436 E. DAINTREE ON CERTAIN MODES OP 



During the so-called Miocene Tertiary epoch, however, intense 

 activity was again manifested, to he again renewed, after a period 

 of quiescence, during the so-called Pliocene Tertiary. 



Mr. Selwyn was of opinion that the gold was introduced into the 

 quartz veins of Yictoria at some period apparently between these 

 two epochs ; for, arguing on certain data developed in the Moorabool 

 valley, he says : " These particular drifts are clearly antecedent in 

 date to the upper and middle marine Miocene beds under which 

 they have now been traced. They do not contain gold in 'paying 

 quantity, the reason being that they are derived from the abrasion 

 of quartz veins that themselves contained little or no gold, and that 

 they were probably formed by forces in operation as long prior to 

 those which produced the gold-bearing veins, as the denudations 

 producing the Miocene gravels were prior to the Pliocene produc- 

 tive ones." 



Mr. Selwyn may be right with reference to the fresh introduction 

 of gold into the quartz veins during the periods he mentions ; but 

 the data on which he bases his evidence are hardly, I think, sufficient 

 to support the inference. 



These so-called " non-auriferous lower drifts of Yictoria," crop 

 out on the beach in Bass Straits, about a mile west of the Bird 

 Rock, south of Geelong, in exactly the same geological position as 

 those referred to by Mr. Selwyn on the Moorabool river, the cliff 

 sections showing the Lower Miocene clays and marls resting imme- 

 diately on them, full of marine fossils. 



They differ in one respect only from their representatives in the 

 Moorabool valley, that here they rest on the Mesozoic Carbonaceous 

 series of Yictoria, which is chiefly composed of grey sandstones and 

 shales, whilst in the Moorabool valley they rest on Silurian slates. 



They represent, however, near Bird Rock, no more the degrada- 

 tion of the strata on which they rest than do those of the Moorabool 

 valley ; they form part of a great marine drift, whose material was, 

 in my opinion, derived from the south ; and the further north we go 

 towards the higher levels, the more the whole middle Cainozoic 

 system thins out, until it ceases altogether, to be again met with in 

 the Murray basin at about a corresponding point above sea-level. 



What would seem to be the real reason why the lower and middle 

 Cainozoic rocks of Yictoria do not contain drift gold in paying quan- 

 tity, and the upper Cainozoic do, is that the one series is essentially 

 a marine drift ; the other is fluviatile, or, where auriferous, is essen- 

 tially so, consisting of the debris of rocks disintegrated by atmo- 

 spheric influence— arranged, sorted, and concentrated in continuous 

 water-sheds^ by fluvial action, the heaviest particles, such as the 

 gold, being in no case removed far from their original matrix. 



Undoubtedly auriferous quartz veins have been formed during the 

 Cainozoic period both in Hungary and at the Thames Diggings in 

 New Zealand ; but the veins there are, in both cases, in Plutonic 

 rock, or at or near the intersection of the Cainozoic strata with 

 Plutonic rock. 



Now in Australia at present no auriferous vein of any hind has 



