part 4] \ aiFT-VALLEi is westerh PERSIA. 249 



The succession of events here may he summarized as follows: — 



(1) Formation of a trough with gypsum-filling by partial collapse of the 



anticline. 

 (2 1 Levelling 1 of the gypsum surface and development of a stream across 



the position of the buried trough. 

 (3) The stream, cutting down through gypsum, discovers the faults, 



etches them out. develops subsequent* along them, and thus 



gradually eats out the gypsum filling the rift, until the present 



topography results. 



For the opportunity to make these observations, as well as for 

 permission to publish them, 1 am indebted to the Directors of the 

 Anglo-Persian Oil Company, to which I was temporarily attached 

 for duty while serving in the Mesopotamia Expeditionary Force. 



EXPLANATION OF PLATES XII XIV. 



Plate XII. 



View across the valley, ehowing escarpments of No. 1 fault, No. 3 fault, 

 and No. 4 fault. (See p.' 247.) 



Plate XIII. 



Gypsum-beds in contact with the limestone-wall. Gypsum on the right, 

 limestone on the left, (i^ee p. 217.) 



Plate XIV. 

 Slickensided rock-surface. (See p. 247.) 



Discussion. 



The President (Mr. Gr. W. Lamplugh), in asking Mr. Oldham 

 (who had read the paper) to convey the thanks of the Meeting 

 to the Author, commented on the numerous points of interest 

 illustrated by the paper. Not only did it describe an excellent 

 example of trough-faulting, but it showed also how easily fault- 

 features developed by erosion might be mistaken for surface- 

 exhibitions of faulting. We had still to discover what may he 

 the possible limits of surface-displacement by fault-movement. 

 In all the observed cases of recent faulting the displacement at any 

 one time was too slight to affect the general course of the drainage, 

 and this appears to have been the condition in the examples described 

 by the Author, on the presumption that the stream crossed the 

 anticline before the fault-movements had ceased. Physiographical 

 evidence usually indicates that even the higgest faults are of slow 

 growth. The existence of recent fault-scarps of great size is often 

 stated, but the evidence is mostly unconvincing. 



Sir JETHEO TEALL said that he had always thought that the 

 term 'rift-valley* implied a depression directly due to faulting. 

 But the Author had given strong reasons for believing that the 

 valley in question was not a rift-valle;j in this sense, and. there- 

 fore, the term, as used in the title appeared to be a misnomer. 



Prof. W. W. Watts enquired as to the state of mineralization 



