64 
internal structure is shewn to illustrate the figures which proceed from 
this kind of coral, in several of the marbles, found in dilferent parts of 
the British empire. 
In a fragment of a madreporite of this kind, of a large size, being 
two inches in diameter, from Coalbrook Dale, the external surface is 
so marked by longitudinal striae and transverse ridges, as to give it 
very much the resemblance of a jointed reed : and it is so filled with 
lapideous matter as not only to have obtained the compactness and 
weight of stone ; but to have had nearly all its interstices filled up, 
and its characteristic star obliterated. Its substance appears to be 
penetrated also with bitumen, some of which still remains on its surface, 
and is sufficiently soft to receive easily a mark from the pressure of the 
finger. 
Plate VI. Fig. 3, represents a specimen of marble, nearly formed of 
a small corallite of this class. This marble, which I lament the not 
^ being able to determine where it was obtained, is of a brownish red 
cnlpur ; being much darker in its interstitial parts than in the corallites 
themselves, and is susceptible of a good polish. 
The madrepore which has entered into the formation of this marble, 
appears to have been of the smaller species ; the branches being about 
the size of a goose-quill. From the cutting of the marble, various 
^ sections of the madrepore, in different directions are obtained, by 
which its internal structure is rendered very evident. In the trans- 
verse sections, the radii formed by tbe perpendicular lamellae or plates 
are seen uniting in the centre, and making the madreporean star. In 
some of the longitudinal sections ; in those, in which the coral has 
been divided. Immediately upon one of these longitudinal plates, a 
plain unfigured substance appears, the same as when the division is 
near to the external or conical surface of the coral ; but in those, in 
which the section has been made between these plates, there the 
sections of the horizontal plates are seen intersecting the perpendi- 
cular ones. 
