538 THE GEOLOGV OF NEWBRIDGE, NEAR BATHURST, N.S.W., 



first great bend in the railway line, where it passes into Augen 

 and Knotted Slates. It also occurs between the slate quarry and 

 the andesites. 



Macroscopically, very fine-grained, soft, light grey-green, with 

 good slaty cleavage and lustre. A little limonite is frequently 

 present in the cracks. 



Microscopically, almost identical with the Blue Slates; the 

 disposition and size of the quartzes is the same, and also of the 

 biotite crystals. The chemical change is chiefly in the biotite, 

 which has been largely altered to sericite, with the formation of 

 haematite and some chlorite. The accessories, tourmaline, anda- 

 lusite, rutile, zircon, and carbonaceous matter, are present, the 

 last being a widely varying quantity even in slates of the same 

 variety, since probably it was a varying quantity in the original 

 silt from which the slates were formed. Certain members of this 

 variety have special characteristics; one specimen contains a few 

 grains of oligoclase, another a great quantity of finely divided 

 andalusite. 



In this subgroup is classed the slate from the Caloola lime- 

 stones, though it differs from the type in several particulars. It 

 is to be regretted that the specimen was not obtained in situ^ 

 but only from the quarry debris. In hand-specimen it is of a 

 bright apple-green, rather coarser in grain than most members of 

 this group, slightly lustrous, and with a rather poor cleavage. 

 Microscopically it is chiefly quartz, showing the effects of rock- 

 flowage. Coloured minerals are less common than usual; the 

 biotite has been almost completel}' chloritised, forming feebly 

 pleochroic flakes of low double refraction. A little actinolite 

 occurs, and some muscovite; but there is little or no hsematite. 

 Tourmalines are frequent in grey-blue, pleochroic prisms; rutile 

 abundant in comparatively large yellow or brown needles, and 

 andalusite common in well developed, colourless, highly refracting 

 prisms with pyramidal, terminal faces. Zircons occur in the 

 quartz grains. 



The second variety of this group, Oxidised Slate, is very 

 abundant. It forms a band running down the eastern boundary 



