resorted to as, perhaps, the best and readiest means of securing personal protection, not only from enemies but from the exigencies of a variable climate. When, however, caves and rock-shelters were no longer sufficient to accommodate the increasing families of these nomadic people, the surplus population would have to migrate to localities which might not possess these natural means of shelter. In these circumstances, necessity would compel them to seek or invent some other means of security, the particular form of which would largely depend on the physical conditions of the environment. If stones were abundant they might be used to construct primitive huts, but if these materials failed, their next resource would probably be to dig a circular trench in the earth and to cover it with a timber roof and thatch. If, however, the locality was swampy, or liable to be flooded, it cannot be said that their ingenuity would be greatly overtaxed if they invented the plan of laying cross-beams over a series of supporting piles, so as to raise the floor of the hut above the damp soil. Or, finally, they might construct a chamber entirely underground in imitation of the natural caves. All these methods were adopted by the Prehistoric people of Britain.
In glancing over the inhabited sites of the Neolithic and subsequent people, we find that natural caves were still resorted to, not only as hiding-places in times of danger, but
