SILURIAN, DEVONIAN, AND CARBONIFEROUS ROCKS NEAR LONDON. 287 
coal measures of the Somerset basin maintain their full develop- 
ment to the edge of the basin and are then cut off by denuda- 
tion and not brought to an end by thinning out. They form part 
of a more extended mass of which we have more than one 
fragment, while on the west another portion exists in the Welsh 
basin, and another in the newly-discovered small basin of the 
Severn Valley, and there is no reason why on the east the same 
disposition should not 'prevail .” * These far-seeing views as to the 
probable physical history of the extended deeply-seated area be- 
tween Bath and Frome and the German Ocean are being slowly, 
but I believe surely, verified, and bear entirely upon the researches 
now being carried on, and upon the palseogeographical distribution 
of rocks and life over an immense underground tract, and which 
here and there, by means of the boring-rod, are being tested, and 
those theoretical views of Mr. Godwin-Austen and Professor 
Prestwich confirmed. 
Although, however, at present no true Coal-measures have 
been touched or proved along the valley of the Thames, or 
their extension known to take place from Therouanne, still 
the above views, although speculative, have the same value 
as when first propounded ; for although the Devonian rocks have 
been proved at Tottenham Court Road, and Turnford, six miles 
south of Ware, it in no way invalidates or does away with the 
possibility that south of that area or even west of London the 
Coal-measures may occur. The failure of the sub-Wealden 
exploration, intended to prove the presence of these older rocks 
below the Wealden area, leaves the question still open as to the 
correctness of the views propounded by Mr. Austen with relation 
to the extension of the Boulonnais and other rocks. Speaking 
of the axis of Artois, Mr. Austen says,f 66 that it is continued 
across our area by the range of the North Downs, and those of 
Hants, and that on the north limit of this ridge the beds dip 
suddenly and rapidly; hence a line of fractures extending from 
near Arras to the east end of the Boulonnais and from the north- 
west point of the Wealden denudation to the Valley of Devizes.” 
This relative depression on the north has preserved the Num- 
mulitic series (Lower Tertiary), just as along the Franco -Belgian 
line the depression was the cause of the preservation of the great 
coal trough. Applying this consideration to the structure of 
our area, from Kent into Somerset, we may feel sure that a like 
arrangement of the older strata was from the Valley of the 
Thames into the Kennet ; along this line the coal measures may 
be reasonably supposed to have been preserved 4 
* Vide Popular Science Review, vol. xi. p. 237-240. 1872. 
t 11 Quarterly Journ. Geolog. Soc.” vol. xii. p. 62. 
t Vide pi. VII., fig. 8. 
