1872.] DAINTEEE GEOLOGY OP QUEENSLAND. 301 



generally confined to pyritous diorite or diabase, whose percenta,ge 

 of silica rarely exceeds one half of their total constituents, another 

 typical intrusive rock appears to perform similar functions in the 

 more siliceous rocks of metamorphic districts, such as those of the 

 Cape River. 



Sometimes this partakes of the character of felspar porphyry, and 

 sometimes of a porphyrite. 



It is at the intersection of these acid-felspathic dykes with the 

 mica- and hornblende-schists, and in areas within the influence of 

 the said intrusions, that several of the auriferous veins round Mount 

 Remarkable, Mount Davenport, and Mount Elvan, in the Cape- 

 River Mining- district, are found. 



What the age of these metamorphic rocks relatively to the Devo- 

 nian system may be is uncertain, though it is probable that they maj' 

 represent the Lower Silurian series of Victoria, or the still older 

 metamorphic system of that colony. 



The richest copper lodes yet opened in Queensland, viz. " The 

 Peak Downs " and " Mount Perry," lie within such areas. Neither 

 of these seems to be in any way in contact with igneous dykes, but 

 to be true lodes. The former of them had, up to the 30th June, 

 1870, smelted 29,168 tons of ore for a yield of 5839 tons refined 

 copper, and had been proved, at the time of our visit at the end 

 of that year, to extend at the 40-fathom level 1500 feet in an east 

 and west strike, with an average width of 2 feet. The Mount 

 Perry, lately opened, with very favourable prospects, is bounded by 

 granite of metamorphic origin, very similar in character to that of 

 Ravenswood. 



In this last- mentioned gold-mining district nearly 200 distinct 

 reefs are now being actively worked, the yield, from 2120 tons of 

 the quartz first crushed from various claims, having been 5682 oz. 

 of smelted gold, or at the rate of 2 oz. 14 dwts. per ton*. 



There is no evidence of trappean action influencing the produc- 

 tion of the veins at Ravenswood ; or if there be, it is deep-seated ; 

 and there is, therefore, this practical difiference to be borne in mind 

 when considering the mode of occurrence of metallic minerals in 

 Queensland, viz. that in the fossiliferous palaeozoic equivalent of the 

 Devonian no case has yet been observed free from trappean dis- 

 turbance where paying quantities of metallic ore or metal have been 

 found, whilst in the metamorphic areas this has not been shown to 

 be an absolute necessity. That the stanniferous granites of the 

 Severn river, which are now yielding such marvellous quantities of 

 tin ore, are of metamorphic origin, seems clear from the description con- 

 tained in a private letter ju,st received by me from Mr. Aplin, lately 

 the Government Geologist for Southern Queensland, who says : — 



" The rock is a loosely aggregated, coarse-grained, highly mica- 

 ceous granite, abounding in thin threads and veins of quartz. It 

 seemed to me to be metamorphic, and was not in large bosses and 

 broad sheets, but in numerously jointed beds. 



* The total yield for 1871 from this gold-field, just received, gives 60,444 oz 

 of gold. 



