We have seen how man gradually brought to perfection the tools and weapons which were at first so clumsy. The growth of industry led to the birth of commerce, or, to speak more accurately, to that of barter. From the time of the earliest migrations intercourse was begun, or rather was carried on, between the tribes, as they gradually dispersed, often travelling considerable distances from each other, and fresh proofs of these relations are continually brought to light as we become better acquainted with prehistoric times. The flints worked by the cave-men of Belgium, the fossil shells so numerous at Chaleux, in the Frontal and Nuton caves, at Thayngen on the frontier between Switzerland and Germany, in Italy, in the stations of anterior date to the _terremare_ beds, have been found the shells of the pearl oyster of the Indian Ocean, whilst in the caves of the south of France, such as the Madeleine, that of Cro-Magnon, Bize in Hérault, and Solutré on the banks of the Saône have been picked up the shells of Arctic marine mollusca. The cave-man of Gourdan was decked with shells from the Mediterranean, and the man of Mentone in his turn wore a head-dress made of Atlantic shells. Fossil shells were also much sought after; we have alluded to those from Champagne found in Belgium; others from the shell-marl of Touraine and Anjou had been taken into the caves of Périgord, whilst sea-urchins from the cretaceous strata of the south of France were found in a prehistoric station of Auvergne, and M. Massenat picked up at Laugerie-Basse two specimens of a species not met with anywhere but in the Eocene deposits of the isle of Wight. The Neolithic station of Champigny, near Paris, has yielded some objects from the Alps, and from Belgium, from the Vosges Mountains, and the Puy de Dôme. [Illustration: 75.] Picks, hammers, and mattocks made of stag-horn. In the caves of Périgord were also found fragments of hyaline quartz, which must have been brought from the Alps or the Pyrenees. In Brittany and in Marne flints foreign to these granite districts are numerous; and Dr. Prunières tells us that similar discoveries were made under the megalithic monuments of France, and that neither in the eroded limestone districts of Lozère, known locally as _les causses_, nor under the dolmens of Haute-Vienne, were found any but implements made of rock not native to the country.