22 Prof. W. King — On the Structure of a Rock from Ceylon. 



of analyzing the mineral ; but, considering it is slightly soluble in 

 dilute hydrochloric acid, the solution gelatinizing when concreted, — 

 that it has a somewhat pearly lustre, and is rather easily cut with 

 the point of a knife, we are led to refer it to wollastonite rather 

 than to any of the amphiboles : it moreover appears to agree with 

 the former mineral in its cleavage. 



The aggregations are generally in contact; but there are often 

 separations between them varying much in width, and filled with 

 calcite. The wide separations contain isolated aggregations, as well 

 as single grains, of various sizes : those that have not dropped out 

 or been detached consequent on decalcification remain partially 

 imbedded in the undissolved calcite. Interspersed amongst both 

 the wollastonite and calcite occur here and there microscopic gems 

 of different kinds ; while the common mineral silicates — ser- 

 pentine, (?) chondrodite, and others — are occasionally present. 



The precious stones, which appear to be variously-coloured spinels 

 — purple principally, opalescent moon-stone, and green chrysolite, 

 have no definite form ; being spheroidal, egg-shaped, more or less 

 cylindrical, or lobulated. They have polished surfaces, and seldom 

 display cleavage. A few present traces of angles, edges, and planes, 

 rendering it impossible to resist the conclusion that they are all 

 defacetted crystals which have been acted on by solvents that pene- 

 trated their imbedding rock. 



The same conclusion attaches to the wollastonite, as its various 

 aggregations and single grains display the plainest evidences of 

 waste, both internally and externally. Their cleavage divisions 

 (each formed by two juxtaposed planes in immediate contact in 

 minerals unaffected by disintegration) are of considerable width, 

 and filled with calcite. The single grains, also, are without any 

 definite form ; and, although their cleavage is well suited for pro- 

 ducing the bounding planes of a rhombic prism, their exterior is 

 rarely otherwise than jagged, variously excavated, or irregularly 

 rounded. Isolated fragments, reduced to mere skeletons, occur as 

 plates, rods, films, and shreds ; or under a variety of forms — 

 arborescent, curving, and infundibular. When the latter are in 

 clusters — with, as is often the case, a radiating, diverging, or brush- 

 like arrangement in each cluster — their beauty, increased by their 

 translucency and pearly lustre, altogether surpasses description. 

 And the sight is still more striking where the field of view is 

 additionally bedecked with different coloured gems. 



The configurations of wollastonite vividly recall to my mind the 

 typical examples of what have been erroneously considered as " casts 

 of tubuli of the canal system of Eozoon." Finer examples are not 

 to be seen in the Canadian ophites. In these rocks they invariably 

 consist of silicates, — generally serpentine, and occasionally a variety 

 of amphibole, or of pyroxene. 



It remains to be mentioned that the Ceylon rock has precisely 

 the same characters as a spineliferous urkalk (akerlyte) occurring at 

 Aker in Sweden. The principal mineral silicate of the latter was for- 

 merly considered by Dr. Eowney and myself to be malacolite ; but we 



