island of geactosa. 
36 
researches of Sir James Hall on the influence of pressure 
in fusions, the existence of carbonic acid in substances con- 
tained in basalt presents nothing surprising. Several lavas 
of Vesuvius present similar phenomena. In Lombardy, 
between Vicenza and Albano, where the calcareous stone of 
the Jura contains great masses of basalt, I have seen the 
latter enter into effervescence with the acids wherever it 
touches the calcareous rock. 
AVe had not time to roach the summit of a hill verv re- 
markable for having its base formed of banks of clay under 
strata of basalt, like a mountain in Saxony, called the 
Scheibenbcrgen Hiigel, which is become celebrated on ac- 
count of the disputes of volcanean and neptunean geolo- 
gists. These basalts were covered with a mammiform 
substance, which I vainly sought on the Peak of Teneriffe, 
and which is known by the names of volcanic glass, glass of 
Muller, or hyalite : it is the transition from the opal to the 
chalcedony. AVe struck off with difficulty some fine speci- 
mens, leaving masses that were eight or ten inches square 
untouched. I never saw in Europe such fine hyalites as I 
found in the island of Gracio3a, and on the rock of por- 
phyry called cl JPeiiol de lot Banos, on the bank of the lake 
of Mexico. 
Two kinds of sand cover the shore; one is black and 
basaltic, the other wdiite and quartzose. In a place exposed 
to the rays of the sun, the first raised the thermometer to 
51-2“ (41° E.) and the second to 40° (32° E.) The tem- 
perature of the air in tho shade was 27'7° or 7'5°. higher 
than that of the air over the sea. The quartzose sand con- 
tains fragments of feldspar. It is thrown back by tbe water, 
and forms, in some sort, on the surface of the rocks, small 
islets on which seaweed vegetates. Fragments of granite 
have been observed at Teneriffe; tbe island of Gomora, 
from the details furnished me by M. Broussonnet, con- 
tains a nucleus of micaceous schist: — the quartz dissemi- 
nated in the sand, which we found on the shore of Gra- 
ciosa, is a different substance from the lavas and the trap- 
pean porphyries so ultimately connected with volcanic pro- 
ductions. From these facts it seems to be evident that in 
the Canary Islands, as well as on the Andes of Quito, in 
Auvergne, in Greece, and throughout the greater part oi 
