FINAL SUMMARY: PETROLEUM. 73 



petroliferous marine series with the overlying fluviatile 

 deposits, and is attributable probably to the same cause. 



(**) At the commencement of a movement the tension produced 

 tends to be taken up equally by the anticlines and syn- 

 clines at regular intervals and more or less equal am- 

 plitudes. The anticlines, however, first come under denud- 

 ing influences and, as a result, yield more readily to the 

 lateral pressure than the synclines, in which deposition 

 is still proceeding. In other words there must always be 

 a tendency for anticlines to be a little sharper and 

 tighter than the intervening synclines. If the movement 

 commenced during the initial stages of deposition of the 

 sediments now forming these anticlines and synclines, 

 this characteristic would become much more strongly 

 marked, and it can be readily understood how the 

 continued movement would be expended in overfolding 

 and thrusting along these anticlinal lines of weakness 

 rather than in tightening the synclines. The long, very 

 flat, gentle, undisturbed synclines separating the tightly 

 compressed, overfolded and fold-faulted anticlines, in 

 Mesopotamia are more easily comprehensible on this 

 hypothesis. An apparent exception to this rule is to be 

 observed in the low, flat, very broad anticline, south-west 

 of the Jabal Nasaz, occurring in the region of tight anti- 

 clinal folds. This, to my mind however, is an exception 

 which merely illustrates the rule, for the anticline has 

 every appearance of having been recently initiated in the 

 midst of an unusually broad and flat syncline ; no doubt 

 as movement proceeds and denudation keeps pace with 

 it, the flexuring effect will become more and more localised 

 along the crestal area of the anticline and the latter more 

 compressed than the synclines on either flank. Through- 

 out the area covered by my survey, on the other hand, 

 no tight, compressed synclines were seen at all, the sub- 

 sidiary wrinkling in anticlinal flanks being on too minute 

 a scale to affect the question. 



There are indications in the Table Mountain area that the fold- 

 ing movement not only preceded the end of the Tertiary neriod but 

 also continued into the Recent period. {See Report No. 14, p. 65.) 



