452 Scientific Proceedings, Royal Dublin Society. 



prove to be auriferous, and in the light of our present knowledge 

 it would not be safe to exclude any geological series from the 

 possibility of being gold-bearing. Gold reveals its presence in 

 the earth's crust far less readily than other useful minerals, and 

 many a gold-field has been passed over by generations of men 

 before its riches were discovered. Hence the necessity for intelli- 

 gent search"; and the summary given in this remarkable work on 

 gold, p. 803, merits being cited. He says : — 



1st. " Gold exists in the oldest known rocks, and has been 

 thence distributed throughout all the strata derived from them. 



2nd. " In the metamorphosis of these derived rocks it has 

 been reconstructed in segregated quartz-veins by some process not 

 yet understood. 



3rd. " It is a constituent of fissure- veins of all geological ages, 

 where it has been deposited from hot chemical solutions, which 

 have leached deeply-buried rocks of various kinds, gathering from 

 them gold with other metallic minerals. 



4th. " By the erosion of strata containing auriferous veins- 

 segregated or fissure gold has been accumulated by mechanical 

 agents in placer deposits, economically the most important of all 

 the sources, of gold." 



He then passes in review the different formations from the 

 Laurentian upwards, and shows that gold has been found in con- 

 nection with them all, and points out the important role played 

 by the igneous rocks, (diorites, &c.) At p. 835 he cites the later 

 conclusions of Forbes as to the existence of two epochs of aurife- 

 rous impregnations throughout the world : — 



(1.) The Older or Granitic outburst. 



(2.) The Younger or Dioritic outburst. 



From the consideration of the facts brought forward by Lock, 

 and those continually appearing in the Journals specially dedi- 

 cated to mining and mineral matters, it may be concluded that 

 the search for gold need not necessarily be confined to any one 

 particular class of rock, and that the examination of any given 

 rock, chemically, is the only safe criterion by which to decide 

 whether it contains gold or not. Carefully executed chemical, 

 analyses or assays are, therefore, the only sure and safe guides in 

 the determination of the extent to which a rock or a district may 

 be considered auriferous and capable of leading to mining opera- 



