ten o'clock
It was impossible for Cyrus Harding and Ayrton , with these impediments , to make rapid progress . Moreover , the atmosphere was close , as if the oxygen had been partly burnt up , and had become unfit for respiration . At every hundred paces they were obliged to stop to take breath . It was therefore past ten o'clock when the engineer and his companion reached the crest of the enormous mass of rocks of basalt and porphyry which composed the north-west coast of the island . Ayrton and Cyrus Harding commenced the descent of this abrupt declivity , following almost step for step the difficult path which , during that stormy night , had led them to Dakkar Grotto . In open day the descent was less perilous , and , besides , the bed of ashes which covered the polished surface of the rock enabled them to make their footing more secure . The ridge at the end of the shore , about forty feet in height , was soon reached .