33 



The appearance which this fossil bears might convey the notion of 

 its having suffered by compression. But this is rendered highly im- 

 probable, by the circumstance of coral obtaining such a degree of 

 hardness, at its first formation by the animal, as would effectually 

 oppose any attempt to change its form, except by fracture. That many 

 substances, originally hard and unyielding, may, during the changes 

 they undergo in the progress of their mineralization, become soft and 

 compressible, is very probable; but there is nothing in the appearance 

 of this fossil to warrant the suspicion of its having been thus affected. 

 The mode in which the perpendicular lamina terminate serves also to 

 determine the question: the line in which they end, in the centre, being 

 exactly appropriated to that form which the fossil bears ; and which 

 therefore may be concluded to have been its original and natural form. 

 It is also deserving of particular notice, that the parietes of this coral- 

 lite are remarkably thick and dense. 



In the fossil, represented Plate IV. Fig. 7? a turbinated madrepore, 

 the perpendicular lamellae of which are rendered visible by the de- 

 composition and removal of its external coat, is seen blended in the 

 same mass with the remains of the encrinus. In Plate III. Fig. 4, a 

 corallite of this species is seen attached to the mass of chain coral, 

 exemplifying the proverb, Noscitur ex sociis, three different species of 

 animal remains, whose originals are unknown to us, being thus found 

 associated. 



A complete and rare specimen of marble from Blankenberg, formed 

 by this species of madrepore, is shewn, Plate IV. Fig. 14. Not only 

 is the form of the disk well preserved, but even the internal structure 

 of the madrepore may be here perfectly made out. 



The next species of madrepore which demands our attention is the 

 shirt-button madrepore (?nadrepora porpita. Linn.). This is a flattish 

 orbicular body, smooth on the inferior surface, being marked there 

 only by very minute circular lines and perpendicular striae, and 

 having, on its disk, a star, somewhat convex towards the edge, but 



VOL. II. F 



