OS 
GEOLOGY OE THE PEAK. 
cilhe * 111 like manner the lava of Scala, with which the 
city of .Naples is paved, contains a close mixture of basalt, 
nephcluie, and leucite. With respect to this last substance, 
^ inch lias liitherto been observed only at Vesuvius and in 
. ® environs of Home, it exists perhaps at the peak of Tene- 
lifie, m the old currents ot lava now covered bv more 
recent ejections. Vesuvius, during a long series of years 
lias also thrown out lavas without leueites : and if it be true, 
as M. von Bucli has rendered very probable, that these 
crystals arc formed only in the currents which flow either 
irom the crater itself, or very near its brink, we must not be 
surprised at not finding them in the lavas of the peak. 
lie latter almost all proceed from lateral eruptions, and con- 
sequently have been exposed to an enormous pressure in the 
interior of the volcano. 
In the plain of ltetaina, the basaltic lavas disappear under 
lieajis ot ashes, and pumice-stone reduced to powder. Thence 
to too summit, from 1,500 to 1,900 toises in height, the vol- 
cano exhibits only vitreous lava with bases of pitch-stonot 
and obsidian. These lavas, destitute of ninphibole and 
mica, arc ol a blackish brown, often varying to the deepest 
olive green. They contain large crystal's of feldspar, which 
are not fissured, and seldom vitreous. The analogy of those 
decidedly volcanic masses with the resinite porphyries! of 
tho valley of Tribisch in Saxony is very remarkable; but 
t he latter, which beloug to an extended and metalliferous 
formation of porphyry, often contain quartz, which is want- 
ing in the modern lavas. When the basis of the lavas of 
the Malpays changes from pitchstone to obsidian, its colour 
is paler and is mixed with gray ; in this ease, the feldspar 
passes by imperceptible gradations from tho common to the 
vitreous. Sometimes both varieties meet in the same frag- 
ment, as wo observed also in the trappean porphyries of the 
valley of Mexico. The feldsparry lavas of the' Peak, of a 
much Jess olack tinge than those of Arso in the island of 
This substance, which M. Dolomieu discovered ill the amygdaloids 
Catania m Sicily, and which accompanies the stilbites of Fassa in 
lyrol, forms, with the chabasie of HaUy, the genus Cubicit of Werner. 
M. Cordier found at reneriffe xeolite in au amygdaloid which Govers the 
basalts of La Punta di Naga. 
t Petrosilex resinite. Haiiy. 
1 Pechstein-porphyr. Werner. 
