228 



not idiomorphic but partly ophitic. Chlorite occurs in irre- 

 gular patches. Ilmenite, partly changed to leucoxene, is 

 present in large amount, and rutile needles may be found. 

 The vesicles are lined with matter pennine ( ?), which is fol- 

 lowed by a layer of fibrous radiating clinochlore (or perhaps 

 delessite). The central portion is of epidote and quartz. 

 This rock also is an amygdaloidal melaphyre. 



From Mr. Slee, B.E., I received a specimen of a basalt 

 occurring near Broken Hill. It is much finer in grain than 

 the preceding rocks, is of a light-grey colour, and its few 

 vesicles are filled with calcite and epidote. Microscopicall}' 

 it is also microgranulitic. The felspar is of one generation 

 only, is fairly fresh, and is probably oligoclase. It includes 

 small needles of actinolite. The augite has become uralite, 

 and its fibres extend far beyond the original limits of the 

 grain. Magnetite is very abundant, though not so much so 

 as in the Blinman melaph3're. It occurs in small grains and 

 octahedra. Clear-green serpentine pseudomorphs after oli- 

 vine are present in some amount, crossed and bordered by 

 magnetite, and including small colourless epidote grains 

 (clinozoisite). Pale- or bright-yellow epidote (pistacite) is 

 common between the felspar laths or less regularly placed. 

 Chlorite also is present in matted-green areas of low aggre- 

 gate polarization. Calcite is present in large lenticular 

 patches in the rock, often with pistacite. Quartz occurs spor- 

 adically, and is probably secondary. The rock is a melaphyre 

 closely allied to the spilites. 



II. — The Diabases. 



The Blinman diabases can be subdivided for the purposes 

 of this paper, on mineralogical and textural criteria, into the 

 olivine-diabases, ophitic-diabases free from olivine, granu- 

 litic-diabases, and gabbro-diabases. Between the last three 

 the distinction is by no means a sharp one : the textures in 

 the freshest rock may pass gradually from one into the 

 other, and the extreme alteration of many of the rocks makes 

 distinction still more difficult. 



OLIVINE BI ABASES. 



The dyke or neck on the west side of Blinman Mine is 

 composed of a fine-grained compact rocl<^, containing small 

 crystals of felspar and a dark-green silicate. Microscopically 

 (see fig. 2, pi. xv.) it is ophitic in texture. The predomi- 

 nant mineral is a pale or colourless augite, comparatively 

 fresh, though in places it is altered in a peculiar fashion. 



