On the globe, says Michelet, water prevails, land is the exception, notwithstanding which, it is by no means easy to estimate the superficial extent of the sea. The slow changes of the firm land, which rises or sinks, the waves, which are inces santly at work diminishing the rocky shores, the banks of madrepores and polypes, which daily rise higher and higher from the bosom of the sea — all these causes constantly modify the slope of conti nents and cause perpetual alterations in the form of our globe. It has been, however, clearly ascertained that the sea covers two thirds of the surface of the globe, hence more than square miles are under water. The sea is, moreover, very unequally distributed, the Southern hemisphere being more abundantly provided with water than the Northern, so that the terrestrial globe may be roughly divided into two parts, one being looked upon as the world of the sea and the other of the dry land.