GEOLOGY. 



189 



tion products of the normal granite but injected into 

 fissures instead of remaining where they segregated. 



(c) Quartz veins, as a rule smaller than the pegmatites and 



consisting of quartz only. They arc probably the silica 

 residuum of the granite after the other minerals had 

 crystallised, and represent a stage in differentiation more 

 advanced than that of the pegmatites. 



(d) Basic intrusions. These are dykes of basic rock, in origin 



extraneous to the granite, localised in certain places — 

 for instance Danithagya in the extreme north of the 

 coast, near Kandaung, between Kyaungdaung-maw-gyi 

 and Mawshyi, and near Tavoy Point. They run irregu- 

 larly, and vary greatly in size, the largest observed, 

 an exceptionally wide one, being 20 feet across. Gener- 

 ally they are fine-grained and their minerals are much 

 altered and dilHcult to determine. Three slides from 

 Danithagya showed :— 



(1) A coarse aggregate of brown and green hornblende or 



biotite, a little sphene and apatite, in a ground-mass 

 of quartz and acid plagioclase. 



(2) Laths and clusters of hornblende in a finely crystalline 



ground-mass of plagioclase. 



(3) Coarse actinolite, yellowish mica and much olivine or white 



pyroxene, with grains of black iron ores. 



(4) Near Bok they appear to be basalts in which the augitc 



has been largely chloritised and the felspars replaced by 

 calcite and scaly decomposition products. Here they 

 traverse the Mergui argillites also, and probably do so 

 elsewhere, but this is the only point where Merguis are 

 exposed on the. shore, and on land they probably weather 

 so readily as to be easily missed. 

 Near Tavoy Point, the southernmost extremity of the Coastal 

 Range, three microscope sections examined gave : — 



(5) A fine-grained rock consisting of grains and rods of horn- 



blende, laths of felspar and epidote. 



(6) A similar rock with quartz instead of felspar. 



(7) Felspar phenocrysts in a ground-mass of plagioclase and 



indeterminate green rods, probably hornblende. 

 The above examples serve to show the somewhat heterogeneous 

 composition of the basic dykes ; unfortunately it was 



