The latter contain no fewer than two hundred and twenty-six domes, seven rivers, eight cataracts, thirty two wells of unknown depth, and an immense lake which extends over six or seven leagues, the limit of which has never been reached by explorers.

I know these Kentucky grottoes, having visited them, as many thousands of tourists have done. The principal one will serve as a comparison to Back Cup. The roof of the former, like that of the latter, is supported by pillars of various lengths, which give it the appearance of a Gothic cathedral, with naves and aisles, though it lacks the architectural regularity of a religious edifice. The only difference is that whereas the roof of the Kentucky grotto is over four hundred feet high, that of Back Cup is not above two hundred and twenty at that part of it where the round hole through which issue the smoke and flames is situated.

Another peculiarity, and a very important one, that requires to be pointed out, is that whereas the majority of the grottoes referred to are easily accessible, and were therefore bound to be discovered some time or other, the same remark does not apply to Back Cup. Although it is marked on the map as an island forming part of the Bermuda group, how could any one imagine that it is hollow, that its rocky sides are only the walls of an enormous cavern? In order to make such a discovery it would be necessary to get inside, and to get inside a submarine apparatus similar to that of the Count d'Artigas would be necessary.

In my opinion this strange yachtsman's discovery of the tunnel by which he has been able to found this disquieting colony of Back Cup must have been due to pure chance.

Now I turn my attention to the lake and observe that it is a very small one, measuring not more than four hundred yards in circumference. It is, properly speaking, a lagoon, the rocky sides of which are perpendicular. It is large enough for the tug to work about in it, and holds enough water too, for it must be one hundred and twenty-five feet deep.

It goes without saying that this crypt, given its position and structure, belongs to the category of those which are due to the encroachments of the sea. It is at once of Neptunian and Plutonian origin, like the grottoes of Crozon and Morgate in the bay of Douarnenez in France, of Bonifacio on the Corsican coast, Thorgatten in Norway, the height of which is estimated at over three hundred feet, the catavaults of Greece, the grottoes of Gibraltar in Spain, and Tourana in Cochin China, whose carapace indicates that they are all the product of this dual geological labor.

The islet of Back Cup is in great part formed of calcareous rocks, which slope upwards gently from the lagoon towards the sides and are separated from each other by narrow beaches of fine sand. Thick layers of seaweed that have been swept through the tunnel by the tide and thrown up around the lake have been piled into heaps, some of which are dry and some still wet, but all of which exhale the strong odor of the briny ocean. This, however, is not the only combustible employed by the inhabitants of Back Cup, for I see an enormous store of coal that must have been brought by the schooner and the tug. But it is the incineration of masses of dried seaweed that causes the smoke vomited forth by the crater of the mountain.

Continuing my walk I perceive on the northern side of the lagoon the habitations of this colony of troglodytes--do they not merit the appellation? This part of the cavern, which is known as the Beehive, fully justifies its name, for it is honeycombed by cells excavated in the limestone rock and in which these human bees--or perhaps they should rather be called wasps--reside.

The lay of the cavern to the east is very different. Here hundreds of pillars of all shapes rise to the dome, and form a veritable forest of stone trees through the sinuous avenues of which one can thread one's way to the extreme limit of the place.

By counting the cells of the Beehive I calculate that Count d'Artigas' companions number from eighty to one hundred.