In proof of the action here ascribed to the waters of the sea, in transporting materials to an unlimited extent, we may add the well known observation, that the stones brought up by the lead from the bottom of the sea, are generally round and polished, hardly ever sharp and angular. This could never happen to stones that were not subject to perpetual attrition. 373. Currents are no doubt the great agents in diffusing the detritus of the land over the bottom of the sea. These have been long known to exist; but it is only since the later improvements in navigation, that they have been understood to constitute a system of great permanence, regularity, and extent, connected with the trade winds, and other circumstances in the natural history of the globe. The Gulf stream was many years since observed to transport the water, and the temperature of the tropical regions into the climates of the north; and we are indebted to the researches of Major RENNELL, for the knowledge of a great system of currents, of which it is only a part. That geographer, who is so eminent for enriching the details of his science with the most interesting facts in history or in physics, has shown, that along the eastern coast of Africa, from about the mouth of the Red Sea, a current fifty leagues in breadth sets continually towards the south-west.[189] It doubles the Cape of Good Hope, runs from thence north-west, preserving on the whole the direction of the coast, but reaching so far into the ocean, that, about the parallel of St Helena, its breadth exceeds 1000 miles. From thence, as it approaches the line, its direction is more nearly east; and meeting in the parallel of 3° north, with a current which has come along the western coast of Africa from the north, the two united stretch across the Atlantic, in a line somewhat south of west, and in a very wide and rapid stream. This stream meets the American land at Cape St Roque, where it is joined by another coming up along the eastern shore of that continent, and directed towards the north. They proceed northward together till they enter the Gulf of Florida, from which being as it were reflected, they form the Gulf stream, passing along the coast of North America, and stretching across the Atlantic to the British Isles. From thence the current turns to the south, and, proceeding down the coast of Spain and Africa, meets the stream ascending from the south, as already described, and thus continues in perpetual circulation. The velocity of these currents is not less remarkable than their extent. At the Cape of Good Hope, the rate is thirty nautical miles in twenty four hours; in some places forty five; and under the line seventy seven. When the Gulf stream issues from the Straits of Bahama, it runs at the rate of four miles an hour, and proceeds to the distance of 1800 miles, before its velocity is reduced to half that quantity. In the parallel of 38°, near 1000 miles from the above strait, the water of the stream has been