Page:Popular Science Monthly Volume 16.djvu/162

148 Thénay to be of miocene date, or of Mr. Skertchly's from Brandon to be glacial. The accepted point is, that the men who made the ordinary flint implements of the drift lived in the Quaternary period characterized by the presence of the mammoth in our part of Europe. More than one geologist, however, has lately maintained that this Quaternary period was not of extreme antiquity. The problem is, at what distance from the present time the drift-gravels on the valley slopes can have been deposited by water-action up to one hundred feet or so above the present flood-levels? It does not seem the prevailing view among geologists that rivers on the same small scale as those at present occupying mere ditches in the wide valley-floors could have left these deposits on the hillsides at a time when they had not yet scooped out the valleys to within fifty or a hundred feet of their present depth. Indeed, such means are insufficient out of all proportion to the results, as a mere look down from the hill-tops into such valleys is enough to show. Geologists connect the deposit of the high drift-gravels with the subsidence and elevation of the land, and the powerful action of ice and water at the close of the Glacial age; and the term "Pluvial period" is often used to characterize this time of heavy rainfall and huge rivers. It was then that the rude stone implements of palæolithic man were imbedded in the drift-gravels with the remains of the mammoth and fossil rhinoceros, and we have to ask what events have taken place in these regions since? The earth's surface has been altered to bring the land and water to their present levels, the huge animals became extinct, the country was inhabited by the tribes whose relics belong to the neolithic or polished-stone age, and afterward the metal-using Keltic nations possessed the land, their arrival being fixed as previous to 400, the king of the Gauls then being called by the Romans by the name Brennus, which is simply the Keltic word for "king"—in modern Welsh brenin. To take in this succession of events geologists and archæologists generally hold that a long period is required. Yet there are some few who find room for them all in a comparatively short period. I will mention Principal Dawson, of Montreal, well known as a geologist in this Association, and who has shown his conviction of the soundness of his views by addressing them to the general public in a little volume, entitled "The Story of the Earth and Man." Having examined the gravels of St. Acheul, on the Somme, where M. Boucher de Perthes found his celebrated drift implements, it appeared to Dr. Dawson that, taking into account the probabilities of a different level of the land, a wooded condition of the country, and greater rainfall, and a glacial filling up of the Somme Valley with clay and stones subsequently cut out by running water, the gravels could scarcely be older than the Abbeville peat, and the age of this peat he estimates as perhaps less than four thousand years. Within this period Dr. Dawson includes a comparatively rapid subsidence of the land, with a partial reëlevation, which left large areas of the lower grounds beneath