BY LEO A. COTTON. 743 



being usually present. In some instances, as at King's Gap, for 

 example, fragments of the Tingha Granite may be seen included 

 in the "Acid Granite." 



The Tingha Granite is typically developed around Tingha, 

 chiefly to the south of Cope's Creek. A glance at the accom- 

 panying map shows its extent. It is characteristically a 

 porphyritic granite, the phenocrysts being felspars and quartz. 

 The felspars are chiefly plagioclases, and may be seen rather 

 more than an inch in length, though typically they form almost 

 square crystals, about half an inch in length. A considerable 

 amount of biotite, and an almost equal quantity of hornblende 

 are present. Apatite is an accessory mineral. The quartz 

 grains are seldom larger than a pea, and are less numerous than 

 the felspar phenocrysts. The ground-mass consists of a second 

 generation of felspar and quartz. The felspar phenocrysts cause 

 the rock to present a striking appearance on weathering. It is^ 

 remarkable that the felspars, usually so prone to decomposition, 

 stand out in bold relief, often projecting a quarter of an inch or 

 more above the surface of the rock. This is due, no doubt, to the 

 more rapid weathering of the second generation of felspars, 

 causing the rock to disintegrate round the phenocrysts. 



This granite occupies a considerable area, and was the first ta 

 intrude the sedimentary rocks. An isolated area of it occurs in the 

 neighbourhood of Copeton, and extends a few miles to the north 

 of that town. This granite is represented by Plate lix., fig. 2. A 

 somewhat similar granite, which may be regarded as an allied 

 type, is the Oakey Creek Granite. This rock extends from near 

 the Inverell to Copeton Road, for a considerable distance to tlie 

 west. It is extremely porphyritic, the felspars attaining a 

 length of nearly three inches in rare cases. The average size is 

 considerably more than an inch in length. Pegmatite veins are 

 common, and dykes of a fine-grained felspathic nature containing 

 a good deal of tourmaline are also abundant. Quartz veins con- 

 taining large prismatic crystals of tourmaline are also to be 

 found. 



Stream-tin has been discovered in small quantities throughout 

 the area, but no lodes have been worked. The cassiterite has 



