33 
The appearance which this fossil bears might convey the notion of 
its having suffered by compression. But this is rendei'ed 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 laminae 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. 17. 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 (madrepora 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 
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