ROGERS, GEOLOGY OF THE CORTLA^DT SERIES 39 



having been derived by paramorphism from augite. In the former area, 

 the coarse green hornblendes often contain patches of altered but still 

 recognizable augite, and these are undoubtedly secondary; but some of 

 the hornblende may well be original. If this be so, the primary rock 

 was a hornblende pyroxenite. Finally, hornblendite occurs in the net- 

 work on Montrose Point, apparently there also derived by paramorphism 

 from pre-existing pyroxenites. These two modes of origin thus appear 

 to have both been operative in the formation of the hornblendites. 



The rocks are easily recognizable in the hand specimen; they are 

 usually medium coarse in grain and glistening black in color, with prac- 

 tically no white minerals. In the rock of the first patch referred to (at 

 Lake Meahaeh), there is a little feldspar present, less than one-fifth of 

 the rock ; a small proportion of it is unstriated. The hornblende consti- 

 tutes the great bulk of the specimen ; it is pleochroic from yellow to dark 

 brownish green in some cases, while in others it is distinctly brown, 

 with a very small extinction angle. These two varieties may occur to- 

 gether in a single specimen. Sometimes the magnetite inclusions become 

 so abundant, especially in the green variety, that all light is shut off ex- 

 cept at the margin of the crystal. Hypersthene may be present in small 

 amount and biotite in larger quantity. The grain of the rock in this 

 area changes very suddenly from coarse to unusually fine. 



In the area south of Montrose, the rock is similar to the above. The 

 hornblende is always brownish green, with extinction averaging about 

 20°. Biotite is a trifle more abundant and occurs as aggregates of crys- 

 tals in the hornblende. Irregular masses of pyrite and pyrrhotite are 

 common. Calcite has developed to some extent. 



In the more westerly of the two other areas, the rock is much the 

 same, but the brown hornblende is apparently pseudomorphic after au- 

 gite, and traces of the latter may still be seen. There is a moderate 

 amount of biotite and several distinct alteration products, such as chlo- 

 rite, calcite and quartz. There is no feldspar. 



The structure in the easternmost area has been described; the horn- 

 blende is sometimes in large coarse t green crystals, and sometimes in a 

 confused lighter green mass, which is partly chlorite. The remnants of 

 the augite may still be seen. 



The process of paramorphism is thus clearly indicated, and there can be 

 no doubt that this is the common mode of origin of the hornblendites. 

 In the two areas in the diorite, this is by no means impossible, since 

 pyroxenite is apt to occur around inclusions in the main body of igneous 

 rocks, and these two patches are both near inclusions. There is shown, 

 however, in the writers suite of specimens from this district, a fairly 



