MICROSCOPIC STRUCTURE OF SOME AUSTRALIAN ROCKS. 231 



new one, namely mica. This corresponds with observations made 

 on similar rocks in other parts of the world. 



The wide distribution of Tertiary leucite rocks in New South 

 Wales is a matter of considerable interest. 



The specimens with which this paper deals have been collected 

 over widely separated localities. There is material enough in any 

 one district, for considerable petrological research, but it has 

 been my purpose rather to indicate the wealth and variety of our 

 material for work, than to give exhaustive details of any one field. 

 Much of the matter furnished will I trust, prove new, and of 

 some interest to Australian Geologists. 



EXPLANATION OF THE PLATES. 



Plate xx. 



Figs. 1 and 2. — Tachylyte from near Pratt's, Carcoar, as seen magnified 

 50 diameters, by ordinary light. Globospherites resembling sphaerulites of 

 devitrified matter, are surrounded by halos free from globulites, or other pro- 

 ducts of incipient crystallisation. 



Plate xxi. 

 Fig. 1. — Basalt, from Orange, New South Wales, as seen magnified 50' 

 diameters, in ordinary light, illustrating a type of structure common in 

 Australian Basalts. The slice shows a "felted " mass of lath-shaped felspars; 

 in the spaces between these felspars, olivine, augite, magnetite, and some 

 glassy matter are developed. 



Fig. 2. — Basalt, from Perth, near Bathurst, New South Wales, as seen 

 magnified 50 diameters by ordinary light. Illustrating the microscopic 

 structure of a micro-porphyritic Basalt. Porphyritic crystals of olivine, 

 augite, and felspar, are set in a ground mass composed of granules of augite,. 

 olivine, and magnetite. 



Plate xxn. 



Fig. 1. — Altered diabase, Black Hills, Oobar, New South Wales, as seen 

 with inclined nicols, and magnified 30 diameters. The cavity in the centre 

 of the figure has been filled by secondary calcite, which is seen transversed 

 by characteristic fine cleavage lines, intersecting at an acute angle. 



Fig. 2. — Triclinic felspar in Granite, Moruya, New South Wales, as seen 

 with crossed nicols, under a magnifying power of 20 diameters. 



Fig. 3. — Micro-porphyritic Basalt, German's Hill, Canoblas, New South 

 Wales, as seen in ordinary light, with a magnifying power of 25 diameters. 

 A large augite is set in a very fine grained basalt. 



