194 



LA TOUCHE : GEOLOGY OF NORTHERN SHAN STATES. 



bands of breccia re-cemented in situ that are sometimes met with ; 



thesa appear to have been formed while the limestone was being 



deposited, and are probably of the nature of a 'reef-talus'; but to 



the general brecciation of the formation as a whole. 



There seem to me to be two possible explanations of this 



. * . phenomenon. First, that the brecciation is 



Causes of pulverisation. _ , 1 



clue to the effect of an enormous stress, such 



as would be set up by the great earth movements that took place 



at the close of the Mesozoic period. That those movements had 



a profound effect upon the rocks of the whole area is shown by the 



violent folding that is exhibited by the sandstones and shales of 



the overlying Jurassic series (the Namyau beds), which are often 



vertical, and are usually inclined at high angles. On the other 



hand the Plateau Limestones are not, as a rule, thrown into steep 



folds, except among the Eastern Ranges, where they generally 



conform to the folding of the rocks beneath. Over the remainder 



of the area they are usually inclined at gentle angles, seldom 



exceeding 30 degrees, and are often horizontal ; but here and there 



a narrow band may be found in which they are violently contorted. 



It appears that, where the limestone was of great thickness, that 



is to say. over what is now the plateau proper, it was compelled 



to yield to pressure, not by folding in the ordinary way, but by 



faulting and by a general crushing of the formation as a whole. 



But there is another cause that may have produced this result, 



either bv itself or bv accentuating the effects 

 Settlement due to J . , ,. ,11, 



solution. of tectonic stresses, depending on the che- 



mical composition of the rock itself. Ever since 

 it was first formed, or at any rate since it was raised above the 

 level of the sea, it has been exposed to the dissolving action 

 of water containing carbonic acid in solution ; and the amount of 

 material that has been removed from the mass, judging by the 

 enormous quantities that even at the present day are being car- 

 ried off by the waters that percolate through the rocks and flow 

 away in the rivers, must bear a very considerable proportion to 

 its original bulk. The removal of this matter in solution results in 

 a general settling down of the whole mass, more accentuated in 

 those places where fissures allow a ready passage to the surface 

 waters ; and there is perhaps no more striking feature in the 

 scenery of the Shan plateau than the enormous number of cup- 

 shaped depressions, due to this cause, varying in width from mere 



