192 LA TOUCHE : GEOLOGY OF NORTHERN SHAN STATES. 



is dark, in others apparently crystalline, while in a few it appears 

 to be a minute foraminifer. It is interesting to note that these 

 organisms are the only ones that have escaped 

 £era UrV1Va ' ° " ,,ullim the general destruction of the shells of which 

 the limestone must have originally been composed. 

 This is in accordance with the observations of Dr. J. Murray and 

 Mr. R. Irvine, 1 who showed that when the shells of marine organisms 

 are subjected to disintegrating influences, those of the foraminifera are 

 the last to disappear. No. 14/983, from the south side of the Gokteik 

 gorge, near Nawnghkio (D 3), is also an oolitic limestone, but in this 

 case the oolitic granules are more sparsely scattered through the rock, 

 and consist of calcite, being stained with Lemberg's solution, while 

 the groundmass of the rock is the usual granular aggregate of 

 dolomite crystals (Plate 13, fig. 2). 



The specific gravities of these rocks, so far as they have been 

 determined, seem to form a rough, but fairly 

 Speci c ravitu ... consistent guide to the proportion of mag- 

 nesium carbonate that they contain ; the specific gravity of pure 

 dolomite being about 2 "90, while that of calcite is about 2 - 70. 

 Thus those specimens which have been shown by chemical analysis 

 to contain over 40 per cent, of magnesium carbonate have specific 

 gravities ranging from 2 - 793 to 2 "849, as shown in Table 7. In- 

 termediate varieties, with 25 to 33 per cent. McCO„, range from 

 2-717 to 2*833; and the pure limestones from the Permo-Carbon- 

 iferous beds give specific gravities ranging from 2-68 to 2*70. 

 A sufficiently large series of chemical analyses and accurate specific 

 gravities has not yet been made to enable one to come to any 

 definite conclusion on this connection, but 1 trust that one of my 

 colleagues will be able to take in hand a detailed study of these 

 limestones in the near future. 



The conclusions that we may legitimately draw from the enquiry so 

 far as it has aleady gone, correspond very closely, 

 I think, with those summarised by Prof. Skeats 

 in his paper on the dolomites of the Southern Tyrol (Op. tit., p. 138). 

 They may be stated thus :— 



(1) The inappreciable amount of insoluble residue is in favour 

 of the hypothesis that, the limestones were fo med under 

 conditions similar to those of modern coral reefs. 



i On Coral Beefs and other Carbcastje of Lime Formations in Modern Seas: 1'rc:. 

 Roy. Hoc. Edinburgh, Vol. XVII, p. 99. 



