PREHISTORIC TOMBS OF EASTERN ALGERIA. 403 



vegetation, and that it supported a race, not numerous, however, which 

 cultivated the soil. (Monuments archeologiques 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 necrop- 

 olis 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 indi- 

 cates 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 im- 

 plements, scrapers and spear-heads. But for several thousand years, at 

 least from 5,000 to 10,000 years b. c, 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 tem- 

 perature 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 b. c, was 10 °C. Moreover, as the snail shells show- 

 ing 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 orna- 

 ments 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 in- 



