WILMORE : THE STRUCTURE OF SOME CRAVEN LIMESTONES. 33 
These grey, very fossiliferous limestones, which are usually 
very pure — many of them containing from 95 to 100 per cent, 
of CaCOg — are often put down as fairly deep-sea deposits, but 
from fairly extensive work among them I am confident they 
are shallow water beds. The shells, crinoid and coral fragments 
are debris matter, and much of it has been rolled into its place 
by the waves. Hence the indiscriminate mingling of the various 
classes of fossils and the sorting according to size — which is 
not at all uncommon. The rolled fossil shells, crinoids, and 
single corals also show beach conditions. 
The area of accumulation where these thick deposits were 
formed was singularly free from sedimentation of the ordinary 
type, though numerous shale partings at Clitheroe, Chatburn, 
and Downham show that such conditions were not far away, 
and that this clastic sedimentation sometimes prevailed over 
the shell-debris accumulation. The muddy habitat species 
invaded the region, as one would expect. 
It is noteworthy that, both here and in other parts of Craven 
where shell and crinoid debris is found, the delicate mat-like 
growths of Polyzoan colonies are often seen spreading indis- 
criminately over shells, coral, and crinoid fragments. I have 
seen these Polyzoa in the middle of some of the least definitely 
bedded of the knoll limestones spread quite evenly and in places 
parallel to that which would be taken as the dip ; this occurrence 
proves that these limestones are successive accumulations of 
organic debris, and that some at least of the want of bedding 
is due to secondary growth and deposit of calcite matter acting 
as a cement and causing some part of that structureless appear- 
ance which is characteristic of these hmestones. 
When we remember that these deposits are formed of 
shells and shell-fragments of various sizes, of crinoids, and of 
corals mixed together ; when we remember that the material 
of which they are composed is easily dissolved in natural waters 
and easily deposited again, we do not expect the same regularity 
of stratification that is seen in some other strata. I beHeve 
the rocks — both those in the massif and those forming the out- 
standing knolls — are in this respect much like the Hmestones 
c 
