from Ceylon and the Coast of Coromandel. 33 



generally of a rounded and indeterminate form ; nevertheless, 

 on one of the specimens in the King's collection 1 observed 

 among them a complete hexahedral prism, and another with 

 many small facets on the edges of its terminal planes. These 

 crystals are but few in this gangue, which likewise contains, 

 in still smaller quantity, some small crystals of spinelle of a 

 pale-red or flesh-colour. They are even contained in the 

 substance of the dolomite; their form is either a regular octa- 

 hedron, a cuneiform octahedron, or an octahedron the edges 

 of which are replaced by a plane. The dolomite of this gangue 

 dissolves in nitric acid, without any sensible effervescence, 

 and with extreme slowness : a small fragment requires forty- 

 eight hours for its complete solution. It was found by 

 M. Leschenault very near Candy. It is likewise found, as 

 well as the two following gangues, in the isolated rocks at the 

 feet of the elevated mountains which separate Candy from Co- 

 lumbo, and upon the road which joins those two towns. 



The second gangue is likewise dolomite, in a lamellary 

 state, and formed, in the same maimer as the preceding, of 

 particular masses, but smaller and crossing each other in dif- 

 ferent directions. When first placed in nitric acid, it pro- 

 duces a very lively effervescence, which becomes weaker by 

 degrees, and at last very feeble. In a short time after it has 

 been placed in the acid, it becomes disintegrated into an 

 infinity of small particles, the greater number of which con- 

 tinue to dissolve very quickly. The analysis which has 

 been made of it gives more carbonate of lime than is neces- 

 sary to the composition of dolomite. I strongly suspect this 

 rock to contain some particles of carbonate of lime interposed 

 in its substance ; from which would arise the lively effect 

 of the acid upon coming into contact with it, its quick solu- 

 tion, as well as the disintegration which it undergoes. This 

 second gangue contains, in rather greater proportion than 

 the preceding, some flesh-coloured crystals of spinelle. It 

 also contains some very small crystals of mica of a very deep 

 yellow colour. Here and there likewise may be observed 

 some small crystals of pyrites, of the icosahedral variety; but 

 I have not observed any trace of phosphate of lime. This 

 gangue was found by M. Leschenault seven leagues east from 

 Candy. 



Although the third gangue of spinelle is from the same 

 district as the former, it is essentially different, and of a very 

 particular nature. It consists of very coarse grains, the tex- 

 ture of each of which is lamellated. Of these grains a very 

 great number are white, and their fracture has a very brilliant 



Vol. 63. No. 309. Jan. 1824. E lustre: 



