80 THE ROYAL SOCIETY OF CANADA 



It is largely of secondary origin. A few laths and hexagonal prisms 

 of apatite are found sparsely scattered through the rock. 



Cavities up to 1.5 mm. in length, filled with calcite, are common, 

 and as the occurrence is apparently not closely connected with the 

 breccias, there is a possibility that the carbonate may be to some 

 extent of primary origin. 



The rock is, therefore, essentially composed of augite, with 

 subordinate biotite and diopside and very little olivine, in a 

 groundmass of sodi-calcic feldspar, nepheline, and glass, and may be 

 termed a camptonite with subordinate olivine, as nepheline-bearing 

 camptonites have been described from different localities in Eastern 

 America, associated with essexites and nepheline syenites. 



Nepheline Aplite. — Besides the camptonite described above, there 

 are also outcrops of a light grey coarsely crystalline rock which can 

 best be described as a nepheline aplite, although orthoclase is absent. 



In this section, the rock is found to be composed very largely 

 of nepheline, which has partially altered to thomsonite, with sub- 

 sidiary amounts of biotite and sodalite. A considerable amount of 

 black iron ore is present as well as some apatite and melanite. 



Nepheline with its alteration products make up fully 75 per cent 

 of the rock. This mineral occurs in irregular grains up to a centimetre 

 in length. Apatite and black iron ore are present as inclusions, the 

 former in regular crystal forms up to 0.5 mm. in length, and the latter 

 as minute grains scattered through the nepheline, and occasionally 

 as lines of minute specks. In some individuals these lines are sym- 

 metrically arranged, and intersect one another at an angle of about 

 60°. In the majority of cases, however, these inclusions are arranged 

 along the cleavage. The nepheline is also fractured, and alteration 

 has taken place along these fractures and around the border, resulting 

 in the highly biréfringent zeolite, thomsonite. 



Sodalite is present in rounded grains and is also partly altered to 

 thomsonite. The alteration product is present in far greater quantity 

 when associated with both nepheline and sodalite than with either of 

 these two minerals alone. 



Biotite occurs in very irregular flakes up to 0.5 mm. in length. 

 It is light grey-brown to dark greenish-brown in colour and contains 

 irregular flakes of black iron ore. This iron ore is usually associated 

 with the nepheline and biotite, and always occurs in irregular grains. 



Irregular and rounded grains of deep brown melanite are present. 

 This mineral displays the zonal structure typical of garnets, and in 

 places some of these zones are anomalously biaxial and negative. 



Transition Phase. — -The rock marking the transitional phase 

 between the camptonite and the nepheline aplite is largely composed 



