﻿448 ME. J. B. SCE1VEN0E ON THE [Aug. I9IO, 



generally speaking, being more abundant towards the centre. 

 Such bodies also show concentric structure. 



(3) Smaller bodies occur, sometimes, but not always, accompanied 

 by the larger cavities and bodies. They consist of tourmaline, of 

 corundum, and of both tourmaline and corundum. When both 

 minerals are present, the corundum forms a shell to a nucleus 

 of tourmaline. The corundum bodies frequently show concentric 

 structure. 



(4) The tourmaline-corundum rocks are associated with other 

 rocks which lead to the conclusion that the structures described 

 in the two immediately preceding paragraphs are the result of 

 replacement of the materials of pre-existing bodies at the time of 

 extensive granitic intrusions. 



(5) They are also associated with rocks which point to the 

 original beds having been laid down under conditions similar to 

 those that obtained when the Pahang Chert Series was deposited. 



(6) As the tourmaline-bearing partings in the limestone at 

 Changkat Pari constitute a case of selective metamorphism, so it is 

 thought that the tourmaline-corundum rocks, as a whole, mark a 

 process of selective and intense metamorphism in beds associated 

 with schists overlying the Kinta limestone. 



(7) These beds were probably chert and silicified limestone, both 

 being in many cases carbonaceous. 



(8) The large cavities and bodies mentioned in (2) are believed 

 to be the result of replacement or partial replacement of oolitic 

 grains. 



(9) The smaller bodies may be, in part, the result of replacement 

 of the materials forming casts of radiolarian structures ; in part, the 

 further development or replacement of spots, such as those seen in 

 the soft partings found in the limestone at Changkat Pari ; and in 

 part, the result of the replacement of small oolitic grains. 



EXPLANATION OF PLATES XXX & XXXI. 



[The magnification in both plates is about 12 diameters.] 

 Plate XXX. 



Fig. 1. Slice cut from a pebble of silicified oolitic limestone (?). 



2. Round and oval bodies in fine-grained carbonaceous rock containing 



no corundum, and only a little tourmaline as veins. Some of the 

 bodies show a light shell and dark centre, others a concentric light 

 and dark structure. 



3. Fine-grained siliceous rock veined with blue corundum. Some round 



bodies are visible, but the corundum veins run independently of 

 them. 



4. Slice cut from the same rock as fig. 3 : the dark centre of the bodies 



consists of corundum with black dust. The material in the clear rim 

 is too fine for determination. 



5. Round bodies of corundum, partly darkened by black dust and showing 



concentric structure, in a greenish base. 



6. Slice cut from a pebble found in the Ulu Johann, Kinta. Discs and 



rings of corundum with black dust, in a base of white mica. 



