Page:Popular Science Monthly Volume 58.djvu/411

Rh vegetation, and that it supported a race, not numerous, however, which cultivated the soil. (Monuments archéologiques du Sahara, 1881, Bull. Soc. d'Anthropologie, Paris.)

Strong confirmation of the view that decided climatic changes have taken place in eastern Algeria since the time when the Roknia necropolis was built, is afforded by the excavations of Dr. Borguignat in these dolmens. He found in the dolmens numerous shells of Helix aspersa, a large snail common in the gardens and fields of Europe. These shells were similar to those living in the damp and cool climate of Europe, while those actually living at Roknia offer features produced by the dry and hot climate of the present day. This sufficiently indicates a decided change of climate, which must have occurred certainly more than a thousand years before the time of Homer, or of the founding of Rome. We dug up some of these semi-fossil shells, and also found plenty of the recent ones on top of the soil within the dolmens.

Many authors attribute the dryness and sterile nature of the eastern lands to the removal of forests by man within historic periods, but this is a decided mistake. There has been a slow secular process of elevation, desiccation and consequent deforestation of the regions around the Mediterranean, which began to take place thousands of years before the founding of the ancient civilization of Egypt, Babylon and Assyria, at, if not before a time when neolithic culture gradually supplanted that of the race which used only rough, unpolished, unmounted flint implements, scrapers and spear-heads. But for several thousand years, at least from 5,000 to 10,000 years if not throughout the neolithic epoch, the scenic features and climate of Egypt, Libya and Algeria have remained unchanged.

Bourguignat claims that the climate indicated by the snails of the Roknia dolmens nearly corresponds to that of Paris, whose mean temperature at our time is 10°.1 C. (about 52° F.), while that of Roknia is 17°.5, being a difference of 7°.4.

Reasoning from these data and certain astronomical calculations, this author decides that the mean annual temperature of Roknia, at a period 2,200 years was 10 °C. Moreover, as the snail shells showing the influence of this cool, rainy climate were found in the lower beds of the sepulchral chambers, in the strata in contact with the human bones, he concludes that the megalithic monuments of Roknia extend back to that date. They are thus not less than about 4,000 years old, and thus it would appear that the bronze age of ancient Libya goes back that length of time.

This once decided, Dr. Bourguignat explained the presence of ornaments of bronze and gilded silver, which he supposed the inhabitants were unable to make themselves, to commercial exchange with the Egyptians and what he calls the people of Nigritia. The Kabyle