170 



dently from the introduction of a considerable proportion of carbo- 

 nate or oxide of iron into their composition. Those which are ob- 

 tained from JBlackenburg, are generally of a deeper colour than those 

 which we find in England. 



The nature of these bodies was, for a long time, entirely unknown. 

 In 1751 Mr. Lieberoth, of Hettstedt, published an essay on the ori- 

 gin of these substances in the Hamburgh Magazine, in which he en- 

 deavoured to prove, that these cylindrical bodies were the remains 

 of some totally unknown animals, which, like the earth- worm, had the 

 power of contracting and of elongating themselves. This opinion was 

 .opposed by Mr. Lehman, who contended, that these stones owed their 

 peculiar forms to the rays of the Caput Medusae, impregnated with 

 iron. M. Vogel hazarded a conjecture, that these forms might arise 

 from particular species of strombites. A satisfactory explanation of 

 the origin of these bodies was first given by Mr. Schulze, who attri* 

 buted their formation to the introduction and deposition of an 

 ochrous matter in the cavities of entrochi. 



Whoever will take the pains to examine the internal structure, and 

 the cavities existing in the vertebral column of the encrinite, and will 

 also attentively view the screw-stone, cannot but perceive, how exactly 

 the cavities of the one correspond with the projecting parts of the 

 other ; and how certain it is, that the screw-stone is the cast of the 

 internal part of this column. 



But little difficulty will, I believe, occur in explaining the manner 

 in which this cast is formed. These columns, being immersed in 

 water, holding earthy particles, merely in a state of diffusion, 

 would gradually have every cavity filled with the earth which would 

 be hence deposited ; and would also become surrounded with an 

 earthy mass, which, having gradually acquired a pulpy state, would, 

 as evaporation proceeded, obtain, with that which had filled all 

 the cavities of the column, a stony hardness : thus we should 

 have the cakareous animal remains completely filled with, and im- 



