surrounding them, suggesting to the careful navigator the frequent use of the thermometer to test the temperature of the water where ice is likely to be encountered. They are seldom met with below the 40th parallel. Field-ice, covering a surface of many square miles, with a thickness of from ten to twenty feet, is frequently fallen in with off the coasts of Labrador and Newfoundland. Though less dangerous to navigation than the iceberg, it is often a serious obstruction. Vessels that incautiously run into a pack of ice of this kind, or have drifted into it, have often found themselves in a _maze_, and have been detained for weeks at a time, and not without some risk to their safety in heavy weather. * * * * * TIDAL WAVES.—Notwithstanding elaborate treatment of the subject by hydrographers, stories about ocean tidal waves are most frequently relegated by landsmen into the same category with tales of the great sea-serpent. Sailors, however, have no manner of doubt as to their existence and their force. During violent storms it has been noticed that ocean waves of more than average height succeed each other at intervals—some allege that every seventh wave towers above the rest. Be that as it may, there is no doubt that a sudden change of wind when the sea is strongly agitated frequently produces a wave of surpassing magnitude. Other causes, not so obvious, may bring about the same result, producing what in common parlance is called a “tidal wave.” This is quite different from the tidal wave proper, which periodically rushes up the estuaries of rivers like the Severn, the Solway, the Garonne, the Hoogly and the Amazon. In the upper inlets of the Bay of Fundy, where the spring-tides rise as high as seventy feet, the incoming tide rushes up over naked sands in the form of a perpendicular white-crested wave with great velocity. The tidal wave of the Severn comes up from the Bristol Channel in a “bore” nine feet high and with the speed of a race-horse, while the great bore of the Tsien-Tang-Kiang in China is said to advance up that river like a wall of water thirty feet in height, at the rate of twenty-five miles an hour, sweeping all before it.[33] The ocean tidal wave dwarfs these and all other waves by its huge size and tremendous energy. The effective pressure of such a wave being estimated at 6,000 pounds to the square foot, it is easy to understand how completely it becomes master of the situation when it topples over on the deck of a ship. Only once in the course of a good many voyages has the writer been an eye-witness of its tremendous force. The occasion was thus noticed in the New York papers of the 2nd and 3rd of August, 1896: