358 



EEV. A. W. E0WE OX THE 



at all weathered ; the section shows it to be an ophitic hypersthene- 

 bearing dolerite, this being the only really ophitic dolerite that I 

 have found in the drift : the plagioclase is abundant, but much of 

 it is very cloudy : the augite fairly abundant, much cracked and 

 broken : there are several very good examples of hypersthene both 

 in grains and in distinct crystals, with the pleochroism from pale 

 watery green to orange or brownish red fairly strong ; some of the 

 crystals are much cracked and some almost filled up with dark 

 yellowish-brown alteration-matter ; in one or two cases a fibrous 

 structure has been developed. Xo. 93 is a remarkable rock, if it be 

 a genuine rock specimen and not a slag; it has all the appearance 

 of a slag, being very black and vesicular, and the magnetite is the 

 great feature of the rock ; but it is also composed of crystals which 

 polarize in bright colours, have some distinct outline, extinguish 

 on rotation, though not simultaneously, and have some appearance 

 of cleavage; its specific gravity is 4*51. The remaining specimen, 

 no. 94, is a plagioclase-augite rock of trachytic texture, of which the 

 plagioclase is the great feature ; for not only is it in abundant 

 microliths with remarkably di>.tinct fluxional arrangement, but some 

 la;ger crystals are enclosed, which are of anterior consolidation to 

 the ground-mass ; the section reveals a structure evidently very 

 similar to that of which Professor Judd speaks in his article on the 

 volcanic rocks of the north-east of Pife (Quart. Journ. Geol. Soc. 

 vol. xL p. 428), where he says, " the minerals of the second 

 consolidation consist of imperfectly developed microlites of felspar 

 .... the glassy base contains numerous trichites .... the dis- 

 position of these and the felspar microlites of the second consoli- 

 dation with respect to the larger porphyritic crystals reveals a most 

 striking flow-structure : not only are these minuter elements of the 

 rock arranged in irregular parallel bands, but they are crowded in 

 front and along the sides of the porphyritic crystals, trailing off 

 behind them." 



Granulites. — As these rocks are classed by some authors with the 

 eruptive rocks, and by others with the metamorphic rocks, I have 

 placed them here between the dolerites and the crystalline schists. 

 The only two examples which I have, nos. 95, 96, appear to 

 be specimens of the same rock, although found at different times 

 and in different localities. The rock is of a dark grey colour, of 

 a holocrystalline granular texture, and of a slightly schistose 

 structure ; the sections show that the rock contains plagioclase 

 and orthoclase in abundance, but chiefly the former, the crystals 

 showing signs of considerable strain, for they are much broken 

 and bent, and other crystals appear to have been forced between 

 the broken parts ; the hornblende is in granules, and there is much 

 secondary hornblende in cracks passing through the sections, and 

 in some cases through separate crystals, dividing them but not 

 apparently displacing the parts ; the rock also contains hypersthene 

 in abundance, in grains and crystals, and some biotite. Mr. Teall 

 kindly examined the sections for me, and he writes me that they 

 are very interesting rocks belonging to a well -characterized type. 



