in St. Michael’s Mount in Cornwail. 439 
filled with nearly the same gangue as the others: but the 
gangue of the last is continuous and uninterrupted ; while 
it cuts that of the preceding, and hence their comparative 
dates are known. The same is observed in all the znter- 
sections of veins, which in this country are very numerous.” 
That situation of the veins themselves certifies the re- 
peated catastrophes of the strata, by the successive fissures 
in which they were produced. 
On the manner in which the veins were formed, which 
is here the main point, on which M. Werner and myself 
agreed against the Huttonian theory, the subject begins at 
p- 448, of which the following is an abstract: ‘¢ It was in 
the side of this valley that M. Werner pointed out to me 
the principal phenomena which had convinced him that 
the veins were fissures filled up with substances precipitated 
against doth"sides of the space thus opened: this phzeno- 
menon is precisely the same which had led me also to that 
opinion.—In all veins, these new snbstances have been de- 
posited in symmetrical layers on both sides; and the in- 
terval between tiiem having been gradually narrowed by 
their accumulation, they have at last united towards the 
middle, where however there still remain some vacancies 
lined with small crystals. —Now in the small veins just de- 
scribed, M. Werner showed me a remarkable circumstance, 
which at once proves the symmetrical accumulation of the 
substances on the opposite sides of the fissures, and the 
catastrophes undergone by the veins themselves after having 
received their first gangue. These fissures have been evi- 
dently enlarged by a new subsidence of the strata, more 
considerable on one side than on the other, which has di- 
ae the first gangue in many places along the Jine of its 
rst junction. Now, the same operation has been recom- 
menced on both sides of the new fissure thus produced, and 
symmetrical layers uniting incompletely towards the mid- 
dle, have again been formed in the same manner as before.”” 
Mr. Allan could not be informed of the above observa- 
tions which T had made with M. Werner himself. But, 
sir, if he reads this letter in your Journal, { hope he will 
change the opinion he entertained of me with respect to 
accuracy in observations. 
I have the honour to be, sir, 
‘ Your obedient servant, 
Windsor, December 1, 1813. J. A. De Luc. 
Ee4 LXXIV. An 
