744 THE TIN-DEPOSITS OF NEW ENGLAND, N.S.W., I., 



been recovered chiefly from the diamond-bearing gravels of 

 Tertiary age, which have been preserved by cappings of basalt. 



A further modification of the Tingha Granite occurs a few 

 miles to the south of Tingha. The difference is, however, mainly 

 one of texture. No phenocysts are present, and the granite is 

 rather fine-grained. 



The '^Acid Granite.'" — This granite varies considerably in tex- 

 ture, but very little in structure and composition. At Elsmore the 

 granite is rather coarsely crystalline, the crystals being about the 

 size of a pea. The rock is here composed almost entirelj' of quartz 

 and felspar. The felspar is predominantly orthoclase,while albite 

 is present in small quantity. The quartz-crystals are frequently 

 more or less idiomorphic, and micrographic intergrowth of quartz 

 and felspar is common Occasionall}' the granite takes on a 

 porphyritic habit, the felspars attaining a length of about an 

 inch. A very small amount of biotite and magnetite are usually 

 present, but in places even this is wanting. The granite has a 

 reddish colour, It is worthy of note, in this connection, that the 

 tin-bearing granite of the Waterberg District in the Transvaal 

 has been named the " Red Granite." (See Plate Ix., tig. 2.) 



The granite near Auburn Vale is similar to that at Elsmore; 

 rather more biotite is present; and a fine-grained modification of 

 it occurs. Micrographic intergrowth of quartz and felspar are 

 also very common. 



The granite at Howell is similar to the coarse type at Auburn 

 Vale; and the same tj^pe of rock occurs again intruding the 

 Tingha Granite at King's Gap. (See Plate Ix., fig. 3.) 



A modification of the " Acid Granite " occurs as an intrusion 

 into the Tingha Granite, about four miles south ol Tingha. Here 

 the granite, while possessing the usual characteristics of the 

 " Acid Granite," contains a good deal of microcline. It is in this 

 belt that Hong Hay's Pipe occurs. 



Another modification of the " Acid Granite " occurs at, and 

 near Tingha. This type occurs in small patches onl}', and is 

 notably tourmaline-bearing. It is miarolitic, the drusy cavities 

 being lined with quartz and tourmaline crystals. A fine exposure 



