MICROSCOPIC STRUCTURE OF SOME AUSTRALIAN ROCKS. 229 



In the collection of slides presented with this paper there are 

 slices of many sedimentary rocks, claystones, sandstones, as well 

 as limestones. The sections of the limestones reveal nothing new 

 or noteworthy by a microscopic examination. Most of them are 

 of Silurian age, and from localities not yet recorded on our geo- 

 logical maps. They were collected at Mount Hope ; Rookery 

 Station, near Cobar; Twenty miles east of Rookery Station; 

 Baloura sixteen miles from Nymagee ; Mount Dijou, Curraweena 

 Station, south of Bourke. In the purely sedimentary rocks an 

 instance has been already noted of "strain structure" developed in 

 quartz grains, by metamorphism or pressure due to neighbouring 

 intrusive rocks and the slices of clay-slate rocks from Bathurst 

 are of considerable interest, as showing the change from a pure 

 claystone to a compact hornfels. 



Amongst the slices prepared, will be found also, some examples 

 of very fine serpentines from Mount Hope, Lucknow, Nyngan 

 and Gundagai, but their microscopic structure is almost identical 

 with typical serpentines so often described. 



Conclusion. 

 A microscopic examination of our rocks points to the existence 

 in Eastern Australia of every leading type from the vitreous to 

 the holo-crystalline condition, both acidic and basic, and their 

 general microscopic structure conforms to well known types of 

 described American and European rocks. 



In writing of American Basalts, Zirkel says,* "It is worth 

 while to pause, and remark that in these widely remote quarters 

 of the globe, the product of the solidification of a molten mass, 

 although exposed to many casualties has, nevertheless, maintained 

 a surprisingly close identity of microscopical composition." The 

 remark applies in every particular to the Australian basalts 

 described in this paper. 



Within well defined limits, the structure of our basalts shows 

 microscopical peculiarities that enable us to recognize certain 



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

 graphy, p. 253. 



