DEVONIAN SYSTEM i PLATEAU LIMESTONE, 



195 



' sink-holes ' of a few yards in diamete to broad valleys, several! 

 miles in length, which may be found in most places, but chiefly 

 along the crests of fault scarps or near the edges of the deep can- 

 yons in which the larger rivers flow (Plates 3, 4, and 5). The 

 continual settlement caused by this constant removal of the substance 

 of the rock does, I think, account satisfactorily for the universal 

 brecciation observed, and at the same time for the evidence, given 

 above, of a long continuance of the action ; and it is, perhaps, the 

 chief cause to which the general crushing of the limestone must be 

 attributed. 



The recrystallisation of the limestone as dolomite, described above, 

 is so universally developed, and has destroyed 



Destruction of organic itg originaI structure to such an extent, that it 

 remains. _ ° 



is exceedingly rare to find any trace of organio 

 remains still left in it. As a general rule such organisms as do occur 

 are confined to the upper part of the formation, which has not been 

 converted into dolomite, and is much more compact and less coarsely 

 crystallised than the lower ; but where the alteration is complete an 

 occasional ossicle of a crinoid stem, or the faintly visible ' dirt-band ' 

 outlining the septa or the circumference of what was once a coral 

 are all that can be detected, with, in a few cases, some very minute 

 foraminifera, only visible in thin sections under the microscope. 

 Throughout the whole of the continuous expanse of limestone, extending 

 from Maymyo to the Salween, with one notable exception, not a single 

 determinable fossil that could be seen with the unaided eye has been 

 found, though both my colleagues and I have examined thousands 

 of outcrops with the most minute care. So meagre is the evidence 

 of the existence of living organisms at this period, that one might 

 be tempted to speculate on a possible precipitation of the limestone 

 from the waters of an ocean saturated with carbonate of lime, if the 

 fact that the remains of organisms can occasionally be detected did 

 not at once prove that such a theory could not be maintained. 



This paucity of organic remains, together with the rarity of 



outcrops of more than a few square vards in 

 mS.° geneity ° f f ° r " area > the homogeneity of the whole formation, 



and the irregularity of the dislocations, whether 

 folds or faults, that have affected the rocks, render any attempt to 

 follow up definite horizons, or to establish any divisions within the for- 

 mation, a hopeless task. And yet it bridges over a period of conti- 

 nuous deposition of very considerable length, viz., that extending from 



o 2 



