PREHISTORIC SITES IN EGYPT— COLOUR VISION 291 



tufas and the Plateau Gravels of this phase yielded Acheulean tools and 

 flaking sites with Acheuleo-Levalloisean industry, and were eroded and 

 redistributed as Exogyra Gravels at lower levels. In decreasing rainfall, 

 with formation of another Wadi Tufa, pre-Sebilian settlements follow, and 

 the modern drainage system develops. As streams grew weaker, however, 

 narrow channels were cut in maturer valleys with Aterian sites on their 

 terraces. The region now became uninhabitable, and the Capsian and 

 Capso-Tardenoisean sites, in which primitive grinders and ostrich eggshell 

 beads occur, are on the Libyan Plateau. 



On the depression floor the ' fossil spring ' deposits discovered in 1931 

 yielded Acheulean, Aterian, and Capso-Tardenoisean sites. 



The explorers reject the fluviatile origin proposed by Dr. Collet for 

 Kharga and Dr. Sandford for the Faijoim ; they find no evidence for a 

 lake at any period in Kharga, but evidence for wind-borne and spring-borne 

 deposits. No dynastic remains were found prior to Twenty-seventh Dynasty, 

 and only one predynastic sherd, on the scarp ; probably because the Oasis 

 was already uninhabitable. Only under Persian rule did new hydraulic 

 skill reach artesian water and give Kharga a second cycle of prosperity. 



While Miss Caton-Thompson remains at home to prepare her materials 

 for publication Miss Gardner proposes to» continue her geological explora- 

 tion in the coming season. The Committee therefore asks to be reappointed, 

 with a further grant. 



COLOUR VISION. 



Final Report of Committee on Colour Vision (Prof. Sir Charles Sherrington, 

 Chairman ; Prof. H. E. Roaf, Secretary ; Dr. Mary Collins, 

 Dr. F. W. Edridge-Green, Prof. H. Hartridge, Dr. J. H. Shaxby). 



For testing individuals for defects of colour vision the most practical test is 

 some form of standardised lantern. The use of coloured lights is indicated 

 as the signals to be recognised in railway and marine work are always coloured 

 lights. 



Modifying (neutral) glasses should be used so that the lights can be seen 

 at different brightnesses. This is necessary, as some individuals with 

 defective colour vision recognise colours by their brightness. 



The colours used should be standardised spectrophotometrically, and 

 should include some limited to the extremes of the spectrum, so as to detect 

 persons with subnormal sensitivity to light, particularly of the red end of 

 the spectrum. 



Coloured traffic lights may be indistinguishable to colour-blind drivers. 

 By giving each coloured light a distinct shape, the colour-blind should be 

 able to judge by the shape. 



