That would be Nature's last struggle to enable them to breathe the diminishing atmosphere.

These, of course, were the last descendants of the fittest to breathe it; this was their temple, I suppose, and here they came to die--I wonder how many thousand years ago--perishing of heat, and cold, and hunger, and thirst; the last tragedy of a race, which, after all, must have been something like ourselves." "It's just too awful for words," said Zaidie.

"Shall we go into the temple?
That seems one of the entrances up there, only I don't like walking over all those bones." "I don't suppose they'll mind if we do," replied Redgrave, "only we mustn't go far in.

It may be full of cross passages and mazes, and we might never get out.

Our lamps won't be much use in there, you know, for there's no air.