Reviewn — BeadneU's Egyptian Oasis. 477 



movements have affected the shape of the ground by bringing rock- 

 masses of varying hardness and composition under the influence of 

 subaerial agents of destruction ; and thus deep and broad hollows in 

 the softer strata have been excavated nearly to sea-level out of 

 a plateau that rises in places to an elevation of 400 metres or more. 

 Changes in temperature have facilitated the crumbling of the rocks, 

 but the main agent in erosion is that of the sand-blast. 



The Kharga Oasis is described as one of the most windy places in 

 the country, and the sand which is drifted appears to be derived 

 mainly fro Qi strata newer than the Middle Eocene, which "are exposed 

 on the surface of the country between the Mediterranean Sea and 

 latitude 29° N." The sands are not wholly siliceous, but contain also 

 grains of white limestone. 



The extreme length of the Kharga Oasis is stated to be about 

 185 kilometres, or 115 miles, and the breadth to vary from 20 to 

 80 kilometres. 



Of particular interest is the evidence, obtained by the author, that 

 the depression had at an early period been the site of an immense lake. 

 He points out that thick deposits of calcareous tufa are found on the 

 escarpments bordering the oasis and on the face of the cliffs. " The 

 tufas frequently contain large numbers of freshwater shells and an 

 abundance of fossil vegetation, and, from the presence of casts of the 

 leaves of such trees as the oak, one is led to refer the deposit to the 

 more humid period which preceded the incoming of the modern desert 

 conditions." These tufas may have been formed on the margin of 

 the lake. 



The floor of the depression is occupied by large isolated patches of 

 "horizontal finely-bedded alternations of sand and clay, or more 

 frequently of an intimate mixture of the two ", lacustrine strata, 

 probably of Pleistocene age, which have been subjected to considerable 

 erosion. The discovery of fragments of pottery proves " that the 

 lake was contemporaneous with man ". It appears to have extended 

 over a distance of 136 kilometres, or 85 miles, and to have attained 

 a height of from 70 to 85 metres above sea-level. It probably 

 "existed well into the historic period", to about 500 e.g., but 

 "when the country became a Roman province, the lake had very 

 much contracted, and probably only existed as a marshy swamp 

 occupying the lower portions of the depression ". 



In the author's opinion there is good reason to believe that the 

 oasis was inhabited prior to the formation of the lake ; and he 

 remarks, "we must not forget the possibility that it was formed by 

 artificial means during one or other of the Egyptian dynasties between 

 3000 and 1000 e.g." Wells may then have been dug, and the 

 escape of water from a previously untapped artesian basin may 

 have been on a much larger scale than it is now ; or it is possible 

 that " If one or other of the porous beds, charged with water under 

 pressure, should, through the action of denudation on the overlying 

 beds, become exposed at the surface, the waters would escape through 

 natural springs in very large quantities ". Thus the higher water- 

 bearing strata, known as the ' surface-water sandstone ', may have 

 been covered by impervious clays, so as to contain water under 



