﻿324 Mr. D. Forbes' s Researches in 



results which closely approximate to the composition of the gold 

 from the Clogau mine in North Wales previously examined by 

 me, and which correspond to the formula Au 6 Ag, which by cal- 

 culation requires 90-88 per cent, gold to 9'12 per cent, silver. 



The geological age of the appearance of this gold is, I believe, 

 identical with that of the intrusion of the stanniferous and auri- 

 ferous granites of Cornwall, which appears to be some time be- 

 tween the Silurian and Carboniferous periods ; and it seems not 

 improbable that the greater portion of both, the stream- tin ore 

 as well as the native gold, was originally disseminated through- 

 out the mass of the granite itself, and subsequently, through 

 its disintegration, became set free and washed down into the 

 alluvial deposits formed by the rivers. 



Native Gold, Wicklow, Ireland. 



To the good offices of Mr. F. Jennings I am indebted for two 

 small nuggets of gold from the Wicklow alluvial deposits, which 

 have enabled me to determine their composition. 



The specimens were rounded irregular masses, and evidently 

 contained internal cavities, so that the determination of their 

 specific gravity is not to be relied upon. 



Their colour was a rather brassy golden hue, whilst the ex- 

 ternal surface of the gold was abraded and possessed a very 

 dingy lustre. 



The specific gravity of the one nugget was found to be 15*07, 

 whilst that of the other was only 14*34 — probably owing to the 

 existence of internal cavities or quartz particles. 



The analysis was conducted upon the first-mentioned of these 

 nuggets (spec. grav. 15*07), and in precisely the same manner 

 as described in the case of the gold from the Clogau mine in the 

 first part of these researches. 



The results obtained gave the following percentage compo- 

 sition : — 



Gold 91*01 



Silver 8*85 



Quartz .... 0*14 



100*00 

 These results do not coincide with the analysis of Mr. W. 

 Mallet, published in the Journal of the Geological Society of 

 Dublin, vol. iv. p. 271, but are almost identical with those ob- 

 tained by Mr. R. Scott, published in Sir W. Wilde's f Catalogue 

 of the Gold Antiquities in the Collection of the Royal Irish 

 Academy/ 1862, when the amount of iron obtained by him is 

 subtracted*. 



* Mr. Scott informs me that this was probably due to entangled pyrites, 

 and that he also found a trace of copper present. 



