199 
Plate XV. Fig. 3, is the representation of a specimen of the Yorkshire 
entrochal marble, in which the organic remains are very beautifully 
disposed in relief on its surface. As I have already remarked, I am 
unable to discover any essential difference between the entrochi existing 
in the Yorkshire and in the Derbyshire marble. Those in the Yorkshire 
marble seem, however, to be generally smaller, and of a neater con- 
formation than those in the marble of Derbyshire ; but whether this 
proceeds from real difference of species cannot, perhaps, be determined 
from such specimens only as I have had the opportunity of seeing. 
The colour, in different specimens of the Derbyshire and Yorkshire 
marbles, varies much from a light to a dark browm. This specimen is of 
the latter hue. 
Plate XV. Fig. 2, represents a polished specimen of this marble, 
formed of the mineralized remains of separated columns of trochital 
vertebras. By attention to the different sections of these columns, a 
tolerably correct knowledge of their construction will be obtained ; 
remembering that the lighter parts are the remains of the original 
animal substance, and that the darker is the interposed crystalline 
matter. 
From the observations which I have been able to make on the 
remains of the encrinus in the limestone, or rather marble, of 
Wenlock Edge, in Shropshire, I am fully satisfied that it is a species 
different from both the lily encrinite and the cap encrinite of Derby- 
shire. My reasons for forming this conclusion I shall now offer to your 
consideration. 
The calcareous masses of the remains of encrini which are obtained 
from Wenlock, possess certain characters which immediately distin- 
guish them from such masses of entrochal marble as are obtained 
from any other part. The organic remains themselves are formed of 
calcareous matter, which being apparently very free from any ferrugi- 
nous impregnation, is nearly white; and hence the organic remains 
are, some of them, beautifully white and opaque ; whilst others, with 
