Smyth — On a Variety of Finite occurring at Bally corns ^ Co. Dublin. 493 



instance, there were four convenient angles. Three of these scratched Iceland 

 spar ; the fourth would not. The latter corner scratched selenite. 



Measurements of specific gravity were made by means of methylene 

 iodide, diluted with xylol, on very small particles obtained by crushing. 

 The specific gravity of the liquid was found with a Westphal balance. The 

 highest results are considered the most reliable, for(l) the microscope showed 

 that the chief impurity was quartz, and the specific gravity always came 

 out higher than that of quartz ; (2) dull specimens known to be impure gave 

 low results ; (3) the more finely divided material gave a higher proportion 

 of heavy grains. 



Chemical Analysis. 



The result of a chemical analysis of five or six gi-ams of the most carefully 

 picked material is shown in column I of the table. One chip of the same lot 

 was sliced for the microscope in order to gain an idea of its purity. It contains 

 a remnant of a disintegrating felspar crystal and some minute granules of 

 quartz, but the great bulk of it is of one kind of material of uniform texture. 



I. — Finite, Ballycorus, Co. Dublin. 

 IT. — Average of 19 analyses of muscovite quoted by Dana (Syst. Min., 

 6th ed., pp. 617-8, analyses 1 to 19, inclusive. 1911). 

 III. — -Average of 12 analyses of pinite (loc cit., p. 622). 



