65 
The diffusion of the red colour through this specimen requires some 
little attention. It extends through every part of the mass, and appears 
to have percolated through the external part of the coral into its internal 
substance ; in such a manner that no gross substance has entered ; the 
colouring matter appearing to have been here deposited from its solution. 
That the colour has not been derived from the coral itself, may safely 
be inferred : there appear, therefore, to be two modes by which this 
colour may have been yielded. Either the decomposed coral might 
have been imbedded in a matrix, of which the oxide of iron formed 
a part, and which, by the access of a fit menstruum, became capable 
of penetrating through every part of the coral : or both the coral 
and the surrounding matrix might derive their colour from the influx 
of the coloured fluid derived from some other source. In either case, 
it appears evident that this diffusion of the colouring matter, and 
its introduction into the mass, were previous to the perfecting of the 
lapidifying process. 
On subjecting this marble to the action of diluted nitrous acid, its 
decomposition took place very speedily. A considerable quantity of 
carbonic acid gas was separated, the calcareous part was dissolved, 
and a red substance, an oxide of iron, gradually sank to the bottom. 
Whilst the decomposition was proceeding, a substance was detected, 
whose presence, at least in so obvious a state, was not expected. As 
the separation of the other parts took place, ragged, flocculent pieces 
of apparently a membranous substance were left, adhering to those 
parts where the coralline substance had been observable. These, on 
the least agitation of the fluid, were seen to wave to and fro, and on 
the motion being increased fell off, and soon reached the bottom of 
the vessel from the weight of the solid matters which were attached 
to them. 
In the specimen of marble figured at Plate VI. Fig. 1, from Kil- 
kenny, the remains of a coral of this kind, but of a larger species, 
are very evident. The ground of the marble is of a deep black, but 
the part of the marble possessed by the coral is of a very light grey. 
VOL. II. K 
