230 GRIESBACH: GEOLOGY OF THE CENTRAL HIMALAYAS. 



diately above the carboniferous limestone, shaly beds with coal-seams 

 and conglomerates and partly littoral, partly fresh-water conditions 

 prevailed in that area till late into Jurassic times. These disturb- 

 ances which are slightly indicated in the Himalayas are clearly 

 shown and occur on a larger scale in the West Central Asian area. 



The next great change in the Perso- Afghan area is the great 

 overlap of the upper cretaceous (hippuritic) limestone over the 

 neocomian, already alluded to. It has resulted in a great and often 

 strongly expressed unconformity. Again another and strongly 

 marked change occurs in the middle tertiaries of the Perso-Afghan 

 area. The purely marine miocene beds are overlaid, often with iso- 

 clinal bedding, at other localities distinctly unconformably, by upper 

 tertiary freshwater deposits. If the folding and crushing process 

 were alone the cause of these — shall I call them cycles of disturb- 

 ances — then at least some evidence of it should be observable 

 within the sequences of rocks as we see them. 



On the other hand, there is no direct evidence to show that the 

 raising of the Himalayas as a mountain system was in any way due 

 to these periodical fluctuations of sea-level, or as Suess terms it, 

 the "positive" and "negative" movements of the liquid covering of 

 the earth. The evidence of the transverse valleys in the Himalayas 

 points even to the probability that the raising up of the chains of hills 

 forming them, i.e., the folding and crumpling of its rock strata, must 

 have kept pace, step for step, with the erosion by rivers which we 

 now find traversing the whole width of this mountain system. 



Such transverse valleys, however, can only date since the last 

 of the periodical changes spoken of, i.e., since the middle tertiary 

 epoch. Before that time, up to the point when the last marine ter- 

 tiary deposits were laid down along the margin of the Himalayas, the 

 relative position of the Peninsular India and Central Asia must have 

 been the reverse of what we know them to be now, that is to say, the 

 surface of the Central Asian elevated massif must have been nearer 

 the centre of our earth than the surface of the continent, of which 

 the Peninsula of India forms only a portion of the remains. 

 ( 230 ) 



