SUMMIT OF THJ3 SILLA. 
431 
by the radiation of heat from the ground, and from the 
parenchyma of the leaves. The mercury was at 21 inches 
5'7 lines. We shaped our course direct to the eastern sum- 
mit. The obstruction caused by the vegetation gradually 
diminished; it Mas, however, necessary to cut down some 
heliconias ; but these arborescent plants were not now very 
thick or high. The peaks of the Silla themselves, as we 
have several times mentioned, are covered only with gramma 
and small shrubs of befaria. Their barrenness, however, is 
not owing to their height : the limit of trees in this region 
is four hundred toises higher; since, judging according to 
the analogy of other mountains, this limit would be found 
here only at a height of eighteen hundred toises. The 
absence of large trees on the two rocky summits of the 
Silla may be attributed to the aridity of the soil, the vio- 
lence of the winds blowing from the sea, and the conflagra- 
tions so frequent in all the mountains of the equinoctial 
region. 
To reach the eastern peak, which is the highest, it is 
necessary to approach as near as possible the great preci- 
pice which descends towards Caravalleda and the coast. The 
gneiss as far as this spot preserves its lamellar texture and 
its primitive direction; but where we climbed the summit 
of the Silla, we found it had passed into granite. Its tex- 
ture becomes granular; the mica, less frequent, is more 
unequally spread through the rock. Instead of garnets we 
met with a few solitary crystals of hornblende. It is, how- 
ever, not a syenite, but rather a granite of new formation. 
We were three quarters of an hour in reaching the summit 
of the pyramid. This part of the way is not dangerous, 
provided the traveller carefully examines the stability of 
each fragment of rock on which he places his foot. The 
granite superposed on the gneiss does not present a regular 
separation into beds: it is divided by clefts, which often 
cross one another at right angles. Prismatic blocks, one 
foot wide and twelve long, stand out from the ground 
obliquely, and appear on the edges of the precipice like 
enormous beams suspended over the abyss. 
Having arrived at the summit, we enjoyed, for a few 
minutes only, the serenity of the sky. The eye ranged 
over a vast extent of country : looking down fr> the north 
