158 FOR THE FLAG

situation and structure, belongs to the category of those
formed by the action of the sea. It is of both Neptunian
and Plutonic origin, like the grottoes of Crozon and
Morgate in the Bay of Douarneuez in France, of Bonifacio
on the Corsican coast; Thorgatten on the coast of
Norway, whose height is estimated at five hundred yards ;
the grottoes of Gibraltar in Spain, and Touranne in
Cochin China. In short, the nature of their dome-like
shells shows that they are the product of this double
geological travail.

The island of Backcup is largely formed of calcareous
rocks. From the steep banks of the lagoon these rocks
rise towards the walls in shelving slopes, leaving between
them a carpet of very fine sand, ornamented here and
there with tough yellowish clusters of samphire. From
great masses of seaweed and sargassum, the former very
dry, the latter wet, the acrid sca scent is exhaled, as the
tide, after having forced them through the tunnel, casts
them on the shores of the lagoon. But that is not the only
combustible employed in the multitudinous requirements
of Backcup, for I noticed an enormous stock of coal, which
must have been brought from the schooner by the tug.
But, I repeat, it is the burning of these masses of marine
matter, previously dried, that provides the fumes vomited.
by the crater.

Continuing my walk on the western side of the lagoon,
I discerned the habitations of this colony of troglodytes—
as I may surely call them? That part of the cave called
the Beehive fully justifies its name. There several rows