Ch. XXXVIIL] eelative age of metals. 629 



derivative copper have been found near Wexford in the Devonian, 

 not far from points where mines of copper are worked in the Silurian 

 strata.* 



Although the precise age of such copper lodes cannot be defined; we 

 may safely affirm that they were either filled at the close of the Silurian 

 or commencement of the Devonian period. Besides copper, lead, and 

 silver, there is some gold in these ancient or primary metalliferous veins. 

 A few fragments also of tin found in Wicklow in the drift are supposed 

 to have been derived from veins of the same age.f 



Next, if we turn to Cornwall, we find there also the monuments of a 

 very analogous sequence of events. First the granite was formed ; then, 

 about the same period, veins of fine-grained granite, often tortuous (see 

 fig. 692., p. 569.), penetrating both the outer crust of granite and the 

 adjoining fossiliferous or primary rocks, including the coal-measures j 

 thirdly, elvans, holding their course straight through granite, granitic 

 veins, and fossiliferous slates; fourthly, veins of tin also containing 

 copper, the first of those eight systems of fissures of different ages already 

 alluded to, p. 621. Here, then, the tin lodes are newer than the elvans. 

 It has indeed been stated by some Cornish miners that the elvans are 

 in some few instances posterior to the oldest tin-bearing lodes, but the 

 observations of Sir H. de la Beche during the survey led him to an 

 opposite conclusion, and he has shown how the cases referred to in 

 corroboration can be otherwise interpreted.^ We may, therefore, assert 

 that the most ancient Cornish lodes are younger than the coal-measures 

 of that part of England, and it follows that they are of a much later 

 date than the Irish copper and lead of Wexford and some adjoining 

 counties. How much later it is not so easy to declare, although pro- 

 bably they are not newer than the beginning of the Permian period, as 

 no tin lodes have been discovered in any red sandstone of the Poikilitic 

 group, which overlies the coal in the south-west of England. 



There are lead veins in the Mendip hills which extend through the 

 mountain limestone into the Permian or Dolomitic conglomerate, and 

 others in Glamorganshire which enter the lias. Those worked near 

 Frome, in Somersetshire, have been traced into the Inferior Oolite. In 

 Bohemia, the rich veins of silver of Joachimsthal cut through basalt con- 

 taining olivine, which overlies tertiary lignite, in which are leaves of 

 dicotyledonous trees. This silver, therefore, is decidedly a tertiary for- 

 mation. In regard to the age of the gold of the Ural Mountains, in 

 Russia, which, dike that of California, is obtained chiefly from auriferous 

 alluvium, it occurs in veins of quartz in the schistose and granitic rocks 

 of that chain, and is supposed by MM. Murchison, De Verneuil, and Key- 

 serling to be newer than the syenitic granite of the Ural — perhaps of ter- 

 tiary date. They observe, that no gold has yet been found in the Per- 



* I am indebted to Sir H. de la Beche for this information. See also mapa 

 and sections of Irish Survey. 



f Sir H. de la Beche, MS. notes on Irish Survey. 

 t Report on Geology of Cornwall, p. 310. 



