36 Transactions. 



be seen, but most of tlie crystals are rounded or irregular]jin shape, and are 

 interrupted in crystallization by inclusions, so that the form is like a sj)onge. 

 Spliene and quartz are found in the pores of the sponge, and also independ- 

 ently in the calcite. Finally there is a little pyrites. 



This collection of rocks, interesting as it is in itself, throws little light on 

 the question of assimilation. Certainly there are many points of resemblance 

 with the Pyrenean granite-contacts, but the endomorphic modifications of 

 the granite are too poorly represented to draw a parallel. A complete 

 investigation would involve the detailed mapping of these basic facies with 

 the rocks at their contact. Even then, the phenomena would admit of 

 either interpretation, unless a thorough chemical examination of both classes 

 of rocks conclusively proved the absorption of the earthy bases. Probably 

 the truth will be found to lie between the extreme positions, a partial assimi- 

 lation accompanying laccolitic differentiation. This paper will serve its 

 purpose if it draws attention to this interesting question. 



Part II.— Bluff Hill. 



The rocks here described are the result of a few hours' collection along 

 the shore south and west from Bluff Harbour. Immediately joining the 

 harbour is a series of apparently bedded rocks, which are in some cases so 

 dense as to resemble hornstones, but in other cases suggest sheared porphyritic 

 igneous rocks. A section of one of the denser varieties proves the rock to 

 be a fine-grained banded hornblende schist. Some of the bands are richer 

 in hornblende, others in epidote and iron-ores, while a mosaic of polygonal 

 quartz grains is common to both. Apatite is not rare, and rutile is very 

 abundant in minute prismatic crystals with pyramidal terminations pro- 

 jecting out of quadrate magnetite crystals. A similar mineral occurs in 

 more rounded crystals in the quartz, and is difficult to determine with cer- 

 tainty as rutile or sphene, but there are a few xmdoubted larger crystals of 

 the latter. The hornblende, a common green variety, occurs in prismatic 

 crystals mostly parallel to one another, more rarely oblique to the schistosity. 

 Sometimes the crystals are so slim and needle-like as to simulate sillimanite 

 needles. Cross-sections show that in addition to the prismatic faces the 

 B pinacoids (010) are present, a feature rarely observed in hornblende schists. 

 The epidote does not show clear crystalline form, but occurs in granular 

 aggregates elongated in the same direction as the hornblende. The crystal- 

 loblastic order appears to be apatite, magnetite, rutile, sphene, hornblende, 

 epidote, and finally quartz. 



A vein of coarser grain separates the hornblendic and epidotic bands, 

 and contains, besides hornblende, epidote, and quartz, a few large twinned 

 basic feldspars. The absence of albite in the rock is surprising if it is derived 

 from an igneous or pyroclastic rock. Untwinned feldspar is always difficult 

 to recognise in the presence of quartz, but an examination of as many of the 

 colourless grains as possible in convergent light gave only uniaxial figures. 

 From the absence or relative paucity of feldspar the rock has more affinities 

 with a para-hornblende-schist than with an ortho-hornblende-schist. It 

 presents many points of resemblance to the " green schists " among the 

 Old Lizard Head series of Cornwall. 



A dyke of a dark porphyritic rock crosses the schist formation at an angle 

 approaching 45°. In section this rock also proves to be quite schistose, 

 but, unfortunately, the directions of schistosity of the dyke and the intruded 

 schists were not compared in the field. The phenocrysts consist of large 



