We have to look at a map to see the effect of these changes in the appearance of Europe; and there were no doubt other internal changes in the appearances of the countries themselves. The climate still was much more extreme than it is now. The glaciers were not yet quite gone. And the melting of these and of the winter snows gave rise to enormous rivers which flowed from every hill. Our little river the Ouse, for instance, which flows out through Norfolk into the Wash, was, when swollen by these means, probably many miles broad. Vast forests grew upon the banks of the rivers, and have left their traces in our peat formations; and in these forests roamed animals unknown to us. Of these the most notable was the mammoth (_Elephas primigenius_, in the language of the naturalists), a huge, maned elephant, whose skeleton and gigantic tusks are conspicuous in some of our museums, and who has given his name to this the earliest age of man’s existence: it is called the Mammoth Age of man. With the mammoth, too, lived other species of animals, which are either now extinct, or have since been driven from our latitudes; the woolly rhinoceros, the cave lion, the cave bear, the Lithuanian bison, the urus, the reindeer, and the musk-ox. It is with the remains of these animals, near the ancient banks of these great rivers, that we find the earliest tools and weapons manufactured by human hands. [Sidenote: Implements of the river drift.] The earliest of all the known remains of human-kind are the implements which are found deposited in the ancient beds of rivers. Now flooded by melting snow into huge lakes and now again drained off by the sudden bursting of a bound, it was natural that these great streams should often change their course, and often dig out huge areas of soil from the land upon their banks. In doing so they sometimes dug out the implements which earlier generations of men had left behind them on the surface of the soil, and which a few years would be enough to cover with mould and hide from sight. Then carrying along these implements of flint, they have deposited them in great beds of sand and gravel, somewhere in their ancient course.