On the Metamorphic Rochs of Counties Sligo and Leitrim, 365 



Analysis II. 

 Containing much Magnetite in Bands. 



99-65 

 Analysis III. 



Another portion of same Specimen. 

 This gave magnetite 1 4'35 per cent,, but does not materially 

 affect a prismatic compass. It, however, strongly affects a delicate 

 needle. 



The de-magnetised portion had the following composition : — 

 SiOo, . . . . 39-20 



MO, 

 Fe,03 

 FeO, 

 Mn 



NiO, . . . , 1-00 



Ca O, . , . . 1-00 



MgO,t . . . . 34-48 



"Water, .... 13*25 



O3, ( 



o, ) 



11-80 



100-73 



Note The general relation of the silica magnesia and water in this analysis closely 



resero-'jles that given by Dr. Haughton of the red serpentine of Cornwall. (Phil. Mag., 

 vol. 10, p. 253, and Jukes and Gerkin, p. l42. 



I have not estimated the proportion of peroxide of iron, or 

 protoxide of iron and manganese in this specimen. But I may 

 mention that the amount of peroxide is very small, and the greater 

 bulk of the united weight is due to the alumina. It contains 

 3"75 per cent, of protoxide of iron. 



Besides the above I have made several partial analysis of other 

 portions of the rock, but they possess no particular interest except 

 that they show the rock to be throughout of very similar com- 

 position, invariably containing alumina and magnetite, with nickel 

 sometimes reaching up to 2-5 per cent. 



* In this analysis there is some uncertainty as to the presence of Feg O3 . 



f Other specimens of the rock gave 35-00 and 36*45 per cent., magnesium oxide. 



SciEN. Bkoc, R.D.S., Vol, m., Ft. vi. 2 F 



