190 LA TOUCH E : GEOLOGY OF NORTHERN SHAN STATES. 



Five minutes' immersion in the solution was generally found to be 

 sufficient. 



Under the microscope thin sections of the ordinary massive 



„,.... . ± limestones, such as the two specimens from 



l v pica I dolomite. , . „ . ,„ 



• 1 near Yebin (D 3), Nos. 14/957 and 14/958, 



are seen to consist of a granular aggregate of minute dolomite crystals 



with irregular outlines, interlocking with each other (Plate 11, fig. 2). 



The individual crystals are usually clouded with brown semi-opaque 



matter, which is often concentrated in the centre, leaving a narrow clear 



zone round the edge. Where cavities are present the mineral filling 



them is clear, and frequently has a tendency, sometimes very pronounced, 



„ , .„ . to crystallise in idiomorphic rhombohedra. Any 



v eLiCitc veins 



calcite that the rock contains, as shown by stain- 

 ing with Lemberg's solution, is confined to fine cracks and veins, and 

 is evidently of secondary origin. This is well seen in No. 14/958. 



In the specimen No. 15/903 from near Baw (C 5), to the south 

 of Maymyo, the mass of the rock is of exactly 



Dolomitic limestone. . 



the same character as at Yebin, but it is 

 traversed by comparatively wide cracks filled with clear secondary 

 calcite, which accounts for the lower percentage of magnesium car- 

 bonate in this rock. 



In other cases also the lower percentage of carbonate of magnesia 

 is due to the brecciation of the original dolo- 



Breceiatcd dolomites. , 



mite ; and the re-cementmg of the fragments 

 in situ by a finely granular calcite paste. Staining with Lemberg's 

 solution makes this very clear in No. 15/900, from near Konghsa 

 bungalow on the Mandalay-Lashio cart road (F 2), where the 

 fragments are not acted upon, but the cementing material is dis- 

 tinctly stained. The cracks in this rock are filled partly with clear crys- 

 talline dolomite and partly with calcite. This rock also contains 

 minute grains of quartz, which account for the comparatively 

 high percentage of insoluble matter. In another specimen from 

 the same locality, No. 14/976, the original rock seems to have 

 been traversed by fissures which were then filled with a mixture 

 of calcite and dolomite, and afterwards crushed and re-cemented ; 

 for some of the clear fragments were evidently derived from veins, 

 and consist partly of calcite and partly of dolomite. No. 14/977, 

 from a cutting on the railway below Zebingyi, is also a brecciated 

 rock, but in this case the cementing material is entirely dolomitic^ 



