WILMORE : THE STRUCTURE OF SOME CRAVEN LIMESTONES. 167 
longitudinal river course which has produced the rather wide 
plain between the Worsaw mass and the Chatburn ridge. The 
river seems to have run behind the knoll mass, and to have 
flowed out, between it and the Worston mass, into the valley 
of Pendleside beds, and the course is marked at the outer end 
by a tiny stream now. The river has been captured by a trans- 
verse stream, and it now flows off across the strike through 
the lower part of Chatburn village. Worston knoll and the 
low hills of Bellman and Salt Hill are similarly accounted for. 
The more flaggy limestones and the limestones with shales 
have been more readily worn dowTi than the massive obscurely 
bedded crinoidal and shell debris higher in the series, and hence 
these latter beds now stand up as the knolls, the southern faces 
of these knolls being the well marked dip-slopes. The soft 
Pendleside shales immediately succeeding these limestone beds 
with their breccias have been cut down by the longitudinal 
stream drainages, and have thus intensified the knoll-like 
appearance. 
I do not deny that there may have been lenticular thicken- 
ings of these deposits, but it seems to me that Sir A. Geikie's 
explanation completely expresses the facts as regards deposition. 
He says, " The original reef-knolls described by Mr. Tiddeman 
from the Clitheroe district appeared to me to be due to the 
irregular aggregation of submarine organic debris in situ, though 
I could not detect any true reef structure."* 
The present appearances are due then, partly to the nature 
of the deposits, and partly to the ordinary agents of denudation 
acting differentially on the beds of varjang texture. 
It is noteworthy that the organic debris and breccia 
deposits with their rolled shells and other peculiarities are absent 
from the Barnoldswick-Thornton area. There the beds which 
lie immediately below the Pendleside shales and limestones 
are blue hmestones with abundant shale bands. The fauna 
of these blue Hmestones and shales is, however, as nearly that 
of the knoll deposits of Chatburn as could be expected. I hope 
to show in a subsequent paper that the crinoids, echinoids, 
* Text Book of Geology, Fourth Edition, vol. ii,, p. 1041. 
