1872.] DAINTREE GEOLOGY OF QUEENSLAND. 295 



examined in polarized light, are of course triclinic, whilst those of 

 one colour are probably orthoelase. There are some twins showing- 

 two colours sharply divided by the Hne of junction of the two 

 halves ; and these are certainly orthoelase. 



" The secondary products are a little chlorite, and two or three 

 blebs of quartz, filling spaces between the crystals. 



" The rock is not much altered." 



Of the f OSS iliferous tufa he says : — 



" It is a fragmentary rock, and has undergone so much alteration 

 that the constituents cannot be well identified. There are, however, 

 some grains of augite and magnetite. The fragments are imbedded 

 in a chloritic base, which is itself a product of alteration." 



Of another specimen of the same character from the West-coast 

 Reef, Gympie, he remarks : — 



" This is a characteristic trappean ash or breccia ; it consists of 

 numerous fragments of rather fine-grained trap-rocks, broken crystals 

 of felspar and augite, many black grains of magnetite, and fragments 

 of other rocks, the whole forming a compact mass in which there 

 is now much chlorite." 



The analysis of the crystalline rock indicates no very determinate 

 results,- but suggests the presence of two felspars and two varieties 

 of hornblende, with a little chlorite, carbonate of lime, and pyrites. 



The insoluble portion may be a mixture of perthite and an insoluble 

 aluminous hornblende, whilst the soluble portion indicates a mixture 

 of oligoclase, an iron and magnesian hornblende, like pargasite, and 

 a smaller proportion of a chloritic mineral, as indicated by the water 

 of constitution. 



The absence of augite in its composition would, notwithstanding 

 the presence of the products of decomposition, chlorite and carbonate 

 of lime, place it among the diorites. The so-called fossiliferous 

 greenstone, however, Avould perhaps be most correctly called a 

 '■' diabase tufa," as shown both by analysis and microscopic ex- 

 amination. 



Whatever may be the proper technical term for the class of rock 

 of which the Gympie crystalline diorite is a typical example, the fact 

 remains that throughout the whole extent of the great Devonian area 

 of Queensland no portion has yet been found to include auriferous 

 veinstones which will pay to work, where trappean disturbance of 

 this character is not present. 



At the Boyne the Devonian slates are cut at various angles by 

 dykes of hard crystalline diorite ; and for the most part the auriferous 

 quartz-veins are found at the absolute intersection of the two. The 

 very intelligent manager of the Boyne Company's leased ground had 

 found this fact verified in all the mining operations conducted 

 there. 



At Calliope intersecting dykes of serpentine, or diorite, are the 

 surest guides to the richest vein- stones, the Devonian slates and lime- 

 stones being the rocks intersected. 



At Crocodile, Blackfellows, and Morinish diggings, in the Eock- 

 hampton district, the conditions are analogous to those of the Boyne, 



