While the islands of sand referred to present many conditions favourable to commerce, fisheries, and other industries, their apparent durability is deceptive, and in some instances faith in their permanence has led to disastrous results. They owe their existence to the action of waves and currents, and unless blown sand is heaped upon them are raised but a few feet above mean sea-level, and are liable to inundation if a high tide is accompanied by an on-shore gale. A sad illustration of this plain conclusion is furnished by the disaster that overwhelmed the city of Galveston on the night of September 8, 1900, during which some 3,000 people perished and $20,000,000 to $30,000,000 worth of property was destroyed. This great loss was in large part due to the fact that the city was inundated by the advance over its site of the storm-driven waters of the Gulf of Mexico. The island on which Galveston stands (Fig. 9) was built by the waters of the Gulf, and during the hurricane referred to they again claimed their own. [Illustration: FIG. 9.--Coast of Texas.] Northward of Cape Cod, the rocks adjacent to the ocean are mostly hard and resistant, consisting largely of schist, gneiss, granite, trap, etc., which when undercut by the waves stand as bold cliffs and headlands. This portion of the continental border abounds in picturesque scenery and is abundantly supplied with fine harbours and well-sheltered havens in which boats may take refuge. Typical portions of this rugged coast are furnished by the magnificent sea-cliffs of Mount Desert and Grand Manan islands, the bold shores of Newfoundland and Labrador, and the precipitous border of Greenland. The scenery throughout nearly all of this vast extent of wave and storm beaten rocks is in striking contrast to the mild and generally monotonous sand-built shores to the south of Cape Cod. Between the angular headlands and rugged capes at the north, with their white girdles of surf, there are frequently curved beaches and numerous spits and bars of yellow sand which connect the salients of the shore or extend from them so as to furnish safe anchorages. On the arctic coast of North America the action of the waves and currents on the land is greatly retarded by ice, and the tides are small, but to what extent these conditions unfavourable to the work of the sea are counterbalanced by the abrasion performed by ice-floes is unknown. The northern border of Alaska, as well as the shore of Bering Sea, is mostly low and the rocks soft, although certain of the sea-capes are bold and are evidently composed of resistant material.