84 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. II. 



column, arms, and tentacula ; of the plates of the receptacle ; 

 anji of the peduncle, or process of attachment by which 

 the animal was permanently fixed to the rock. The peduncle 

 is in some species flat and expanded, like that of the Gor- 

 gonice; in others, it consists of long jointed processes. These 

 several parts are commonly found detached, and intermingled 

 with detritus in the strata; throughout extensive beds of 

 encrinital marble, vestiges of the receptacle are but seldom 

 discoverable. In some localities the skeletons are pre- 

 served entire, and spread out on the surface of the layers 

 of shale, clay, or limestone, as if the animals had been enve- 

 loped by the soft deposit when alive in their native seas, 

 as is the case in many of the beautiful specimens before us. 



These remarks will convey a general idea of the nature of 

 the beings whose remains are scattered through certain rocks 

 in such inconceivable quantities ; for, much as the columns 

 may differ in form, the ossicula in their markings, and the 

 plates of the receptacle in their configuration and ornament, 

 the same type of structure prevails throughout the family. 



These durable parts of the animal fabric occur in immense 

 quantities in the ancient secondary deposits ; and in many 

 parts of England, and of northern Europe and America, 

 entire mountain-chains are chiefly composed of the bones and 

 detritus of Crinoidece, belonging to numerous extinct species 

 and genera. 



Screw or Pulley-stones. Upper Shelf F. The circular, 

 or pentagonal channel formed by the united ossicula of the 

 column, has given rise to the curious fossils called, in Derby- 

 shire, Screw, or Pulley-stones, which are flint casts of these 

 cavities. These bodies occur in the chert, which is interstra- 

 tified with the mountain limestone ; the siliceous matter, 

 when fluid, having filled up the channels, and invested the 

 calcareous stems : the latter have since been dissolved, and 

 consequently solid cylinders of flint, resembling a pulley, 

 alone remain ; the masses of chert are often impressed with the 

 ornamented articulating surfaces of the ossicula, or trochites. 

 These fossils are sometimes mineralized by galena, or sulphuret 

 of lead, as in the specimens in this cabinet. 



In the quarries on Middeton Moor, near Cromford, Derby- 

 shire, where extensive beds of limestone composed of crinoideal 

 remains are worked for chimney-pieces, and other ornamental 



