108 
A DISPUTED CONJECTURE. 
buccinites, and otlier fossil marine productions. M. Cordiet 
brought away some of this tufa, which resembles that in 
the environs of Naples and Home, and contains fragments 
of reeds. At the Salvages, which islands La Perouse took 
at a distance for masses of scoria 1 , even fibrous gypsum is 
found. 
I had seen, while herborizing between the port of Orotava 
and the garden of La Paz, heaps of grayish calcareous stones, 
of an imperfect eonehoidal fracture, and analogous to that of 
Mount Jura and the Apennines. I was informed that these 
stones were extracted from a quarry near Kambla ; and that 
there were similar quarries near Kealejo, and the mountain of 
Boxas, above Adexa. This information led me into an error. 
As the coasts of Portugal consist of basalts covering calca- 
reous rocks containing shells, I imagined that a trappean 
formation, like that of the Yicentin in Lombardy, and of 
JLarutsh in Africa, might have extended from the banks of 
the Tagus and Cape St. Vincent as far as the Canary Islands ; 
and that the basalts of the Peak might perhaps conceal a 
secondary calcareous stone. These conjectures exposed me 
to severe animadversions from M. G. A. de Luc, who is 
of opinion that every volcanic island is only an accumula- 
tion of lavas and scorite. M. de Luc declares it is impossible 
that real lava should contain fragments of vegetable sub- 
stances. Our collections, however, contain pieces of trunks 
of palm-trees, enclosed and penetrated by tlie very liquid 
lava of the isle of Bourbon. 
Though Tenerilfe belongs to a group of islands of consi- 
derable extent, the Peak exhibits nevertheless all the charac- 
teristics of a mountain rising on a solitary islet. The lead 
finds no bottom at a little distance from the ports of Santa 
Cruz, Orotava, and Garachieo : in this respect it is like St. 
Helena. The ocean, as well as the continents, has its moun- 
tains and its plains ; and, if we except the Andes, volcanic 
cones are formed everywhere in the lower regions of the globe. 
As the Peak rises amid a system of basalts and old lava, 
and as the whole part which is visible above the surface of 
the waters exhibits burnt substances, it has been supposed 
that this immense pyramid is the effect of a progressive 
accumulation of lavas; or that it contains in its centre 
a nucleus of primitive rocks. Both of these suppositions 
