36 THE COKKALES. Book I. 
heavy black scoriaceous rock, the high specific gravity of 
which, no doubt, is caused by the large proportion of the 
titanic iron it contains. The trachytic lava, on the other 
hand, occasionally appears in the condition of pumice, 
which it is quite common to see swimming in the Lake. 
A ride on horseback along the shore, either north or 
south of the landing-place, is full of interest and enjoy- 
ment. Trees and bushes follow the line of the sand beach 
some twenty paces distant from the water's edge, so that 
the greater part of the ride can be made in the shade, 
while the eye passes over the Lake, resting there on the 
long chain of mountains separating Nicaragua from Upper 
Mosquitia ; here, on the twin cones of Ometepe, on the 
wooded hill of Zapotera, or on the eastern slope of the 
Mombacho and the group of the Corrales, situated at its 
base. 
This cluster of several hundreds of little islands, sepa- 
rated from the mainland as well as from each other by a 
most intricate system of narrow channels, is apparently 
the production of a stream of lava ejected from the crater 
of the Mombacho, and which, flowing down its eastern side 
and reaching the Lake, has been violently burst and 
cracked into so many islands by sudden cooling in the 
water, by which it was only half covered. The rock of 
which they are composed is a basaltic lava, of a somewhat 
scoriaceous character, at least in some sections of the whole 
mass. These little rocky islands are overgrown with the 
most magnificent trees ; the branches often meeting over 
the narrow channels between them, forming dark vaults 
through which the canoes of the Indian inhabitants of this 
diminutive archipelago find their way in a labyrinth of 
passages. Many of the islands are inhabited, each of 
them, in general, only by one family. But they are so 
