The name of the Isles of Shoals is first mentioned by Christopher Levett in his narrative of 1623. The mariners of his day must have known of the description and the map of Smith, but they seem to have little affected the name he gave the islands. It would not be unreasonable to infer that the group was known by its present name even before it was seen by Smith, and that his claims were of little weight with those matter-of-fact fishermen. Some writers have made a difficulty of the meaning of the name, attributing it to the shoals, or schools, of fish seen there as everywhere along the coast at certain seasons of the year. East of the islands, toward the open sea, there is laid down on old charts of the Province an extensive shoal called Jeffrey's Ledge, named perhaps for one of the first inhabitants of the isles, and extending in the direction of the coast from the latitude of Cape Porpoise to the southward of the Shoals. On either side of this shallow, which is not of great breadth, are soundings in seventy fathoms, while on the ledge the lead brings up coarse sand in thirty, thirty-five, and forty-five fathoms. The presence of this reef tends to strengthen the theory that these islands, as well as the remarkable system of Casco Bay, once formed part of the main-land. The earlier navigators who approached the coast, cautiously feeling their way with the lead, soon after passing over this shoal came in sight of the islands, which, it is believed, served to mark its presence. Jeffrey's Ledge has been a fishing-ground of much resort for the islanders since its first discovery.[104] To whatever cause science may attribute the origin of the isles, I was struck, at first sight, with their resemblance to the bald peaks of a submerged volcano thrust upward out of the waters, the little harbor being its crater. The remarkable fissures traversing the crust of the several members of the group, in some cases nearly parallel with the shores, strengthens the impression. In winter, or during violent storms, the savagery of these rocks, exposed to the full fury of the Atlantic, and surrounded by an almost perpetual surf, is overwhelming. You can with difficulty believe the island on which you stand is not reeling beneath your feet.