224 REV. J. MILNE CURE AN. 



it probably represents extreme alteration of a sedimentary rock. 

 The quartzes in the slice exhibit " strain figures " much more 

 perfectly than I have noticed in any other Australian rock. 

 These strange shadows can be seen both in ordinary and polarized 

 light. 



Slice 145. — Hyalite from Springsure, Queensland. I have 

 noticed splendid examples of hyalite in the basalts of Springsure, 

 Queensland. Under the microscope they are quite clear and glassy. 

 Between crossed nicols these hyalites show a certain amount of 

 colour. From their constitution as amorphous silica they should 

 remain dark. This colour I should attribute to internal strain 

 rather than to any admixture of amorphous and crystalline silica. 



Slice 151. — Quartz-felsite from twelve miles south of Dubbo, 

 New South Wales. This rock might be called an altered rhyolite. 

 In hand specimens wavy lines, caused by a flow structure, are 

 readily recognised. Under the microscope, instead of sphserulites 

 a radial arrangement of microlites is seen set around a linear axis. 

 Zirkel describes similar but more pronounced structures in some 

 American rhyolites.* 



Slice 104. — Intrusive rocks are so rare between Cobar and the 

 Darling, that there is a special interest in recording an altered 

 diabase from the Black Hills. The rock is vesicular, but all the 

 cavities are filled with well crystallized calcite. The crystallized 

 amygdules show the peculiar crossed striae of calcite remarkably 

 well. (Plate xxn., Fig. 1.) There is no recognizable pyroxene 

 in this rock, but the large amount of chlorite which is present is 

 most probably a secondary mineral derived from the alteration of 

 the augites. The chlorite, moulded around and along the plagio- 

 clase laths, is certainly of secondary origin. I have cut about 

 twenty slices of these rocks and they all present the character of 

 this slide and Plate xxn., fig. 4. 



Slice 134. — It has been stated more than once that the immense 

 metalliferous deposits of Cobar are intimately connected with 



* U.S. Geol. Explor. Fortieth Parallel, Vol. vi., Microscopical Petro- 

 graphy, p. 167. 



