64 



internal structure is shewn to illustrate the figures which proceed from 

 this kind of coral, in several of the marbles, found in different parts 

 of the British empire. 



In a fragment of a madreporite of this kind, of a large size, being 

 two inches in diameter, from Coal brook 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 sur- 

 face, 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 

 colour;, being much darker in its interstitial parts than in the coral- 

 lites 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 the perpendicular lamella? 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. 



