65 



The diffusion of the red colour through this specimen requires some 

 little attention. It extends through every part of the mass, and ap- 

 pears to have percolated through the external part of the coral into its 

 internal substance ; in such a manner that no gross substance has en- 

 tered ; the colouring matter appearing to have been here deposited 

 from its solution. That the colour has not been derived from the 

 coral itsejf, may safely be inferred : there appear therefore to be two 

 modes by which this colour may have been yielded. Either the de- 

 composed 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 men- 

 struum 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 per- 

 fecting 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, fiocculent 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 



