ORIGIN OF CHARACTERS OF OPHITES AND RELATED ROCKS. 15 



fig. 1 b) : it is necessary to mention that they have no definite 

 form as in the case of crystals. 



In the third) the fibres are comparatively stout, appearing 

 like cylindrical aciculse ; they closely adhere to one another, and 

 are usually of a glistening white colour (Plate IX. fig. 1 c). 



In the fourth, the aciculse, still retaining their colour, are 

 more or less separated, and the spaces between them are occupied 

 with calcite. Immersed for a short time in a weak solution of 

 hydrochloric acid, a layer of chrysotile in this stage has its 

 calcite dissolved out, leaving the aciculae separated thus be- 

 coming pectinated (Plate IX. fig. 1 d). 



It is now necessary to mention that the aciculse under the two 

 last forms have been taken for organic structures casts of fine 

 tubuli penetrating the calcite in immediate contact with and 

 covering the spheroids and layers of serpentine. Hence they 

 have been identified with the fine tubulation characteristic of the 

 " nummuline wall " of the Nummuline group of Foraminifera. 



Specimens are common showing all the varieties of chry- 

 sotile graduating into one another satisfactorily demonstrating 

 that they are simply modifications of one and the same divi- 

 sional structure. 



But it will be necessary to show how the difference between 

 the second and third stages in the modifications of chrysotile 

 has been produced, also the greater difference which distin- 

 guishes the third from the fourth. 



In respect to the first difference, the explanation is afforded 

 by the fact, made known by Delesse, that in chrysotile occurring 

 in the Vosges the fibres are swollen and changed to a white 

 colour when exposed to the atmosphere* (thus made acicular) 

 also by what has already been stated (and to be more fully 

 noticed presently) of the fibres in a specimen of chrysotile 

 from Reich enstein, which are occasionally fused together into 

 solid pillars : in certain cases the original fibrous structure has 

 disappeared. 



As regards the second, we hold that it, too, is demonstratively 

 explained by the specimen just referred to. Fig. 1, Plate II., 

 represents a layer of chrysotile between two of serpentine. The 

 specimen, for the purpose under consideration, was placed in a 

 weak solution of hydrochloric acid : a represents chrysotile in 

 its typical state ; b, the same passing into the state of closely- 

 * Ann. des Mines, ser. 4, t. xviii. p. 328. 



