Qwvt2 in Basalt. 127 



The large amount of quartz that must be present in the whole 

 flow, and its distribution through tin' same, although not uniform, 

 seems to debar the possibility of its having been picked up at the 

 crater as the lava came through originally; further, from the mode 

 of flow of a lava stream it is just as difficult to imagine how the 

 quartz could be picked up from the Moor of the valley, and distribute! 

 through the flow. The lack of any " pebble" form, and the extent 

 of chemical interaction with the magma also seem to militate against 

 this supposition. 



Some of the instances from England, South Africa, etc., which 

 have been investigated, and recorded, are apparently very similar 

 to this case, and for none of these was such an explanation advanced. 

 J. Cosmo Newbery, in a catalogue of Victorian rocks, published in 

 1894, says: "Quartz occurs in the newer basalt of Baringhup, 

 Maldon, frequently in grains and irregular patches of bluish-white 

 colour, and in such association with the rock as to leave no doubt of 

 its original formation in it." 



V.— General description of the Lava. 



The volcanic products of Mount Greenock may be roughly 

 described under three heads : — 



(a) Scoriaceous material; the mount is almost wholly composed 

 of this fragmentary rock, bombs are common, while ropy structure 

 and surfaces showing "flow" lines are of striking freshness. 



(b) The lower ledges of the mount show outcrops of extremely 

 dense compact basalt, very fine grained. 



(c ,N > The remainder of the flow, extending as a sheet southward, 

 and locally known as part of Nicholl's plains, is of a less fine- 

 grained type, often with a coarse doleritic texture, occasionally vesi- 

 cular, and generally resembling the material so common in the road 

 metal quarries of Ballarat or Melbourne. 



The general characters of these three types are set out below, 

 especially with reference to the quartz content as seen in the hand 

 specimen, and under the microscope. 



(a) The quartz in the scoria is generally very small in size; the 

 largest seen formed the centre of a small bomb, and was about j> in. 

 in greatest length. Crystals of 1 in. diameter are common, and 

 in a section cut where only one small piece of quartz was visible to 

 the eye, a dozen were revealed by the microscope. The scoria con- 

 tains abundant tiny idiomorphic felspars, a good deal of irivgular- 

 shaped augite, and son livine, with abundant glass. No sign of 



