This discovery of what is now known as Chellean and Acheulean industry came through the explorations of Boucher de Perthes, between 1839 and 1846, in the valley of the River Somme, which flows through Amiens and Abbeville and empties into the English Channel half-way between Dieppe and Boulogne. In 1841 this founder of modern archæology unearthed near Abbeville a single flint, rudely fashioned into a cutting instrument, buried in river sand and associated with mammalian remains. This was followed by the collection of many other ancient weapons and implements, and in the year 1846 Boucher de Perthes published his first work, entitled _De l'Industrie primitive, ou des Arts à leur Origine_,(23) in which he announced that he had found human implements in beds unmistakably belonging to the age of the 'river-drift.' This work and the succeeding (1857), _Antiquités celtiques et antédiluviennes_,(24) were received with great scepticism until confirmed in 1853 by Rigollot's(25) discovery of the now famous 'river-drift' beds of St. Acheul, near Amiens. In the succeeding years the epoch-making work of Boucher de Perthes was welcomed and confirmed by leading British geologists and archæologists, Falconer, Prestwich, Evans, and others who visited the Somme. Lubbock's(26) article of 1862, on the _Evidence of the Antiquity of Man Afforded by the Physical Structure of the Somme Valley_, pointing out the great geologic age of the river sands and gravels and of the mammals which they contained, was followed by the discovery of similar flints in the 'river-drifts' of Suffolk and Kent, England, in the valley of the Thames near Dartford. Thus came the first positive proofs that certain types of stone implements were wide-spread geographically, and thus was afforded the means of comparing the age of one deposit with another. This led Sir John Lubbock(27) to divide the prehistoric period into four great epochs, in descending order as follows: The _Iron Age_, in which iron had superseded bronze for arms, axes, knives, etc., while bronze remained in common use for ornaments. The _Bronze Age_, in which bronze was used for arms and cutting instruments of all kinds. The later or polished Stone Age, termed by Lubbock the _Neolithic Period_, characterized by weapons and instruments made of flint and other kinds of stone, with no knowledge of any metal excepting gold. Age of the Drift, termed by Lubbock the _Palæolithic Period_, characterized by chipped or flaked implements of flint and other kinds of stone, and by the presence of the mammoth, the cave-bear, the woolly rhinoceros, and other extinct animals.