Then a remarkable change took place. The land began to sink, and its elevation so much decreased that the central part of the country became a huge lake, and the peak of Snowdon was an island surrounded by the sea which washed with its waves the lofty shoulder of the mountain. This is the reason why shells and shingle are found in high elevations. The Ice Age passed away and the climate became warmer. The Gulf Stream found its way to our shores, and the country was covered by a warm ocean having islands raising their heads above the surface. Sharks swam around, whose teeth we find now buried in beds of clay. The land continued to rise, and attracted by the sunshine and the more genial clime animals from the Continent wandered northwards, and with them came man. Caves, now high amongst the hills, but then on a level with the rivers, were his first abode, and contain many relics of his occupancy, together with the bones of extinct animals. The land appears to have risen, and the climate became colder. The sea worked its relentless way through the chalk hills on the south and gradually met the waves of the North Sea which flowed over the old Rhine valley. It widened also the narrow strait that severed the country from Ireland, and the outline and contour of the island began more nearly to resemble that with which we are now familiar. A vast period of time was necessary to accomplish all these immense changes; and it is impossible to speculate with any degree of certainty how long that period was, which transformed the icebound surface of our island to a land of verdure and wild forests. We must leave such conjectures and the more detailed accounts of the glacial and post-glacial periods to the geologists, as our present concern is limited to the study of the habits and condition of the men who roamed our fields and forests in prehistoric times. Although no page of history gives us any information concerning them, we can find out from the relics of arms and implements which the earth has preserved for us, what manner of men lived in the old cave dwellings, or constructed their rude huts, and lie buried beneath the vast barrows. The earliest race of men who inhabited our island was called the Palaeolithic race, from the fact that they used the most ancient form of stone implements. Traces of a still earlier race are said to have been discovered a few years ago on the chalk plateau of the North Down, near Sevenoaks. The flints have some slight hollows in them, as if caused by scraping, and denote that the users must have been of a very low condition of intelligence--able to use a tool but scarcely able to make one. This race has been called the Eolithic; but some antiquaries have thrown doubts upon their existence, and the discovery of these flints is too recent to allow us to speak of them with any degree of certainty. [Illustration: PALAEOLITHIC IMPLEMENTS]