310 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [April 24, 



schists crop out at the foot of the range on the north side of the 

 creek, and granite on the point of the spur constituting the south 

 bank. 



" But I believe that the little quantity of gold found here has 

 travelled down the creek from the tract of greenstone above, and 

 that the whole of the gold has been derived from the latter rock. 

 No quartz fragments are to be seen on the surface, and scarcely any 

 are ever found in the drift constituting the wash-dirt." 



In the Jermyn-Street Museum a fine example of gold in diorite, 

 from the Woods Point District in Victoria, where similar conditions 

 obtain, is open for inspection. 



Although these instances have been pointed out to show the 

 absolute presence of gold throughout the mass of certain eruptive 

 trap-dykes, it is by no means our intention to assert that the noble 

 metal will be often found in siiificient concentration in this form to 

 become a source of supply in any material degree. 



In my opinion, however, these four groups of trappean rocks are 

 very important as indicative of the period at which the gold was 

 deposited in the veins of quartz, calc-spar, pyrites &c. which are 

 found at and near their intersection with Palseozoic and Metamorphic 

 strata, as well as in the trap-rocks themselves. 



The study of these peculiar vein- stones has led me to the con- 

 clusion that the fractures which they occupy were due partly to the 

 bursting power of the elastic vapours preceding the welling up of 

 the viscid trap into a portion of these rents, and partly to the con- 

 traction in cooling and crystalHzation of the intruded mass itself. 



The vein-stones themselves are probably deposits of mineral matter 

 from the hydrothermal action ivliicli preceded, ivas contemjyoraneous 

 tvith, and continued long after the traj) itself had cooled doivn. 



This action was similar to that of the Steamboat Springs in 

 America, cited by Blake and John Arthur Phillips. 



This may have been, and doutbless was, supplemented by infil- 

 tration from the trap-rocks themselves, the calc-spar element, so 

 characteristic of this class of lode, being probably supplied from 

 this source ; for, as a rule, the sparry portion of the ore is poorest 

 in gold. 



An exception to this rule is exemplified in a specimen previously 

 alluded to from the Caledonian Reef, Gympie, where the gold is 

 seen traversing calc-spar and quartz indiff'erently, the quartz crystals 

 being quite isolated in a menstruum of the spar. Again, in another 

 specimen it will be seen that in a breccia-lode where angular 

 fragments of quartz are cemented by carbonate of lime and brown 

 oxide of iron, the gold affects quartz, lime, and iron without respect 

 to affinities. Another shows a nugget of gold and carbonate of 

 bismuth, a portion of which, treated with hydrochloric acid, proved 

 that miich of the gold was isolated from the larger portion, as if the 

 bismuth and gold had been originally precipitated together. 



The very nature of the veins shows that they never can have 

 been subjected to any heat sufficient to cause fusion, but are due 

 entireljr to aqueous action. 



