a AP 2 ie 
a ew. 
i - ie, OEE 
ihe 
- ' 
494 GEOTECTONIC (STRUCTURAL) GEOLOGY. [Boox IV. 
which the coarse shingle of the dolomitic conglomerate (b b) accu- 
mulated; that the latter, traced away from its shore-line, passes on 
the same plane into red marl (c), and that during a gradual sub- 
sidence, the clays and limestones of the Lias (d) crept over the 
depressed shore-line. He likewise called attention to the important 
fact that, in such cases, a continuous zone of conglomerate may 
belong to many successive horizons. In Fig. 212 a section is given 
from one of the islands in the south-west of England, round which 
the Trias and Lias were deposited. Denudation has stripped off a 
portion of the overlying red marls. If the rest of the section to the 
left of the dotted line d d were removed, there would remain a 
continuous mass of conglomerate, which, in default of other evidence 
to the contrary, would be regarded as one bed laid down upon the 
sloping surface of limestone, instead of what it really is, a series of _ 
shore gravels piled upon each other, and belonging to a consecutive 
series of deposits. 
Mere difference of lithological character, even within a limited 
geographical space, does not necessarily mean diversity of age. At 
the present time coarse shingle may be formed along the beach at 





Fic, 212.—SEcTION OF PART OF THE FLANK OF THE MeEnpIP Huis (B.), 
showing the Carboniferous Limestone (a a) overlaid by dolomitic conglomerate (b )) 
and that by red marls (c). 
the same time that the finest mud is being laid down on the same 
sea-bottom further from land. The existing differences of character — 
between the deposits of the shore and of the opener sea would no 
doubt continue to be maintained, with slight geographical displace- 
ments, even if the whole area were undergoing subsidence, so that 
a thick group of littoral beds might gather in one tract and of © 
deeper-water acccumulations at another. Among the formations 
of former geological periods the same conditions of deposit appear 
sometimes to have continued for enormous periods. The thick Car- 
boniferous Limestone of western Europe evidently accumulated 
during a slow subsidence, when the same conditions of clear water 
with abundant growth of crinoids, corals, &c., continued for a period 
yast enough to admit of the gradual growth of thousands of feet of 
calcareous matter. Traced northwards into Scotland this massive 
limestone is gradually replaced by sandstones, shales, ironstones, 
and coal-seams. These strata prove that the deeper and clearer 
water of Belgium, central England, and Ireland passed northwards 
into muddy flats and sandy shoals, which at one time were overspread 
with coal-growths, and at another, owing to more rapid enbaidaest 
were depressed beneath the clearer sea which brought with it the 
