from twenty five to seventy nine miles per day, the mean rate being about thirty miles. The length of its whole course is about four thousand miles. As it skirts the coast of Guiana, it is increased by the influx of the waters of the Amazon and Orinoco, and by their junction acquires accelerated velocity. After passing the island of Trinadad, it expands, and is almost lost in the Caribbean Sea; but there appears to be a general movement of that sea towards the Mexican Gulph, which discharges the most powerful of all currents through the Straits of Florida, where the waters run in the northern part with a velocity of five miles an hour, having a breadth of from thirty five to fifty miles. {25} The temperature of the Gulph of Mexico is 86° in summer, or 6° higher than that of the ocean in the same parallel (25° N. lat.) and a large proportion of this warmth is retained, even where the stream reaches the 43° N. lat. After issuing from the Straits of Florida, the current runs in a northerly direction to Cape Hatteras, in North Carolina, about 35° N. lat. where it is more than seventy miles broad, and still moves at the same rate of seventy five miles per day. In about 40° N. lat. it is turned more towards the Atlantic by the extensive banks of Nantucket and St. George, which are from two hundred to three hundred feet beneath the surface of the sea; a clear proof that the current exceeds that depth. On arriving near the Azores, the stream widens and overflows, as it were forming a large expanse of warm water in the centre of the north Atlantic, over a space of two or three hundred miles from north to south, and having a temperature of from 8° to 10° Fahr. above the surrounding ocean. The whole area covered by the gulph water is estimated by Rennell at two thousand miles in length, and at a mean, three hundred and fifty miles in breadth, an area more extensive than that of the Mediterranean. The warm water has been sometimes known to reach the Bay of Biscay, still retaining five degrees of temperature above that of the adjoining ocean; and a branch of the gulf current drifts fruits, plants, and wood, the produce of America and the West Indies, to the shores of Ireland and the Hebrides. {26} From the above statements, observes Mr. Lyell, we may understand why Rennell has characterised some of the principal currents as oceanic rivers, which he describes as being from fifty to two hundred and fifty miles in breadth, and having a rapidity exceeding that of the largest navigable rivers of the continent, and so deep as to be sometimes obstructed and occasionally turned aside by banks, the tops of which do not rise within forty, fifty, or even one hundred fathoms of the surface of the sea.