128 Charles Fenver: 



reaction rims could be detected around the microscopic quartz; 

 grains, although the shapes suggested that corrosion had taken 

 place. Hyalite is common, lining cavities in the scoria. 



(b) The second type of basalt hardly appears to contain any 

 quartz, ruder the microscope the rock consists of a ground-mass 

 of glass and oxides of iron, packed with tiny acicular felspars, and 

 dotted with porphyritic olivine. There is very little augite present, 

 which is rather a contrast to the third type of rock, where augite is 

 common. The most definite augite present in this dense type con- 

 sists of the tiny green pyroxenic needles forming the reaction rim 

 around one of the rare pieces of contained quartz. 



(c) This third type is that of the main flow. As stated, the 

 appearance in hand specimen is quite similar to that of the great 

 majority of the Victorian newer basalts, except that in places 

 throughout the mass it is thickly mottled with corroded quartz. 

 In addition, quartz fragments occur sparsely right throughout the 

 flow. These are quite uncommon as microscopic pieces, but range 

 from | in. diameter up to f in., and even larger, one mass seen 

 being 14 inches in diameter. 



In the hand specimen the quartz shows a great amount of frac- 

 turing, and is sometimes surrounded by a minutely vesicular discon- 

 tinuous border. It very frequently has a peculiar chalcedonic lustre, 

 but is mostly dull-grey in colour. Where the quartz is most abun- 

 dant, hyalite occurs, and was always noted on the roofs of the 

 containing cavities (Fig. 2). 



Under the microscope the rock is of a coarse doleritic texture, 

 with large felspar laths, interspersed with granular augite, and 

 abundant porphyritic olivine. Apatite is present, in bunches of 

 needle-like crystals, and iron oxides occur throughout. " Con- 

 traction vesicles " are also common. 



Where the quartz comes into contact with the other minerals of 

 the rock, there is always a reaction rim of pyroxenic material, with 

 sometimes a thin band of glass separating it from the quartz. This 

 border is sometimes granular, darkened apparently by the presence 

 of iron oxides; at other times the pyroxene prisms are parallel, 

 roughly normal to the edge of the quartz, presenting under crossed 

 nicols a very pretty appearance. Fig. •'? shows these typical relations 

 diagrammatically. 



The quartz shows abundant inclusions, running in lines through 

 the mineral, and negative crystals were observed. The larger pieces 

 of quartz ar e not single crystals. Along many of the fractures. 



