1866.] MACFARLANE — ON CUPRIFEROUS BEDS. 



Silica 14.73 



Alumina 7.17 



Peroxide of iron 14 . 87 



Lime 4.47 



Magnesia 2.03 



Water 3.09 



46.36 

 In the undeeomposed residue light red and dark coloured par- 

 ticles are discernible. On digesting it with hydrochloric acid 

 and subsequently with a weak solution of potash, it sustains a 

 further loss of 10.6 per cent., which consists of 



Silica 3.48 



Alumina 3.03 



Peroxide of iron 1 . 98 



Lime 1.76 



Magnesia 35 



The undecomposed residue was still found to consist of a light 

 red and a dark coloured constituent. The latter was the heavier, 

 and an approximate separation was accomplished by washing. The 

 dark coloured particles, which could not however be freed wholly 

 from the light coloured felspathic constituent, fused readily to a 

 dark brown glass. To judge from its gravity and fusibility 

 it would not appear unreasonable to regard it as either pyrox- 

 ene or hornblende. In quantity, however, it did not exceed one- 

 eighth of the felspar. The latter fused easily before the blow-pipe 

 to a colourless glass, tinging the flame strongly yellow. It would 

 therefore seem to be of the nature of labradorite, although it is 

 only slightly decomposed by hydrochloric acid. Since, according 

 to Girard, neither labradorite, nto pyroxene nor magnetite are 

 decomposable by nitric acid, it may reasonably be concluded that 

 the constituents removed by the nitric acid are those of the chlori- 

 tic mineral. On treating the rock, previous to ignition, with 

 hydrochloric acid, much of the iron is removed as protoxide. 

 Although some peroxide is also possibly present, I have calculated 

 the whole of the iron as protoxide, and have moreover added the 

 difference of weight between it and the iron as peroxide, to the 

 loss sustained by ignition, and put it down as water. In this way 

 the composition of the chloritic mineral calculated to 100 parts, 

 would be 



