430 VOYAGE FROM INEADA, 
chap. To return, therefore, to the immediate purport 
> — , — 1 of our visit upon this occasion. The structure 
//rfcaa^ roc k, whereof the island consists, corre- 
sponds with the nature of the strata already 
described ; but the substances composing it 
were perhaps never before associated in any 
mineral aggregate. They all appear to have 
been more or less modified by fire, and to have 
been cemented during the boiling of a volcano. 
In the same mass may be observed fragments 
of various-coloured lava, of trap, of basalt, and 
of marble. In the fissures appear agate, chal- 
cedony, and quartz, but in friable and thin veins, 
not half an inch in thickness, deposited post- 
erior to the settling of the stratum. The agate 
appeared in a vein of considerable extent, 
occupying a deep fissure not more than an 
inch wide, and coated by a green earth, 
resembling some of the lavas of ^Elna, which 
have been decomposed by acidiferous vapours. 
Near the same vein we found a substance 
resembling native mercury, but in such ex- 
ceedingly minute particles, and in a crumbling- 
matrix, that it was impossible to preserve a 
specimen. The summit of this insular rock is 
the most favourable situation for surveying the 
mouth of the Canal : thus viewed, it has the 
appearance of a crater, whose broken sides 
were opened towards the Black Sea, and, by a 
