194 TERTIARY ROCKS OF AUSTRALASIA, 



ture is flat-conclioidal, with a glittering surface, 

 and it is sometimes rendered porphyritic by 

 crystals of hornblende and oligoclase, and grains 

 of olivine" (one of the varieties placed under 

 this group is described by Professor Ulrich as 

 nephe Unite), "having numerous crystals (hexa- 

 gonal prisms) of nepheline, some more or less 

 decomposed, besides large plates of black or 

 brown mica, patches of triclinic feldspar, appa- 

 rently oligoclase, crystals of black hornhleiide, 

 and large grains of titaniferous iron." This 

 variety is also in places characterised " by the 

 great abundance of zeolites, especially analcime 

 and natrolite." 

 (3) " Basalt, Basalt Lava. — Dark grey to mostly black, 

 quite homogeneous-looking ; in fracture gene- 

 rally somewhat dull, though in some places 

 . . . quite of the aspect of Lydian stone. 

 (a) " Earthy Basalt. — A bluish, greyish, or 

 brownish black, mottled, earthy-looking, 

 and more or less vesicular mass, with fre- 

 quently embedded nodules of a denser 

 texture, found in some places on top of 

 the plains, and also beneath sheets of hard 

 basalt. 

 (h) " Basalt Scoria. — Of dark brown or black 

 colour, highly vesicular or cellular ; the 

 vesicles or cells irregular in size and shape, 

 and showing glazed walls very similar to 

 some of the slags of iron furnaces. It 

 occurs in masses of irregular shape and 

 of all sizes, principally on the tops and 

 slopes of the craters and points of erup- 

 tion. The same is the case with — 

 (c) " Basaltic Pumice. — A scoria, so spongy 

 and light that it floats in water, and 

 might, except for its black or brownish- 

 black colour and absence of fibrous 

 texture, be mistaken for true trachyte- 

 pumice." (Occurs at One-Tree Point, 

 Hobart). 

 {d) " Basaltic Ash (Tuff). — Earthy and com- 

 pacted, ashy-grey or brown, sometimes 



