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.