BRITISH ASSOCIATION MEETINa. 
27 
durin!» the opening of the cavern ; but, on looking narrowly at the beds of 
limestone in the progress of the workings, it was found that a thin seam of 
purple culcareous "slate" was interposed between the beds of limestone, at 
about the same parallel as that in whieh the caverns were met with. On fur- 
tlicr investigation, it was discovered that alternations of this piu-ple " slate" 
with the limestone were not unfrequent, but the lamina; of slate were, in most 
cases, so intimately blended with tlie limestone-beds, as to form really a solid 
mass of compact rock ; and on lookmg into the structure of the more evident 
layers of the " slate," it was ascertained that in some parts they were much 
more calcareous tiian in others, and that small portions of limestone, having 
similar physical characters to those of the surrounding rock, were interspersed 
at varying intervals. In other places the layers were in a state of decomposi- 
tion, red and reddish white clay being formed as its result ; and on tracing a 
layer of this kind through the side of a cavern laid open during the workings, 
it was seen that portions of it were so disintegrated as to be easily pulled from 
their position, the seam being, in its most solid portions, composed merely of 
layers of limestone-fragments with interposed clay and red sand — the whole, 
apparently, kept in place by the accidental infiltration of calcareous matter. 
Here, then, were facts that might enable me to account for the clay found in 
the caverns, and afford a means through whieh the beds of limestone may have 
been caused to separate from each otlier. Agam, it was discovered that some 
of the hollows in the adjoining limestone were stained with a black earthy sub- 
stance, found, on analysis, to be composed of the peroxides of iron and man- 
ganese, these having evidently proceeded from the decomposition of a variety 
of dolomite very generally present in this limestone — not exhibiting, however, 
any definite mode of deposit in it, but passing through its beds m the most 
irregular manner. From these phenomena, it appeared reasonable to conclude 
that the decomposition of the " slate" in the layers, through the combined 
agency of water and carbonic acid, had opened a communication with the 
external air to the above-named ii-regular masses of dolomite (the unchanged 
limestone-fragments of the " slate" serving to keep the beds from close contact 
with each other), and that in this way the carbonates of iron and manganese 
contained in them had been converted into peroxides, and the evolved carbonic 
acid proceeding from their decomposition, combining with the remaining consti- 
tuents of the dolomite, had formed bicarbonates, readily removeable by the 
agency of percolating water. In this way it is possible, not merely to account 
for the formation of the caverns, and a means of access to them, but at the 
same time to discover what are the causes still in operation which give rise to 
' the production of stalactite, and occasion the irregular dolomization of the lime- 
stone, it being evident that the percolating waters, charged with bicarbonates 
of linie, magnesia, &e., may, by a loss of carbonic acid, deposit insoluble car- 
i bonate of lime in the form of stalactite, and becoming by this means richer in 
! bicarbonate of magnesia, act chemically on the neighbouring limestone, convert- 
j ing it into dolomite. 
I To test the correctness of these views, a very careful examination of the clay 
below the bones was instituted : it was extremely tenacious, and of a dark 
reddish-brown colour ; patches of red clay were visible in some places, and in 
\ other parts of the mass distinct yeUow and black layers were apparent, and 
i nodules, or, more strictly speaking, irregular masses of impure ochry red iron- 
[ ore, together with black, rounded fragments, evidently arismg from the decom- 
j position of a dolomite similar to that before alluded to — for in the larger frag- 
\ ments this rock was distinctly visible on fracture, and in one or two instances, 
I in which the masses were larger than usual, a brown zone was obsei'vable 
i between the black external coating and the central nearly unaltered dolomite ; 
large and small masses of the common limestone-rock of the quarry were also 
