34 WILMORE : THE STRUCTURE OF SOME CRAVEN LIMESTONES. 
of Derbyshire, of North Yorkshire, and of other localities where 
there is no question of knoll formation. 
The nature and origin of these limestones is very closely 
mixed up with the problem of the origin of the Reef-knolls 
incidentally referred to already. The views of Mr. Tiddeman 
are so well known that they need no recapitulation, and the 
criticisms and suggestions of Prof. Marr, Mr. Dakyns, Dr. Hind, 
and others will be well known to members of this Association. 
I offer some remarks and suggestions here and in a later part 
of this paper. 
There are four well-marked knolls in the Clitheroe-Downham 
district and one semi-knoll. They may be called, proceeding 
from east to west, Twiston Knoll, Sykes Knoll, Gerna, Worsaw 
(the highest of all), and Crow Hill. They stand out as Penin- 
sulas or islands in the lowland, whih is mapped as " shales with 
limestones " by the Survey officers. Worsaw reaches 700 feet, 
that is about 300 feet above the level of the lowland plain. It 
is noteworthy that there is every gradation between the slight 
cape of the great limestone massif— as at Worston (Crow Hill) — 
through the well-marked Sykes peninsula to the " island " of 
Gerna. 
The general dip of the limestones here is synchronous with 
that of the shales in the district, which lie between the massif 
and the masses of grits in the Pendle range — the rocks of the 
massif itself have the same general dip. The dips in the knolls 
themselves sometimes show something of the quaquaversal — 
this is especially marked in the case of Gerna — and thus the 
strike lines become elliptical or circular. 
The dips are perfectly well marked and, as already men- 
tioned, in one part of Worsaw Hill the limestone becomes par- 
ticularly well bedded. 
It is noteworthy that no similar masses occur on the north- 
western side, and that the organic breccia-like character of the 
limestone has gradually given place to the well-bedded more 
fossile limestone formed of fine organic debris, and which is the 
normal limestone in the greater part of the area treated of in 
this paper. The breccia-like character is still maintained 
towards the middle of the massif and here the scar and mound- 
