TIDDEMAN : CARBONIFEROUS ROCKS IN UPPER AIRE-DALE. 487 
present the usual dip of the country, but following them outwards 
we find them riiiming into, and continuous with, the flanking beds. 
It is pretty obvious from their structure that the internal beds 
represent successive layers, limited in their area, of growths of 
organisms, and that they pass into steeply-shelving banks of similar 
debris lying on the flanks of the knoll at an angle of rest. The study 
of the fossils composing these respective beds quite confirms this idea. 
From these and other considerations, which would be too long 
to enter into here, there can be very little doubt that the mounds, 
or knoll-reefs, have been formed in a similar way to coral reefs, by 
growth upwards under favourable conditions of the animals of which 
they are composed, and by the piling up by waves, perhaps also in 
some places by winds, of the resulting debris. This has no doubt 
been going on upon a slowly sinking area, and it is a remarkable fact 
that none of these mounds so far have been found except on the 
sinking area on the downthrow side of the Craven Faults. 
It is evident from facts collected in this area that large portions 
of those reefs, if not all successively, have been exposed to the wash 
of the waves between wind and water, as is the case with coral-reefs. 
Breccias composed of fragments of limestone, mostly sharply angular, 
some more rounded, and others, less frequently, worn into pebbles, 
have been found abundantly in many places. In some cases the 
breccia forms part of the inner beds of the reef ; in others it is well 
developed in the flanking beds : and elsewhere we find beds of breccia 
formed on the sea bottom adjoining the reef, and inter-bedded with 
the lowest beds of shale accumulated on the sea bed from which the 
knoll has grown up. 
Here then we have good evidence of these white limestones 
having been formed in shallow water, so shallow that the breakers 
could play upon, break up, and re-arrange them on the shore platform 
above, or consign them to deep water below. 
Furthermore, some of the white limestones in certain places 
present phenomena which suggest that they have been formed, or 
rather re-constructed from calcareous debris, by wind-drifting, or 
have at any rate been consolidated in the open air, but as this matter 
is still under examination, I must postpone any further remarks on 
this part of my subject. 
