656 Geological Society. 



a thin cap of schists, with which are found certain rocks the 

 two chief constituents of which are tourmaline and corundum. 

 They are often carbonaceous ; and, in the many variations found, 

 white mica, brown mica, pleonaste, rutile, and metallic sulphides 

 occur. 



The tourmaline-corundum rocks contain certain structures which 

 are described in detail. These consist of round and oval cavities 

 and bodies, the largest of which are about 6 millimetres in greatest 

 width. Nothing can be proved regarding their origin, but the 

 description of the rocks is summarized and an hypothesis adopted 

 regarding their history, as follows: — 



(1) The tourmaline-corundum rocks of Einta consist of varying 

 amounts of tourmaline, corundum, carbon, white mica, spinel, and 

 other minerals. 



(2) They contain cavities about 6 millimetres in greatest 

 width, generally bordeied by a layer of corundum grains, with 

 tourmaline grains on the inside of this border. Sometimes solid 

 bodies similar in size and shape to the cavities occur. They are 

 composed of tourmaline and corundum : the former mineral, 

 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 tourmaline and corundum. AVhen both 

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

 tourmaline. The corundum bodies frequently show 7 concentric 

 structure. 



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

 rocks, which lead to the conclusion that the structures described in 

 2 & 3 are the result of replacement of the materials of pre-existing 

 bodies at the time of extensive granitic intrusions. 



(5) They also are 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 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 larger 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 easts of radiolarian structures ; in part, 

 the result of the further development or replacement of spots seen in 

 soft partings in the limestone at Changkat Pari ; and, in part, the 

 result of the replacement of small oolitic grains. 



