of some of the Principles of Vegetables into Bitumen , &c. 395 
But the water and vegetable matter must be regarded as extra- 
neous; and, if they are deducted, the real composition of the 
schistus is nearly as, follows. 
Silica - - 82.30 
Alumina - 12.61 
Oxide of iron - - 5 
99-9 
It evidently, therefore, belongs to the family of argillaceous 
schistus, although the proportion of silica is more considerable 
than has been found in those hitherto subjected to chemical 
analysis. 
This schistus has not been noticed by von Troil, nor by any 
of those who have written concerning Iceland ; for the slate 
which was sent to Professor Bergmann by the former, and which 
is mentioned by the latter in one of his letters, is there ex- 
pressly stated to be the common aluminous slate containing 
impressions.* 
§iv. 
From the experiments which have been related, we find that 
the leaves contained in the Iceland schistus, although they are 
apparently reduced almost to the state of charcoal, nevertheless 
retain some part of their original proximate principles, namely, 
extract and resin. This, of itself, is undoubtedly a remarkable 
# Letters on Iceland, by Uno von Troil, p. 355. 
Mr. Faujas St. Fond has however described a schistus nearly similar, which is 
found near Roche-Seauve, in the Vivarais, The stratum extends about two leagues ; 
and the only difference is, that, according to Mr. Sr. Fond, the schistus at Roche- 
Seauve is of the nature of marie, or, as he terms it, argillo-calcareous, whereas, this of 
Iceland is undoubtedly argillaceous. From Mr. St. Fond’s account, it does not appear 
that the vegetable leaves contained in the schistus of Roche-Seauve have been chemically 
examined. Essai de Geologic, par B. Faujas St. Fond, Tome I. pp. 128 and 134. 
