GEOLOGY. 



185 



steamers in passing, and from Rudmose Brown's 1 account, are 

 largely built up of granite rocks. 



(b) The Coastal Range. — The whole of the outer coast of the 

 district from the northern boundary for 110 miles south to the 

 mouth of the Tavoy river is a narrow belt of granite, interrupted 

 only by the entrance to the Heinze Basin and a few unimportant 

 streams. In the north, near Natkyizin and again at Kanbauk, 

 the intrusion broadens and bifurcates, throwing out a southward and 

 a northward pointing lobe, with narrow fingers of the Mergui 

 sedimentaries running up valleys and partially dividing them 

 from the main mass. The two lobes stretch out towards each 

 other along a line parallel to the long axis of the main intrusion 

 and probably mark a subsidiary axis of granite uprising. It would 

 appear that in the high hills to the north of the district where 

 Tavoy, Amherst and Siam meet, the Coastal and the Frontier 

 intrusions unite. 



(c) The Frontier Range. — This mass forms the high and con- 

 tinuous range of hills dividing Tavoy district from Siam. In the 

 north it is about twelve miles broad within British territory, but 

 narrows gradually as it is followed to the south-east, and also dim- 

 inishes in elevation. Up the valleys of the Kin chaung and the 

 Zinba chaung, two important tributaries joining the Tavoy river 

 in its upper reaches, Mergui sediments extend a long distance into 

 the heart of the intrusion, in the former case passing as a thin covering 

 sheet over the summit of the range. In several localities near 

 Sinbyudaing also, Merguis rise up the flanks of the granite core and 

 conceal the granite underlying the axis of the range. 



(d) The Central intrusion. — The Central intrusion or, more 

 correctly, group of intrusions, comprises two main areas of exposure, 

 and a large number of other cases where the granite appears through 

 the sedimentaries in outcrops of smaller size. The northern main 

 area, the Sinbo Sinma massif, is connected with the frontier intrusion 

 by a strip of granite which forms the high and rugged watershed 

 between the Heinze and Yebon chaungs and the Kamaungthwe ; 

 the boundaries here laid down are only an approximation owing 

 to the great natural difficulties of the country. Two lobes extend 

 south-eastward, the western of which, passing through Talaingya 

 reappears through the Merguis in minor inliers east of Kyaukanya, 



1 Scottish Geographical Magazine, Vol. XXIII, No. 0. 



