bare a passage for animals back and forth, yet soundings undertaken by the British government have established the fact, that the ocean deepens very gradually away from the shores of the mainland until a depth of six hundred feet is reached, when the shore falls away very suddenly. This is supposed to be the sea-coast of that time. The English Channel would then have existed as the valley of the Seine, and the Rhine have prolonged its flow over the present bed of the North Sea. As the land stood at this height through a large portion of the Glacial Age, it is not at all unreasonable to suppose that primitive tribes hunted back and forth along these valleys, and so doubtless many convincing proofs of their presence at that early day lie buried underneath the waves of the sea. In like manner, at the south, we know that elephants, lions, and hyenas passed freely from Africa to Spain, Italy, and the Island of Crete, and, consequently, the Mediterranean Sea must have been bridged in one or two places at least. The change from Pliocene times to early Glacial was so gradual that quite a number of animals lived on from one to the other, and, as we have already stated, one of these species has even survived to our own times. But we note the arrival in Europe of a great number of new animals, and the diversity of species seems at first an inexplicable riddle. The key, however, is to be found in the great climatic changes, which we have already mentioned as occurring during this age. On the one hand, we find such animals as the musk-sheep, reindeer, and arctic fox, animals whose natural home is in high northern latitudes, where snow and ice prevail 69 most of the year. Yet during this age they lived in Southern France and Italy, which must then have had a far different climate than that at present. Were we to confine our attention to these alone we would be convinced that the climate of Europe at that time was arctic in its severity. But side by side with the remains of these animals are found others which imply an altogether different climate. The hippopotamus, now frequenting the rivers of Africa, during that period roamed as far north as Yorkshire, England. This animal could not live in a country where the cold was severe enough to form ice on the rivers. The remains of a number of other animals are found whose natural home is in the warm regions of the earth. These two groups of animals, one from the north and one from the south, show how varied was the climate of Europe during the Glacial Age. In addition to these, there was also a large number of animals whose home is in the temperate regions of the earth--animals that thrive in neither extremes of heat and cold. This includes a great many animals of the deer kind, several varieties of bears and horses; in fact, the majority of those with which we are acquainted. Now, what conclusion follows from this assemblage of animals? Many theories have been put forward in explanation. It has been suggested that Europe at that time had a climate not unlike that of some portions of the earth at present; that is, a long and severe Winter was followed by a short but warm Summer. During the Winter reindeer and other northern animals would press from the north in search of food, but would retire on the approach of Spring, when their feeding grounds would 70 in turn be occupied by bisons and animals of a southern habitat. In confirmation of this view it is pointed out that a vast collection of bones, from the bottom of a sink-hole or pond in Derbyshire, England, conclusively show that in the summer-time it was visited by bisons with their calves, and in Winter by reindeer. This theory is open to a great many objections. As is well known, some animals make quite extensive migrations annually, but we can scarcely believe that heavy, unwieldy animals like the hippopotamus, were then such industrious travelers as to wander every year from Italy to Northern England and return. But the very ground on which this theory rests, that of strongly contrasted summers and winters, could not be true of Europe or the western portions of it, owing to the presence of the Atlantic Ocean, and the influence which it inevitably exerts on the climate. We see, then, that the presence of these different animals can be explained only by supposing great secular changes in climate. Let us see if we can strengthen this view by an appeal to the vegetation of this period. We have seen how important a guide as to climate were the remains of the vegetation of the early times. We therefore turn with more confidence to such discoveries as will tell us of the flora of this age. But there are many reasons why remains of plant growth should be few. As we shall soon learn, this was a period of flooded rivers; and in the gravels and loams thus formed is found our principal source of information as to the life of the age. But such a rush of waters would form gravelly banks or great beds of loam, and would sweep any plants which might be washed into its floods far out to sea; or if by chance they should become buried in such gravel beds, the action of water would speedily cause the decay of the tender portions, such as leaves, bark, and soft wood, in which case no profitable investigation could be made. Occasionally, however, around 71 the shores of old lakes, vegetable beds have been buried, and we know that some mineral springs deposit a sort of protecting sediment on every thing with which they come in contact. By such means, at rare intervals, leaves, seeds, and fruits have been sealed up for future inspection, and from a careful study of all such instances much valuable information has been obtained. At one place in the valley of the Seine was discovered, under a bed of tufa, the remains of a forest growth. It is not doubted that the deposit belongs to the Glacial Age. Yet the forest growth reminds us of that prevalent during the Miocene Age. The fig-tree, canary, laurel, and box-tree grew in profusion. These are all southern forms. One severe winter would kill them all, and even hard frosts would prevent the ripening of their fruits. Neither were the Summers hot and dry. This is shown by the presence of numerous plants which can not thrive in hot and dry localities, but live in the shady woods of Northern France and Germany. The evidence of this forest growth surely presents us an inviting picture of Europe during a portion of the Glacial Age. We are not without evidence, also, of a much more severe climate. In a lignite bed (a species of coal) found in nearly the same latitude as the forest growth just mentioned, we detect the presence of trees that grow only in cold northern climates, such as birch, mountain pine, larch, and spruce. And in some peat-bogs of Southern Europe belonging to this age are found willows now growing only in Spitzbergen, and some species of mosses that only thrive far to the north. It is quite evident that this deposit testifies to an altogether different climate from that indicated by the deposit before mentioned. No theory of migration can 72 explain this assemblage of plants, unless it be migration taking place very slowly, in consequence of an equally slow change of climate. From what we have just learned of the animals and plants living in Europe during this age, we can frame some conception of the different climatic conditions of Europe. On the one hand, we have a country with a mild and genial climate. Trees of a warm latitude were then growing as far north as Paris, and we may well suppose Europe to have abounded in shady forests and grassy plains, through which flowed large rivers. It was just such a country as that in which elephants and southern animals would flourish, while vast herds of deer and bovine animals wandered over the entire length and breadth of the land. Where animal life was so abundant there were sure to be carnivorous animals also, and lions, hyenas, tigers, and other animals added to the variety of animal life. This, however, is but one side of the picture. The other presents us with a very different scene; instead of an abundant forest growth, the land supported only dwarf birch, arctic willows, and stunted mosses. Arctic animals, such as musk-sheep and reindeer, lived all the year around in Southern France. The woolly mammoth lived in Spain and Italy. In short, the climate and conditions of life were vastly different in the two stages. We must now turn our attention to the proofs of glaciers in Europe, the phenomena from which this age derives its name. Descriptions of Alpine glaciers are common enough, but as glaciers and the Glacial Age have a great deal to do with the antiquity of man, we can not do better than to learn what we can of their formation, and their wonderful extension during this period. The school-boy knows that by pressure he gives his 73 snowball nearly the hardness of ice. He could make it really ice if he possessed sufficient strength. The fact is, then, that snow under the influence of pressure passes into the form of ice. In some cases nature does this on a large scale. Where mountains are sufficiently elevated to raise their heads above the snow line we know they are white all the year around with snow. What is not blown away, evaporated, or, as an avalanche, precipitated to lower heights, must accumulate from year to year. But the weight pressing on the lower portions of this snow-field must soon be considerable, and at length become so great, that the snow changes to the form of ice. But as ice it is no longer fixed and immovable. We need not stop to explain just how this ice-field moves, but the fact is that, though moving very slowly, it acts like a liquid body. It will steal away over any incline however small, down which water would flow. Like a river it fills the valleys leading down from the mountains. But, of course, the lower down it flows the higher the temperature it meets,
