262 ROYAL SOCIETY OF CANADA 



hedral sections. The olivine and pyroxene have almost entirely excluded 

 these two and the melilite has also been well advanced before they began 

 to crystallise out. Apatite is present in very numerous needles. The 

 younger generation of biotite is generally small in amount, although 

 some slides show a considerable number of small flakes. Biotite is found 

 in the residues of former phenocrysts, where it is associated with calcite 

 and magnetite, melilite being frequently draped around the outside of 

 these cores. The garnet, apparently melanite, as has been already noted, 

 seems- to bear a direct relation to the amount of melilite present. Where 

 only in small amount, it shows partly developed crystal outlines with 

 strong zonary banding, — inside deep brown, middle golden-yellow, out- 

 side pale yellow. A few grains are altogether deep brown. The strong 

 optical anomaly displayed, is also in zones corresponding to those just 

 mentioned. The garnet seems to favour association with nepheline, this 

 relation holding not only when the garnet is small in amount, but also 

 when as in one case, it forms one-third of the slide. In this latter in- 

 stance the garnet is in granular aggregates in a groundmass chiefly com- 

 posed of nepheline. Nepheline forms the base of this rock although little 

 of it now remains, commonly having been changed over to cancrinite, 

 which is very plentiful in the positions usually occupied by the nepheline. 

 Tn one slide, nepheline is abundant in large individuals, showing a 

 poikilitic structure' enclosing the previously formed minerals. Calcite. 

 serpentine and chlorite are also present as secondary minerals. 



Several fine-grained, dark coloured spots were observed in the dyke, 

 and one of these was examined in thin section. It is composed of biotite, 

 olivine, garnet, apatite, perovskite, iron ore and doubtful nepheline. The 

 biotite is much the commonest constituent, in well preserved though 

 rather shreddy flakes giving a brilliant polarisation. Olivine is plentiful 

 in large well-formed phenociysts. Garnet is very abundant as small 

 crystals forming colourless to pale yellow masses. Apatite shows very 

 large phenocrysts, and numerous needles. Perovskite and iron ore are 

 very abundant, the former being rather ragged. Doubtful nepheline 

 forms what little base there is left. 



It will be at once observed that this description is similar to that of 

 the paste of the breccia and it seems reasonable to say that these dark 

 spots are fragments of the paste which have fallen into the dyke material. 

 The fact that the breccia is cut by a dyke of the same material as the 

 paste of the breccia, is readily explained as being due to surgings or 

 periods of advance and retreat of the magma. The first rise cemented 

 the fragments together and this mixture had at least nearly cooled when 

 a crack was developed and a further supply of molten material poured 

 forth, forming the dyke from the same material as composes the matrix 

 of the walls. 



