PRESIDENTIAL ADDRESS — SECTION C. 121 



more numerous, more persistent, and larger in the Lower than 

 in the Upper Sihirian group. It has been observed that the 

 quartz contained in certain zones or belts of rock-bands is 

 auriferous, while that of adjacent and, apparently, litho- 

 logically similar belts is poor or barren, the detrital deposits 

 being rich or poor in gold according to their position in relation 

 to the respective zones. The geological evidence unmistak- 

 ably indicates an enormous amount of denudation, dating from 

 a,s far back as Upper Palaeozoic times, which has lowered the 

 surface of the Lower Palaeozoic rock-foundation by probably 

 thousands of feet. Over by far the greater portion of this 

 Lower Palaeozoic area there are no overlying deposits older 

 than Middle Tertiary, except a few occurrences of Devonian 

 and Mesozoic rocks. Any representatives of the great series 

 of rock-groups between Lower Palaeozoic and Tertiary have 

 been almost entirely removed from, if they ever existed at all 

 over, the main mountain-system of Victoria, and consequently 

 the Tertiary and Post-tertiary drifts may be regarded as the 

 concentrates which remain from the incalculable denudation 

 referred to. 



Naturally the gold disintegrated during that process re- 

 mained, while most of the material of the degraded rocks was 

 removed, and hence it came about that the Tertiary and Post- 

 tertiary drifts in the vicinity of the auriferous zones were found 

 to contain the detrital gold concentrated from the degradation 

 of mountains of Pala30zoic rock, and from the redistribution of 

 the various detrital deposits that had been successively accu- 

 mulated and removed in pre-tertiary times. 



It is no wonder therefore that the easily-accessible, shal- 

 low, and exceedinglj'-rich deposits of auriferous detritus were 

 speedily found and exhausted when the great prospecting 

 army spread itself over the land, and that the concentrates 

 of ages of Nature's work were in a few years appropriated by 

 man. 



As the rich shallow drifts became exhausted, the deeper 

 alluvial deposits were eagerly followed up wherever they were 

 found auriferous. Without any particular scientific guidance, 

 and after many blunders, the diggers found out that in nume- 

 rous localities the deepening channels containing the auriferous 

 diifts passed under layers of basalt, and thither they followed 

 them to depths of several hundreds of feet from the surface, 

 where powerful machinery became requisite and mining took 

 the place of mere digging. 



About the same time the gold-bearing quartz reefs out- 

 cropping on the ranges of exposed Silurian rock began to 

 attract attention, and the quartz-mining industry was quickly 

 developed. Nevertheless the annual yield of gold began visibly 

 to decrease ; alarm was experienced as to the probable utter 



