IXXXIV PBOCEEDIIfGS OP THE GEOLOGICAL SOCIETY, 



forms as those wliich have been caused by the elevation and 

 fracture of strata." 



The next passage to which I wish to call your attention is the 

 description of the Sahara itself. M. Martins thus describes it. 

 " It is the examination of a dried-up sea-bottom to which the 

 reader is invited. Geologically speaking, this event is recent ; it 

 probably occurred a hundred thousand years ago. But although 

 we cannot tell the number of years, it has a relative date — it is 

 subsequent to the deposition of the Tertiary strata. When it 

 took place the Mediterranean already existed, for we find in the 

 Sahara the shells of the same Mollusca which still live on its 

 shores. The soil is impregnated with salt; it is formed of gypsum 

 or sulphate of lime, probably still deposited in existing seas, and 

 of sands brought down by the rivers which emptied themselves 

 into the Saharan gulf. Now these rivers lose themselves in the 

 desert, and their waters disappear by infiltration in the soil. Salt- 

 lakes, the level of which is some metres lower than that of the 

 Mediterranean, are the last remnants of this inland sea. A series 

 of these leads to the Grulf of the Gabes, the lesser Syrtis of the 

 ancients, on the shores of Tunis. The last of these salt-lakes, 

 the great lake of T'ejej, ceases only at 16 kilometres from the sea. 

 Were this isthmus broken through, the Sahara would again 

 become a sea, a Baltic of the Mediterranean." He goes on to 

 compare this with what is now going on in the Gulf of Bothnia, 

 the gradual elevation of the bottom of which will ultimately pro- 

 duce a Sahara between Sweden and Finland. 



But the disappearance of the Saharan sea took place without 

 any elevation of its bottom. While constant evaporation was 

 going on, the annual addition of water from the mountains was 

 but small ; but these torrents brought down enormous masses of 

 sand and clay and rolled pebbles, which accumulated at the mouth 

 of the Gulf in the Mediterranean, so that under the influence of the 

 then prevalent currents the opening became gradually narrower, 

 until a littoral cordon or strip of land, 16 kilometres wide, was 

 interposed between the Mediterranean and its Saharan gulf. No 

 longer in communication with the great sea, the rapid evapoi-ation 

 under an almost tropical sun soon reduced its waters below the 

 present level of the sea, and nothing remained but the salt-lakes 

 which still mark the eastern limit of the Saharan gulf 



Amongst tlie many discoveries of organic remains made during 

 the last twenty years, few have been more remarkable, both for 

 the number of specimens and the variety of genera and families, 

 than those of the mammalian and other remains at Pikermi in 

 Attica. The first discovery was made by Mr. George Finlay in 

 1835, and occasional researches have been made with greater or 

 less success in subsequent years. But it Avas not until M. Albert 

 Gaudry undertook a careful and systematic investigation of these 

 beds in 1855 and 1856, and again in 1860, that it was possible to 

 have even an approximative idea of the remarkable treasures of 

 organic remains contained in these Tertiary deposits of Pikermi. 



