V

As we proceeded through this maze of stone-shadowed twilight we stopped at all available apertures to study interiors and investigate entrance possibilities. Some were above our reach, whilst others led only into ice-choked ruins as unroofed and barren as the rampart on the hill.

One, though spacious and inviting, opened on a seemingly bottomless abyss without visible means of descent. Now and then we had a chance to study the petrified wood of a surviving shutter, and were impressed by the fabulous antiquity implied in the still discernible grain. These things had come from Mesozoic gymnosperms and conifers⁠—especially Cretaceous cycads⁠—and from fan palms and early angiosperms of plainly Tertiary date. Nothing definitely later than the Pliocene could be discovered.

In the placing of these shutters⁠—whose edges showed the former presence of queer and long-vanished hinges⁠—usage seemed to be varied⁠—some being on the outer and some on the inner side of the deep embrasures. They