﻿TRANSLATIONS AND NOTICES 



OF 



GEOLOGICAL MEMOIRS. 



On Crinoidal Remains in Fluor-Spar. By A. L. Slack. 



[Jahresbericht naturw. Verein. Halle, 1850, pp. 77-79.] 



Lately, in breaking a specimen of Derbyshire fluor-spar in my col- 

 lection, which was remarkable for its irregularity of shape, I was 

 astonished at finding some column-joints of Rhodocrinus verus, Goldf. 

 As is well known, there is a very fine specimen of a Crinoidal stem 

 enclosed in fluor-spar, also from Derbyshire, in Werner's collection 

 at Freiberg, and regarded of great importance by Werner and all 

 mineralogists. Immediately on perceiving the crinoidal joints in the 

 freshly broken fragments, I felt the impossibility of assenting to 

 Werner's explanation of the pheenomenon ; and I proceed to describe 

 my specimen in detail, and the more so as a third of the sort is not 

 known to exist*. 



The mass was a footf long, and half a foot wide, by three inches 

 high. For half its height it consists of fluor-spar crystals in cubes 

 of from three-quarters to one inch in size ; the colour is dark, almost 

 indigo-blue, and translucent ; the surface bluish-grey and opake. 

 The lower half is composed of small-grained, laminose fluor-spar of 

 the same colour, in which are enclosed light-yellowish and brownish 

 earthy substances, forming nearly an eighth part of the whole. The 

 lower face is also covered with small blue crystals of fluor-spar, and 

 a few scalenohedral crystals of calc-spar. There is a sharp horizontal 

 plane of separation passing through the length of the mass between 

 the crystalline half and the lower small-grained half. 



From its shape, the specimen broke into several pieces some inches 

 in size. On the limits of the granular and the crystalline fluor-spar, 

 and projecting into the latter, I immediately perceived two stem-frag- 

 ments, which I recognised as Rhodocrinus verus. The one consists 

 of eight connected joints, five of which lie in the one, and three in 

 the other fragment. These circular joints have a diameter of nine 

 millimetres, and a variable thickness of one to two millimetres. The 

 slightly convex surfaces of the sides appear in the thicker joints 

 to be covered with isolated warts, at least such a wart is clearly dis- 

 cernible on the otherwise crystalline laminated surface. From the 

 circumstance of the stem-fragments being broken with the fracture of 



* [Such specimens have been met with not unfrequently at Castleton and Mat- 

 lock, Derbyshire. — Transl. ] 

 f German measure. 



VOL. VII. PART II. L 



