1865.] MACFARLANE— GEOLOGICAL SKETCH OF ROSSIE. 275 



bed of the ore, and the underlying shale, deviates very much from 

 the horizontal. Two specimens of ore taken from this bed con- 

 tained, 



Best ore. Inferior ore. 



Silicious matter 4-80 2-18 



Peroxide of iron 93-15 = 65-22 iron 66*00 = 46-21 iron. 



Carbonate of lime 2-05 32-40 



100-00 100-55 



Since the ore together with silica often forms the cement of the 

 breccia above mentioned, it is highly probable that the sandstone 

 was deposited, and also disturbed prior to the formation of the 

 masses of ore. With regard to the origin of the latter, it is impos- 

 sible to regard them as igneous products, when we consider the 

 large amount of earthy matter which they contain. And, further, 

 the absence of specular iron ore would seem to indicate that they 

 could not have been the result of any process of sublimation. 

 There only remains, therefore, as adequate to explain their mode 

 of formation, the theory that the ore was introduced into its 

 present bed in the state of solution, and deposited there by means 

 of some precipitating agent. A slight degree of heat may sub- 

 sequently have been instrumental in converting the precipitate 

 into anhydrous peroxide of iron. 



There only remains to mention, in connection with the econoi, ic 

 minerals of Rossie, the vein of magnetic and iron pyrites occurring 

 in the diorite already described. A very considerable amount of 

 exploration has been done on this vein in search of copper, but 

 mere traces only of copper pyrites are sometimes observable close 

 to the quartz which forms part of the veinstone. The magnetic 

 pyrites contains no nickel, and the least trace of cobalt. The 

 iron pyrites, on the other hand, contains no nickel and 0-85 per 

 cent, of cobalt. 



I here conclude this geological sketch of Rossie. It is neces- 

 sarily very incomplete from the limited time at my disposal when 

 visiting that place. I trust, however, that it will be found to con- 

 tain a few facts of interest. 



Acton Vale, C. E., 29th May, 1865. 



