61 
that some similar and prevailing change affected the sea 
bottom at each particular epoch, and brought about the condi- 
tions necessary to form those singular accumulations of animal 
remains, which are appropriately termed ‘bone beds.’ With 
the exception of the Rheetic bone bed, all the rest are simply 
an aggregation of broken and disconnected fragments of 
fish, * chiefly Cestracionts, (sharks,) usually forming a very 
thin stratum, seldom exceeding a few inches in thickness, 
and probably of limited extent. These fish remains are 
usually associated with the marine shells of the period, 
though not in any great profusion. The Rheetic bone bed 
differs from these in the mixture of rolled and broken frag- 
ments of Saurians, with fish remains, and abundant copro- 
lites of both, and also in its greater extent and thickness. 
For this reason this is the only one which might perhaps be 
useful as a manure, as it contains abundance of calcium 
phosphate, the others consisting for the most part of remains 
of fish, which, however interesting to the Icthyologist, would 
be unavailable for this purpose. Unfortunately the Lias 
bone bed is highly charged with pyrites, (sulphide of iron) 
which sometimes permeates the bones, and gives it an in- 
creased hardness and metallic lustre; although there are 
some layers where it is very soft and crumbly, and occasion- 
ally numerous bones, teeth, &c., are scattered in sandstones 
and limestones without pyrites, where they might be turned 
to some account; with this view I sent some specimens to 
the Great Exhibition, in 1851. Now it is well-known that 
sulphuric acid is obtained from the pyrites in the London 
clay, possibly this Rheetic pyrites might also be used in the 
same way, and if this could be done and the animal remains 
picked out and made into a bone manure, the economical 
* The Ludlow ‘bone bed’ is an exception, as numerous fragmentary remains of 
Crustacea, (Ceratiocaris,) are associated with those of fish. 
