National Geographic : 1898 Dec
ATLANTIC COAST TIDES short waves in the surf of the beach, with quick straight uprise of water in front and long gentle slope behind. In the north east, as in the shelf waters generally, rise and fall are of equal duration. BAY OF FUNDY TIDES A brief note follows on a region geographically intermediate between the estuaries and the shelf basins. These are of a special character, as was implied in the discus sion of the Gulf of Maine. It is not a typical estuary. The fact that its area is almost coextensive with the soft Triassic sand stones that appear in patches all about its shores, together with the fact that it is now rapidly cutting these remnants away, is perfectly compatible with the former existence of Triassic rocks through most of the area with an axial valley, narrower and more typical in form, through which the Petitcodiac, St John, and St Croix poured their waters into the Gulf of Maine. Given such conditions, the rushing tides resulting from the massive oscillation of the gulf waters into the estuary must have tended toward the present conditions.* A good description of the Fundy tides is still lacking. The greatest mean range is of 43.5 feet in the Basin of Minas, 50 feet at mean springs. Favoring meteorological conditions may in crease this by nearly one-half on rare occasions, so that a 70-foot tide is not incredible. It is found that narrowing bays multiply an accidental or non-lunar disturbance of water level in the same proportion that they do the tidal oscillation. Thus Geneva is situated at the head of a narrowing shoaling arm of the Lake of Geneva, perfectly comparable to the Bay of Fundy, with but a sixteenth the water volume of the whole lake. The seiches or swaying oscillations of the whole lake produce a wave two or three times as great at Geneva as at points anywhere in the main lake, for large oscillations or for small.t Similarly, barometric disturbances over the Gulf of St Law rence that cause only a slight change in the small local tide add six or seven feet to the 17-foot Quebec tide.+ During a storm which raged in Chesapeake bay in September, 1876, the water rose four feet two inches above mean high-tide level at Alexan *Similarly Delaware bay is believed to have been widened by the tide, though long shore action in the shallows outside is continuously striving to dam it off from the sea. t Forel, Le Leman, vol. ii, Seiches. t30 Jan., 189L, and 8 Feb., 1835. W . Bell. Dawson, Royal Soc. Can., 1895, vol. i, p. 26.