864 Notices of Memoirs—W. H. Hudleston— 
has been so often made. When first this fissuring, or gaping of the 
rocks, occurred, there was a supply of molten silicates from below 
more than sufficient to fill up the void. But, as often happens in 
volcanic regions of modern date, the last stage of primary activity 
is represented by fissuring without injection of molten matter. A 
number of open cracks are thus formed, which favour the circulation 
of underground waters, often intensely heated, and not seldom pass- 
ing off as condensed steam where they happen to reach the surface. 
In Devonshire and Cornwall, the period when this phase was at. 
its height occurred most likely in late Permian and early Triassic 
times.! But, as every one knows, there have been many periods of 
shifting amongst the rocks; and doubtless the country must have 
participated in the great Tertiary earth-creep which folded the 
Downs and the Isle of Wight, about the same time that the Alps 
were being raised into a mountain-chain. Hach successive move- 
ment would be apt to produce modifications in the underground 
circulation, cramping it here and stimulating it there; and doubtless, 
as the temperature decreased, the solvent powers of the waters would 
diminish also. ; 
To such underground circulation in old volcanic districts like this, 
most of the phenomena in connection with metalliferous veins are 
due, though it must always be remembered that here we see a 
plutonic phase of what were volcanic activities at higher levels in 
earlier times. Fifty years ago De la Beche and the first Surveyors 
evinced an intense interest in this subject, and in the Memoir 
already referred to many hypotheses of origin are discussed. Since 
those days the world has been revolutionized in more ways than 
one, and in no way more than in the transfer of mining enterprise. 
But the experiences of the last five-and-twenty years in the Tertiary 
volcanic districts of North America have not been lost upon the 
numerous able men who have been employed as engineers or 
surveyors in those highly metalliferous regions. The late John 
Arthur Phillips left a record of his great knowledge and experience 
in his excellent treatise on Ore Deposits. And I have no doubt that 
many here are more or less acquainted with the important works of 
the French savant Daubrée, whose “ Etudes synthétiques de Géologie 
expérimentale,’ and “ Les eaux souterraines aux époques anciennes,” 
furnish us with an immense amount of information on the origin of 
metalliferous veins. 
Briefly, it may be said that the underground circulation theory is 
the one most generally adopted, the chief difference of opinion being 
as to the relative importance to be assigned to lateral secretion 
and to ascension respectively ; or, stated in simpler terms, whether 
1 Since the publication of portions of the address in the local papers, Mr. Thomas 
Collins, of Redruth, has written to say, ‘‘he considers there is evidence in the 
Tavistock district that the metalliferous deposits containing copper-ores had been 
formed in the Devonian rocks before the deposition of the main mass of the Carbon- 
iferous. The large copper-lodes of Mary Tavy, for instance, are in Devonian rocks, 
and cease altogether on coming into contact with the black schists of the Carbon- 
iferous.’’ It is suggested that this may be due to faulting at the junction. 
