The waters of some of the great rivers of the world have been carefully examined at different times, in order to form some idea of the amount of solid matter which they contain, both dissolved and suspended; and the results are extremely important and interesting, for they enable us to form definite conclusions with regard to their capacity for transport. This subject has been investigated with great skill by eminent men of science. The problem is a very complicated one; but it is easy to see that if we know roughly the number of gallons of water annually discharged into the sea by a big river, and the average amount of solid matter contained in such a gallon of water, we have the means of calculating, by a simple process of multiplication, the amount of solid matter annually brought down to the sea by that river. But we must also add the amount of sand, gravel, and stones pushed along its bed. This may be roughly estimated and allowed for. These are some of the results: The amount of solid matter discharged every year by that great river, the Mississippi, if piled up on a single square mile of the bed of the sea,--say, in the Gulf of Mexico, where that river discharges itself,--would make a great square-shaped pile 268 feet high. But the Gulf Stream, sweeping through this gulf, carries the materials for many and many a mile away; so that in course of time it gradually sinks and spreads itself as a fine film or layer over part of the great Atlantic Ocean. The mud brought down by the great river Amazon spreads so far into the Atlantic Ocean as to discolour the water even at a distance of three hundred miles. The Ganges and the Brahmapootra, flowing into the Bay of Bengal, discharge every year into that part of the Indian Ocean 6,368,000,000 cubic feet of solid matter. This material would in one year raise a space of fifteen square miles one foot in height. The weight of mud, etc., that these rivers bring down is sixty times that of the Great Pyramid of Egypt, or about six million tons. Or, to put the matter in another way, if a fleet of more than eighty "Indiamen," each with a cargo of fourteen hundred tons of solid matter, sailed down every hour, night and day, for four months, and discharged their burdens into the waters of the Indian Ocean, they would only do what the mighty Ganges does quietly and easily in the four months of the flood season. It is probable that even the Thames, a small river compared to those just mentioned, manages to bring down, in one way or another, fourteen million cubic feet of solid matter. These few figures may suffice to give the reader some idea of the enormous amount of rock-forming materials brought down to the seas at the present day.