C PROCEEDIlS^eS OF THE GEOLO&ICi.L SOCIETY. [vol. Ixxvil, 



researches of Dr. Hume and his colleagues have shown that we 

 must now look elsewhere than in Egj^pt. 



The Peeside^'t said that the interesting and instructive dis- 

 cussion had left two doubts in his mind still unsatisfied. One was 

 whether two distinct problems, the origin of rift- valleys and the 

 origin of the Red-Sea depression, had not been confused. The 

 magnitude of the Eed-Sea depression was of so different an order 

 from that of the African rift-vallej^s, that any similar riftino-, 

 which may have taken place, would be of subsidiar}^ importance 

 in deterinining the position and form of the Red Sea. The other 

 doubt was as to the existence of anything which could properly 

 be called the Grreat Rift-Yalley. There was in Africa a 

 belt of country in which the surface-form known as a ' rift- 

 valley ' was of fairly frequent occurrence ; but it seemed to him 

 that there was insufficient evidence of continuity between them, 

 or of the existence of one continuous rift-vallej'. It appeared more 

 likely that further investigation would prove the independence of 

 the individual depressions, which should rather be regarded as 

 separate members of a continuous range or series. 



Dr. W. F. Hume, in reply, thanked Col. Lyons for his remarks, 

 and pointed out that Dr. Blanckenhorn had never himself visited the 

 Red-Sea region, the faults inserted having no basis of observation. 

 With regret it had to be stated that Dr. Blanckenhorn was fre- 

 quently incorrect in regard to the existence of faults in Eo-vpt. 

 He had bordered the Fayum with faults and then removed them, 

 shown an important one at Moghara Oasis which could not be 

 confirmed, and finally bordered the Red Sea with faults where 

 proof of their existence was absolutely wanting. 



Prof. Gregory was certainly justified in stating that the actual 

 diagram exhibited was a true fault ; but, if continued, it passed 

 into a monoclinal fold. The point did not aft'ect the main issue, 

 as the section was within the area of admitted fracture. 



Instead of assuming all the depressions discussed as part of 

 a great rift system, each had to be considered on its merits. 

 The parallelism of the Red-Sea borders could be explained as due 

 to erosion of a broad fold, and, apart from the apjDarent absence of 

 faulting on the large scale along its borders, the breadth of that 

 sea was such as to make it m.ost difficult to conceive it as a 

 tension-crack. In the Clysmic-Grulf area, which was narrower, 

 and lying between hill-masses of granite or limestones, folding 

 and fracture were intensely marked, but might well be due to 

 compression. The features on Avhich special attention would have 

 to be concentrated in connexion with rift questions were the rela- 

 tively narrow valleys of the Jordan, the Dead- Sea depression, and 

 those of South-Eastern Sinai, for which no simple erosion theory 

 seemed satisfactory. They were undoubtedly, like the Clysmic 

 Grulf, fault- guided or fault-controlled depressions. 



The speaker, as a result of his own studies, agreed with 

 Mr. Lamplugh that a dogmatic assertion of rifts at this stage 



