S50 
Mr Stodart cmd Mr Faraday 
in Auvergne opalized wood and opal-jasper in the pumicose 
conglomerates of Mont Dor and Mont du Cantal. It exists 
also in the pumice-conglomerates of the banks of the Rhine ; 
it occurs in the Euganean Mountains, in infiltrations in the 
perlite, and in the felspar rocks which belong to it : it exists 
equally in the Phlegrean plains; in the Pumice and Lipari 
Isles, and in the Island of Ischia. The Grecian Isles, Milo, 
Argentiera, Scorgot^a, and even Santorin, contain also a great 
quantity, which is found also in the conglomerates : of this I 
have satisfied myself, by examining the collections deposited at 
Freyberg by M. Hawkins. It appears, therefore, that this 
modification of the siliceous matter is peculiar to the trachytic 
formation, just as flint appears to be peculiar to the secondary 
calcareous, and jasper to primitive or transition rocks. It is 
thus that the different kinds of minerals appear to be confined 
each to a particular formation, which is one of* the most import- 
ant facts of geology 
Art. XXIV . — On the Alloys (^' Steel. By J. Stodart, Esq. 
F. R. S. ; and Mt'Faraday, Chemical Assistant to the Royal 
Institution -[•. 
A HE alloys of steel, made on a small scale in the laboratory 
of the Royal Institution, proving to be good, and the experi- 
ments having excited a very considerable degree of interest, 
both at home and abroad, gave encouragement to attempt the 
work on a more extended scale, and we have now the pleasure 
of stating, that alloys similar to those made in the Royal Insti- 
* From Beudant’s Travels. 
d*- From the Philosophical Transactions for 1829. Having already laid before 
our readers, in vol» iii. p. 308., an account of the early and very interesting experi- 
ments of Mr Stodart and Mr Faraday, on the Alloys of Steel with various metals, 
we avail ourselves of the earliest opportunity of printing the continuation of their 
valuable experiments. We attempted to make an abstract of this paper, but found 
the details too important to admit of any curtailment. 
Mr Stodart was so obliging as to favour us with specimens of several of these 
alloys for optical purposes, and though various plates of polished steel kept beside 
them for more than a year, were all affected with rust, yet not one of the alloys 
have suffered the least change. — Ed. 
