]80 BKOWN & HERON: GEOLOGY AND ORE DEPOSITS OF TAVOV. 



at their maximum in this country of luxuriant vegetation and 

 excessive rainfall and it is almost impossible to find fresh rock except 

 in streams. Decomposition has penetrated to a remarkable depth 

 below surface, so much so that only a few exploration adits have 

 touched fresh rock. The first stage is the oxidation of the ferrous 

 constituent to ferric oxides and hydrates and the opening of the 

 close and irregular joint-planes, so that a red or brown rock is 

 produced, still hard, but breaking up into splinters. Passing 

 upwards, this is seen to soften and lose coherence until it becomes 

 a compact lithomarge, mottled in shades of brown, red and purple. 

 This varies considerably in thickness, depending on the slope of 

 the ground, being thin or absent on steep hillsides and thick on 

 flat land. It again in its turn is broken up by superficial creep and 

 the disintegrating action of tree roots, graduating, with the addi- 

 tion of a certain amount of organic vegetable matter, into the red 

 clayey soil of the surface. Laterite is found only on low-lying 

 flat land, where the subsoil is water-logged for most of the year, 

 such as bottoms of the broader valleys, where the streams have 

 little erosive power, but are not slow enough to deposit silt. In 

 these situations it is common, but attains only a moderate thickness, 

 three feet being about the maximum. 



The position of the Mergui Series in the geological scale is very 

 doubtful. No fossils have yet been found in 

 it. The Moulmein limestone is proved by its 

 fossils to be Carboniferous, and there is every reason to believe, 

 short of actual junction sections, that this formation overlies the 

 Merguis in the districts to the north and south. This would make 

 the latter pre-Carboniferous at least. Its general facies of great 

 thicknesses of uniformly argillaceous strata, with subordinate lime- 

 stones and quartzites, is suggestive of the Dharwars or the Transi- 

 tion (Pre-Cambrian) systems of the Himalayas, though the metamor- 

 phism of the Mergui Series is of lesser degree. 



Lithological similarity or state of metamorphism are of course 

 unreliable criteria in correlation, but we may say with fair probabi- 

 lity that the Merguis are Dharwarian (Archaean) or Transition (Pre- 

 Cambrian) in age, with a proviso that, in spite of the absence of 

 fossils, they may conceivably be as late as Older Palaeozoic. 



The correct designation for the fine-grained rocks is somewhat 



difficult to decide upon. Locally, amongst 



Argillites. ^ mining men f the district, they are always 



