381 



throughout the rocks in small and inconspicuous particles, and talc is quite 

 abundant, often with numerous magnetite grains embedded in it. An original 

 fine-grained f erromagnesian mineral and what appears to have been a glassy base, 

 whose former presence is strongly suggested by the present textural features, 

 have been transformed into iron oxide, chlorite (pennine), and talc. 



The amygdular inclusions are constituted of faintly blue-green chlorite and 

 a fine scaly mineral corresponding to talc. To a minor extent microscopic 

 granules of quartz and calcite are present. 



The original rock was evidently an amygdaloidal basalt, but as a conse- 

 quence of great antiquity has suffered recrystallization. Except for the steam 

 holes and their fillings this rock closely resembles in microscopic features the 

 chloritised basalt described from the Blinman South Mine by W. N. Benson.*^') 



The other four specimens of similar type to that just described vary only 

 in minor details of structure and in quantities and modifications of the original 

 minerals. They range from a chocolate-brown to a warm-grey colour, as noted 

 in the hard specimen ; also there is a noticeable variation in the quantity and 

 character of the vesicles now filled by secondary minerals. 



Judging by the development and distribution of the plagioclase laths, as 

 seen in the microscope slide, the original structure probably ranged from true 

 doleritic forms to pilotaxitic and to almost hyalopilitic types. There is some 

 variation in the changes which afifect the plagioclases, but rarely in any relic 

 left of original twinning. The quantity and distribution of the iron ores is 

 variable. Magnetite is partly in tiny original idiomorphic crystals and as a 

 secondary dust. Plagioclase needles are noted to show flow structure around 

 certain of the large magnetites. Limonite and hematite are much more abundant 

 in some specimens than in others, and very much affect the prevailing colour 

 of the rock. In all cases original pyroxene and glassy base have changed to 

 chlorite, talc, and dusty iron ores. In one specimen occasional grains of yellow 

 epidote are to be seen. 



The vesicles are usually very irregular in form, and longish flattened ones 

 are present up to three-quarters of an inch in length. In one case a crack 

 extending over a considerable area in the specimen is also filled in the same 

 manner as the vesicles. The usual filling of these is a pinkish peripheral layer 

 of what is apparently quartz clouded with ferruginous dust. Within is a whiter 

 area in which are variable proportions of granules of clear quartz, talc, chlorite 

 (pennine), and much more abundant calcite, which usually occupies the central 

 zone. In one rock only, grains of yellow epidote also appeared in the vesicles, 

 and in another case chalcedony was noted. 



The other class of amygdular melaphyre collected by Mr. Greenwod is of a 

 striking appearance. It is an aphanitic grey rock packed with spherical white 

 amygdules. Thus in its general appearance it recalls some leucitophyres. 



In microscope section it is seen to be composed of recrystallized plagioclase 

 needles in a base dusty with fine magnetite and composed largely of chlorite 

 with low double refraction. There are also ramifying patches at intervals of a 

 fine scaley mineral of high double refraction either talc or white mica. The 

 original structure appears to have been hyalopilitic. 



The amygdules are mainly filled with quartz in the form of elongated 

 granules usually arranged in a rough sub-radial manner. The only other mineral 

 of the vesicles is what is apparently white mica in aggregates of the most minute 

 particles. This latter mineral is never present in quantity and is usually dis- 

 posed peripherally. 



f') Trans. Roy. Soc. S. Austr., xxxiii., 1909, p. 226. 



