111.] LIFE IN THE OCEAN. 49 These the currents run less strongly from north to south. currents have had an important influence on the shape of the coast, as we shall see when we have to speak of that subject. It is partly owing to them that the east coast line of India is so straight as it is seen to be on the map, and that, as a consequence, it is so devoid of good harbours for ships. The sea is the home of myriads of animals; some of these, like fishes, swim freely through it; others, like crabs, prawns, and the creatures that produce shells, (of which the common little cowrie is probably familiar to all of my readers,) creep over the bottom; and others again, like corals, live firmly fixed to the bottom, almost like trees and plants, but are nevertheless true animals. These all breathe the air which is dissolved in water; and the waves of the sea, caused by the winds, are the agents by which the air becomes so dissolved. There are also vast quantities of plants living in the ocean; some growing on the bottom like land plants, others floating freely in its waters. They differ, however, from land plants in this particular, viz., that even those which are attached to the bottom are only attached, not nourished as most land plants are in part, through roots buried in the ground. They derive their nourishment from the water which bathes their surface. They are very varied in both colour and form, but on the whole brown is their prevailing tint. In certain parts of the ocean, as for instance in the North Atlantic to the south of the Azores, are vast permanent banks of a floating sea-weed termed the Sargasso, inhabited by myriads of fishes and other small animals. Such banks are found only in spaces of the ocean not traversed by strong currents. We have learned in this chapter that the sea is a vast body of salt water, in some parts very deep, deeper than the loftiest mountains that tower above its surface, and constantly kept in motion by the action of the tides, the winds, and its own heating and cooling; that the tides of the sea are low waves of vast extent produced by the attraction of the moon and the sun; and at full moon and new moon, the B.G. E 50 SUMMARY [CHAP. two sets of tidal waves coincide and produce the highest and lowest tides, called spring tides; while at the moon's quarters, when the high water of the lunar tides coincides with the low water of the solar tides, and vice versa, the rise and fall of the tide is least, producing neap tides. The rise and fall is increased where the sea is shallow, and becomes greatest in shallow bays and the mouths of large rivers; sometimes becoming so piled up as to produce a bore. The permanent currents are due partly to the winds and partly to the heating of the water in the tropics and its cooling in the polar regions; and these, by carrying heated water towards polar regions on the one hand, and cold water towards tropical regions on the other hand, exert an important influence on the climate of neighbouring regions. We have learned further, that the sea is constantly wearing away the edges of the land, and that the material thus carried away is spread abroad on the sea bottom; while almost the only addition it makes to the dry land is that of certain small islands, formed by the coral animal and its remains. It has a living less varied and It is the home Lastly, that the ocean is no desert to life. world of its own, different indeed, but not abundant than that which tenants the land. of the whale, the bulkiest of living animals, whose structure is as complex as that of the elephant or the camel; and on. the other hand, of myriads of minute creatures, whose very existence is only to be detected by employing the most powerful aids afforded by the optician's art; while others are so simple in structure that, though endowed with the power of moving and of taking food, they appear to be little mobile masses of jelly with no permanent distinction of parts. The vegetable life of the ocean, again, though equally abundant, is much less varied; and, with a few unimportant exceptions, its forms belong to that section of the vegetable kingdom which ranks lowest in the scale, viz. plants which produce no flowers. In the preceding chapter we learned that the surface of the sea is always giving off vapour under the heat of the sun, 111.] SUMMARY 51 which is carried away by the winds and eventually forms clouds and rain; that owing to the slowness with which the sea water becomes heated and cooled, there is much less difference in its warmth in the day and in the night, or in summer and winter, than there is in the case of the land: hence islands and places on the sea coast have a mild climate, never so hot or so cold as places under the same latitude in the interior of continents. Where warm currents like the Gulf Stream of the North Atlantic prevail, bringing warm water into a colder region, they help to make the climate warmer and more genial, and it may be added that cold currents flowing towards the equator on the other hand, by cooling the air, make the climate more rigorous than it would otherwise be. Such, for instance, is the case of Labrador in North America. CHAPTER IV. HOW ROCKS ARE FORMED. If the reader has appreciated the spirit of the teaching of the previous chapters; if he has clearly apprehended the great fact that the atmosphere, rivers, and sea waves are all slowly working a change on the outline and surface of the land; he will no longer look upon the existence of continents, islands, mountains, and plains, as dry ultimate facts, respecting which, when he has learned their positions and names, there is little more that it concerns him to know; but he will see that every single feature of the surface, every river-channel, hill and plain, every detail of the form of a coast line, must have a history of its own, stretching back, it may be, into an unfathomable past; and that each of these is the result of a vast number of causes, many of which he may see in operation around him. They are then no mere poetic fancies, but simple scientific truths, that are embodied in the words of Tennyson : "There rolls the deep where grew the tree. The hills are shadows, and they flow Like clouds they shape themselves and go." Bu our present business is not only with the broad fact that these things are changing and have always been chang CHAP. IV.] ORIGIN OF THE BENGAL PLAINS. 53 ing; we have to learn in what way and by what causes they have become what they are; and we shall find that, though there is no written chronicle to appeal to, to tell us their past history, still, by noticing their forms and structure, and by examining the materials of which they are built up, very much may be learned with almost the same degree of certainty, as if we had witnessed the whole process from the beginning. Let us see first of all of what materials the land is made; and let us start with the plains of Bengal. The surface soil alone will not tell us much. It is generally a mixture of fine sand and clay with decayed animal and vegetable matter, termed loam, and as we learned in the Introduction, it is very much like the silt or fine sediment that settles from muddy river water when it is allowed to stand till it becomes clear. But when a new tank is dug to a depth of 20 or 30 feet, the newly exposed earth slope will generally be found to exhibit layers of different kinds of earth. It may be that the first 6 or 8 feet from the surface, perhaps more, is a layer of loam like that seen at the surface; then perhaps comes a layer or bed of stiff clay; next, it may be, a layer or bed of sand; and very often, at a depth of about 20 or 30 feet, comes a thin layer of black-looking material, which, if it be dried and then thrust into a fire, will be found to lose all its blackness, and in great part will be burnt away. Such a layer is found almost everywhere in and about Calcutta, and in many parts of the 24-Pergunnahs and Jessore. It chiefly consists of the decayed remains of plants, and is sometimes spoken of as peat. But very often in this dark layer or peat bed (as it is termed by geologists) and below it, are found unmistakeable stumps of trees, with the roots attached, exactly in the position in which they grew, but now buried perhaps twenty or thirty feet below the surface; at such a depth indeed, that if all the layers above them could be removed over the whole surface of the country, the sea water would come up and actually cover them. The annexed woodcut represents the beds thus actually met with in excavating the large tank near the Sealdah railway station in Calcutta the |