The cliff, as has been said, rose to a height of three hundred feet, but the mass was unbroken throughout, and even at its base, scarcely washed by the sea, it did not offer the smallest fissure which would serve as a dwelling.  It was a perpendicular wall of very hard granite, which even the waves had not worn away.  Towards the summit fluttered myriads of sea-fowl, and especially those of the web-footed species with long, flat, pointed beaks—­a clamorous tribe, bold in the presence of man, who probably for the first time thus invaded their domains.  Pencroft recognized the skua and other gulls among them, the voracious little sea-mew, which in great numbers nestled in the crevices of the granite.  A shot fired among this swarm would have killed a great number, but to fire a shot a gun was needed, and neither Pencroft nor Herbert had one; besides this, gulls and sea-mews are scarcely eatable, and even their eggs have a detestable taste.  However, Herbert, who had gone forward a little more to the left, soon came upon rocks covered with sea-weed, which, some hours later, would be hidden by the high tide.  On these rocks, in the midst of slippery wrack, abounded bivalve shell-fish, not to be despised by starving people.  Herbert called Pencroft, who ran up hastily.

“Here are mussels!” cried the sailor; “these will do instead of eggs!”

“They are not mussels,” replied Herbert, who was attentively examining the molluscs attached to the rocks; “they are lithodomes.”

“Are they good to eat?” asked Pencroft.

“Perfectly so.”

“Then let us eat some lithodomes.”

The sailor could rely upon Herbert; the young boy was well up in natural history, and always had had quite a passion for the science.  His father had encouraged him in it, by letting him attend the lectures of the best professors in Boston, who were very fond of the intelligent, industrious lad.  And his turn for natural history was, more than once in the course of time, of great use, and he was not mistaken in this instance.  These lithodomes were oblong shells, suspended in clusters and adhering very tightly to the rocks.  They belong to that species of molluscous perforators which excavate holes in the hardest stone; their shell is rounded at both ends, a feature which is not remarked in the common mussel.

Pencroft and Herbert made a good meal of the lithodomes, which were then half opened to the sun.  They ate them as oysters, and as they had a strong peppery taste, they were palatable without condiments of any sort.

Their hunger was thus appeased for the time, but not their thirst, which increased after eating these naturally-spiced molluscs.  They had then to find fresh water, and it was not likely that it would be wanting in such a capriciously uneven region.  Pencroft and Herbert, after having taken the precaution of collecting an ample supply of lithodomes, with which they filled their pockets and handkerchiefs, regained the foot of the cliff.