On the Norian or " Upper Laurentian " Formation. 195 



quantity of iron ore is considerable only in a few places, and 

 as in these cases the percentage of pyroxene increases in 

 the same proportion, the rock here assumes a very dark 

 colour so that it is often taken for an iron ore. These por- 

 tions of the anorthosite rich in iron ores are only few and 

 local, and they pass over into the normal gabbro of the area 

 which as above mentioned is very poor in iron ore. 



If these iron ore grains are examined by reflected light, 

 they are seen to be black and in a few cases they cau be 

 seen to be partly changed into a grey decomposition pro- 

 duct, evidently a variety of leucoxene. This circumstance 

 proves that the mineral contains titanic acid in consider- 

 able amount. 



In three hand-specimens from widely separated parts of 

 the area an intermingling of two iron ores was distinctly 

 seen. In one of the hand-specimens which comes from 

 Wexford, range I. lot 7, one of the above mentioned locali- 

 ties where the anorthosite is rich in iron ore, careful obser- 

 vation in reflected light showed the iron ore to occur partly 

 as a bluish black coarse grained variety, and partly as a 

 brownish black finely granular variety both being irregu- 

 larly intermingled and distinguishable only by reflected 

 light. 



When the section was treated for about half an hour on 

 a water-bath with warm concentrated hydrochloric acid, 

 the coarsely granular variety was entirely dissolved and 

 the acid became strongly coloured with iron, while the 

 finely granular variety was apparently not at all affected. We 

 have evidently here an intergrowth of magnetite with 

 ilmenite or at least with a titaniferous iron ore. 



In another hand-specimen (from the neighbourhood of 

 Lake Ouareau) a similar intergrowth was observed ; the 

 grains had a banded appearance in reflected light, one 

 variety crossing the other in a single or double set of inter- 

 rupted bands. When the section was treated with cold 

 concentrated hydrochloric acid for 48 hours, no effect was 

 produced ; but when treated with warm concentrated acid 

 in a water-bath, one variety of iron was dissolved as before 



