VAUGHAX : THE KXOLL REGION OF CLITHEROE, ETC. 
47 
FIRST THEORY— The KNOLLS. 
The characters of knolls are now well understood by their study 
in many formations and in many localities ; especially is this the 
case for the Carboniferous (Waulsortian) knolls in the Dinant Area 
of Belgium, where examples are perfectly dissected by the gorge of the 
Meuse. 
At the time, however, at which Mr. Tiddeman was working, such 
knolls as those of Clitheroe were practically unknown to English geolog- 
ists, and their proximity to the great Craven Faults suggested a common 
tectonic cause. Mr. Tiddeman maintained however, that the knolls 
were nothing more than discrete heaps on the sea floor which rose above 
the surrounding sediments (if any) to near the water surface in the form 
of reefs — " knoll-reefs 
It will be sufficient to point out here the fundamental characters 
of knolls which Mr. Tiddeman succeeded in unravelling. 
(i) The brecciated and calcite-veined nature of the rock. 
(ii) The persistance of the " dip of the country ' through a dissected 
knoll as seen in the Clitheroe quarries — however much it may be 
obscured by the nature of the knoll material. 
(iii) The final roofing-over of a knoll by a dome-like layer of beds 
caused by the return of continuous deposition over the whole floor. 
Owing to this phenomenon, the outer layer ot a knoll usually exhibits 
that qua-qua-versal dip upon which Mr. Tiddeman insisted and wiiich 
is so well brought-out by the detailed mapping. 
In the case of the Clitheroe knolls, the qua-qua-versal dip of the 
outermost beds is well shown at the eastern end of Warsaw, [Examples 
of this phenomenon are splendidly exhibited in the Belgian knolls 
near Waulsort, where they are cut through by the Meuse]. 
(iv) The deep-water character of the phase ; this he deduces 
from the abnormal thickness of the deposits (see below). 
We now know that the knoll phase always lies outside — that is. 
* Altliough the Congress Report, cited above, speaks twice of 
Coral Reefs, this is an error of translation ; ]Mr, Tiddeman held that 
a knoll was a mere accumulatio7i and not a i-ecif coiifitna'l. 
