10 Joseph LeConte—Genesis of Metalliferous Veins. 
transportation, sedimentation and reconsolidation, and yet we 
Study the process now going on as a type of what took place 
in earlier times. So also it may indeed possibly, though I 
think not probably, be true that we rarely see metals deposited 
from solfataric waters which have not been derived from pre- 
viously formed metalliferous veins, and yet none the less is the 
process in the two cases the same, and we rightly study the one 
to throw light on the other 
Finally, Dr. Sandberger regards the whole phenomena of 
me removes the subject forever from the clear light of induc- 
tive research where oe observers had hoped to place it, and 
remands it to the limbo of more or less probable conjecture. 
the ota of the process * which metalliferous veins were 
orme 
After this discussion, which we hope has served the purpose 
of placing the ascension-theory in clearer light, we return with 
increased confidence in our previously formed views, and will 
now proceed to apply them in the explanation of the phenom- 
ena of mineral vein 
1. Association with metamorphism.—lf metalliferous veins are 
formed by solfataric action, then we at once see why they are 
usually associated with the evidences of volcanic activity re- 
cent or past, and especially with metamorphism of the country 
rock: for solfatarie action is but the feeble remnant of preced- 
ing vulcanism, and metamorphism is undoubted] — by 
superheated water under heavy spoon and ch 
2, Absence of ee fit of solfataric action.—If metal] lifer- 
ous veins were formed by solfataric action, at the time they 
were forming, if alkaline sulphides predominated, white chalky 
siliceous residue of acid decomposition (as at Sulphur Bank), 
or, if alkaline carbonates predominated, siliceous sinter (as at 
Steamboat Springs), must have existed at the then surface. 
ut as such surface deposits are never more than 20 to 80 feet 
thick—they must, except in cases where the process is still go- 
ing on, have long ago been entirely swept away _by erosion, 
and therefore the deeper parts only, i.e. the trve veins exposed 
to view. In ordinary mineral veins we have the deeper de- 
posits revealed but the process of filling has been hitherto ob- 
secure. In solfataric springs on the other hand we have the 
