Birds of the cliffs, disturbed from long rest, wheeled and screamed about them, almost brushing their faces with long, fearless wings.

There was an occasional shelf where, with backs against the wall spotted with crystals of feldspar, they waited to breathe, hardly looking down from the dizzy ledge.

Great slabs of obsidian were piled about them between stretches of calcareous stone, and the soil which was like beds of old lava covered by thin layers of limestone, was everywhere pierced by sharp shoulders of stone lying in savage disarray.

Gradually rock-slides and rock-edges yielded a less insecure footing on the upper reaches, but the chasms widened and water dripping from lateral crevasses made the vague trail slippery and the occasional earth sodden and treacherous.

For a quarter of a mile their way lay over a kind of porous gravel into which their feet sank, and beyond at the summit of a ridge Jarvo halted and threw back to them a summary warning to prepare for "a long leap." A sharp angle of rock, jutting out, had been split down the middle by some ancient force--very likely a Paleozoic butterfly had brushed it with its wing--and the edges had been worn away in a treacherous slope to the very lip of the crumbling promontory.