The Gold Deposits of Mount Morgan, Queensland. 337 



be " theoretical," has not been discovered 3 although the 



mountain has been traversed by a number of adits and 

 cross-cuts, in addition to extensive surface excavations. 



In a second report, however, dated I )ecember i.2, 1 888,Mr. 

 Jack says, "The evidence nowon hand goes far to confirm my 

 original view that the auriferous material was deposited 

 by a thermal' spring." But it seems clear that if the 

 supposed evidences of deposition in the open air are found 

 to be fallacious, and we have merely an instance of the 

 deposition of auriferous material in a mass of shattered 

 rock by the agency of heated waters, these deposits, which 

 have been considered a remarkable instance of a most 

 unusual mode of occurrence of the precious metals, must 

 be relegated to the large class of ore deposits known to 

 have originated in the way just referred to, and of which 

 the Comstock Lode and other similar deposits are 

 examples. Recent developments, although showing the 

 supposed overflow deposit to be non-existent, and failing 

 to reveal any geyser pipe, have shown the ore body to be 

 confined to the upper portion of the mountain. 



Mr. Packard believes the history of the deposit to be as 

 follows : — 



" A period of dynamic disturbance is indicated by the 

 intrusion of dolerite, which, by extreme metamorphism 

 might have changed a dolomite into the serpentine we 

 now see; would have indurated the shales so that they 

 are scarcely to be distinguished from the crystalline rocks, 

 and would also, accompanied by chemical alteration, 

 change a ferruginous red sandstone into bluish-grey, 

 highly pyritiferous quartzite. Approaching the surface 

 the same energy would be expended in fracturing the 

 quartzite and greywacke, the intrusive dolerite would rise 

 through the fissures in the shattered rock, forming dykes, 

 which, meeting a silico feldspathic granular rock (the 

 gteywacke) would give it ;i semi-crystalline character. 

 The sandstone would similarly be vitrified. Later move- 



