BY R, M. JOHNSTON, F.L.S. 195 



mottled in these colours ; found near 

 craters and points of eruption, frequently 

 in stratified layers. The compacted kinds 

 are in some localities (Warrnambool, 

 Terang, &c.) advantageously used as 

 building stone, being, when freshly broken, 

 soft enough to be sawn into blocks of all 

 sizes, but hardening considerably on ex- 

 posure to the atmosphere." 

 '' Both the older and newer basalt rocks are rich in 

 accessory minerals, partly original, partly of secondary 

 origin. As the most noteworthy original mineral may be 

 mentioned. Olivine — common in all our basalts, but more 

 especially characteristic of the newer ; in fact it is so 

 frequent in places (Deloraine, Table Cape) as quite to 

 assume the place of an essential constituent of the rock. 

 It is generally of an olive-green, sometimes emerald and 

 bottle-green colour, has a glassy lustre, and appears in 

 grains and larger and smaller nests or polygonal masses 

 of granular texture, up to several pounds in weight, irregu- 

 larly distributed through the rocks. ... It seems to 

 decomjoose more readily than the mass of the rock, leav- 

 ing behind it a reddish-brown substance, principally con- 

 sisting of hydrous ferric oxide." 



In their mode of occurrence, the three sub-species and 

 their varieties, so graphically described by Professor 

 Ulrich, differ in some respects from those described from 

 basalt districts in Europe, inasmuch as they do not always 

 occur in distinct masses with defined outlines, but rather, 

 as described by Professor Ulrich, whom the author has so 

 largely quoted, they " form here rather irregular portions 

 of undefinable size and shape, graduating one into the 

 other, laterally as well as vertically throughout the same 

 sheet or stream of lava. They present, in fact, only as it 

 were, differing forms and stages of mineral aggregation 

 during the cooling of the molten matter. The same quarry 

 yields thus frequently both anamesite and basalt, and at 

 Malmsbury a quarry produces, besides these, oho dolerite." 

 It is evident, from a study of these igneous rocks, that 

 the eruption from the same point took place again and 

 again after considerable intervals of repose, and this is 

 substantiated at One-Tree Point, at Hobart, and also at 

 Geilston, by the discovery of bone breccia lying under a 



