
Lower Silurian inclusive ; it is important to define the classifica- 
tion then used by Mr. Austen, and also in subsequent research 
and literature. 
Mr. Godwin- Austen :£ showed that the coal measures which 
thin away under the chalk near Therouanne probably set in 
again near Calais, and are prolonged (beneath the Tertiary and 
Chalk strata) in the line of the Thames Valley parallel with 
the North Downs, and continue thence under the valley of the 
Kennet into or towards the Bath and Bristol coal area. On 
theoretical grounds, carefully thought out, he concluded that 
the Coal-measures of much of England, France, and Belgium 
were probably once continuous, and that the present coalfields 
were merely fragments of one great original deposit which he 
inferred had been broken up in two directions, but prior to the 
deposition of the now overlying secondary rocks. This line of 
disturbance trended generally in an east and west direction, and 
part of it formed the anticlinal of the Ardennes, by which the 
Belgian coalfield had been brought to the surface; and the 
Mendip Hills with the Somerset coalfield are also on that same 
* “ Quarterly Joum. Geolog. Soc.” vol. xii. loc. cit., and vide Plate VII. 
fig. 8 map showing the continuity and probable extension of the Belgian 
coal-measures under the Straits of Dover and the Wealden area, etc., and on 
to the Mendip Hills and South Wales, (Copied from Professor Prestwich’s 
paper, Pop. Sci. Review, vol. xi.). 
t Vide Section 4, pi. VII. 
X “ Quarterly Journ. Geol. Soc.” vol. xii. 1875. 
