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THE QUESTION OF WORKABLE
Now, as the detritus derived from the higher land regions
together with the vegetable matter of the Coal accumulated along
the margins of the earlier continental regions of elevation to a
thickness in the British area of over 15,000 feet (and equal to the
aggregate of maximum thicknesses of all the British Secondary and
Tertiary formations), certain mechanical results must have followed.
The enormous additional burden thus imposed upon these areas of
deposition would tend to depress them. Such a force acting verti-
cally downwards would be resolved partly into lateral thrusts tending
(1) to pinch-up in places the Carboniferous limestone floor of the
sea at greater distance from the land, giving rise to new and minor
axes of elevation ; (2) to increase the elevation of the land-regions
from which the detrital material had been derived followed or
accompanied by increased degradation of their materials. There is
evidence of the latter having actually occurred, in the conglomerates
and sandstones of earlier Permian strata (known as the Rothlie-
gendes), some of which are shore deposits, while others of vast
thicknesses, as in Thuringia and in Devonshire, bear evidence (as
shown in my recent papers on the Devon Red Rocks in the
"Journal of the Geological Society") of having accumulated on the
flanks of great mountain regions of older land. In parts of
Germany and Austria these Rothliegende strata even contain work-
able Coal-seams, a fact which testifies to their land origin ; in other
cases the Coal-Measures proper are worked beneath them, as they
are in Notts and elsewhere beneath the red strata of the Trias,
which in many cases overlap both Permian strata and Coal-
Measures. But we cannot go here into details.
Further movements of the crust occurred during that long
period in which the sandstones, pebble-beds, and marls of the Trias
(one of the most puzzling of all geological systems) were deposited,
by which large marine basins were formed, the outline of which we
can, in the light of the accumulated evidence furnished by geology,
trace as far back as the Jurassic period. Such were, in the
European area, the Anglo-Gallic Basin, in which the secondary
strata of the south east of Britain and the north of France were
deposited ; the North Sea Basin (continuous with the former)
covering all of what is now North Germany and Denmark ; the
Aquitanian Basin of the South of France; the Helveto-Germanic
Basin, which, as a narrow sea extending over Northern Switzerland
and Southern Bavaria, connected the Pannonian Sea of the great