BY W. N. REXSON. 365 



roc-k with small phenocrysts of augite and albite. lii ; trueture, it 

 is closely comparable with the usual types of spilite in the Eastern 

 Series, but it ha.s been ratlier crushed. The highly altered pillowy 

 spilites and associated dolerites in Portion 56 remain to be men- 

 tioned. The dolerite (1377) was originally ophitic, and though the 

 rock has been completely decomposed, the structure has been 

 retained. The felspar has been replaced by strained (juartz and 

 chlorite, the latter when forming a large area being generally 

 spiiernlitic. Tiie silica is sometimes ehaleedonic, and may have 

 narrow margins of carbonate. A second form of alteration is to 

 calcite, with a small amount of I'esidual albite. The augite is 

 entirely changed to platey chlorite. A little magnetite remains. 

 The spilites forming the pillows are represented by Nos. 1112 and 

 1 1 24. In these, the original structure is more or less lost, owing to 

 the decomposition of the constituent minerals. Traces, however, 

 indicate that the felspar formed prisms, which are now replaced 

 eitlier by chlorite (1124) or a clear, colourless, intermediate 

 material (1112), which is perhaps a zeolite. The pyroxene w^as 

 idiomorphic (1112) or ophitic (1124), and is now^ changed to 

 chlorite in green plates with splierulites, or associated with dolerites 

 or calcite. The formation of chlorite is accompanied by the 

 sejiaration of magnetite. 



TliP Igncoiin Rochs in tlip Tmnwoiih Serifs. 

 The Dolerites. 



The Dfjleritrs icit]i hasic felspar occur in tlie nortliern of the tw^o 

 series of intrusions already described, those with albite are in the 

 southern intrusions. The freshest example of the first group is a 

 rock (1387) from the large intrusions in Portions 24, 35. It has 

 a structure intermediate between the granitoid and subophitic. 

 The felspar is strongly zoned, tlie main portion being labradorite. 

 the margins of the grains oligoclase. The ferromagnesian minerals 

 are abundant, augite in sub-idiomorphic grains being predominant. 

 Hypersthene, however, occurs in considerable amount in large, 

 roughly idiomor]ihic grains (upon which tlie augite is sometimes 

 moulded), occasionally containing idiomorphic plagioclase. Tlie 



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