About two o’clock
With superhuman courage , the ascent was then resumed amid increasing dangers and difficulties . They were forced to bestride sharp peaks and leap over chasms so deep that they did not dare to look down them . In many places wooden crosses marked the scene of some great catastrophes . About two o'clock they came to an immense barren plain , without a sign of vegetation . The air was dry and the sky unclouded blue . At this elevation rain is unknown , and vapors only condense into snow or hail . Here and there peaks of porphyry or basalt pierced through the white winding-sheet like the bones of a skeleton ; and at intervals fragments of quartz or gneiss , loosened by the action of the air , fell down with a faint , dull sound , which in a denser atmosphere would have been almost imperceptible .