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GEOLOGICAL MEMOIRS. 



the mass, the articulating surfaces of the joints are rendered freely 

 visible, and these are seen to be covered by a fine coating of ferruginous 

 ochre. The rays do not reach to the nutritive canal, and measure 

 from the rim only two millimetres in length ; they are from sixty-five 

 to seventy in number ; some of them, however, are split into two. The 

 nutritive canal is obtusely pentagonal, and is also filled with ferrugi- 

 nous ochre. Round about it, as far as the commencement of the 

 rays, the articulating surface is smooth. Consequently these joints 

 perfectly agree with Rhodocrinus verm, Goldfuss, tab. 60. fig. 3. 



Both in the nutritive canal of the broken column, and between the 

 articulating surfaces of some of the joints, fluor-spar is clearly recog- 

 nised as having penetrated into those cavities. The joints themselves 

 consist of calc-spar of a yellowish-brown colour, with a clearly rhom- 

 bohedral structure. 



The second stem-fragment shows three very evident joints, which 

 are circular like the former, but are only five millimetres in diameter, 

 and are equal in thickness. The denticulated line of suture of some 

 of the joints is more conspicuous on the surface than in the foregoing, 

 from which it does not differ in other respects. 



The third stem-fragment lies altogether in the crystalline portion 

 of the mass, and wants only a part of its outer surface. It has ten 

 grey-coloured joints, of equal size, connected together by denticulate 

 sutures ; their diameter is considerably less than that of the fore- 

 going- 



A fourth fragment consists of eight partly disunited joints, but 

 otherwise quite similar to those of the third fragment. They are all 

 enclosed in the granular portion of the specimen. 



A larger fragment lying on the boundary of the granular and cry- 

 stalline portions shows three joints, similar to those first described. 

 And in the granular portion, by close observation, we can detect also 

 small isolated joints more or less decomposed. 



From the above it appears that the specimen described is fluor-spar 

 metamorphosed from Mountain Limestone, in which the Crinoidal 

 fragments, by reason of their crystalline structure, successfully resisted 

 the influence of the fluoric acid ; and preserved their original form, 

 whilst the compact calcareous mass was so completely dissolved by 

 the fluoric acid rising from below, that it became converted into cry- 

 stalline fluor-spar. The earthy material, which is regularly distributed 

 throughout the granular fluor-spar, appears to consist of the argilla 

 and magnesia [? barytes and iron] originally present in the solid lime- 

 stone. The phsenomenon appears, therefore, to agree with that of 

 calamine long since known. [T. R. J.] 



On Recent Notices of the Nummulite Formation. 

 By C. Giebel. 



[Jahresbericht der naturw. Vereines in Halle, 1850, pp. 47-49.] 

 M. Giebel here gives a survey of the researches relating to the age 

 and geological position of the Nummulite Beds, made during the two 

 years previous to May, 1850. 



