﻿Vol. 66.'] TOURMALINE-CORUNDUM ROCKS OF KINTA. 447 



as to make the section nearly opaque. At one point in the slide 

 there is a spine that may be a sponge-spicule or a detached spine 

 from a radiolarian test (this is not included in the microphotograph) ; 

 but throughout the slide are numerous opaque round bodies with a 

 clear rim. That these are the remains of organic structures, probably 

 radiolaria, is likely, but no recognizable organic structure can be 

 seen in them now. Their significance lies in their resemblance to 

 some of the smaller bodies in the tourmaline-corundum rocks ; and 

 it is a reasonable assumption that these smaller bodies in the Kinta 

 rocks may be the result of replacement of the materials composing 

 such structures in chert or silicified limestone by tourmaline and 

 corundum, the carbon alone of the original structure remaining. 

 This assumption is strengthened by the trace of radiolarian structure 

 in the rock found in the open cut behind Redhills ; on the other 

 hand, it is necessary to emphasize the fact that in the tourmaline- 

 corundum rocks themselves no trace whatever of radiolarian 

 structure has been seen. Another point against the radiolarian 

 origin of any of the smaller bodies is that in the Pahang chert 

 the remains of sponge-spicules are occasionally found, whereas 

 nothing has been seen in the tourmaline-corundum rocks that 

 can, with anything approaching certainty, be referred to such 

 spicules. The concentric structure seen in some of the smaller bodies 

 composed of corundum may point to an origin from small oolitic 

 grains. 



Never having been able to take the opinion of another petrologist 

 on these rocks as they occur in the field, and describing them 

 now for the first time to an audience, many members of which 

 are probably unable to visit the district, I feel that it is a very 

 difficult task to convey an adequate idea of the peculiarities of the 

 tourmaline-corundum rocks of the Kinta Valley, and more especially 

 to put forward any convincing argument in favour of the hypo- 

 thesis that seems most acceptable with regard to their mode of 

 origin. 



V. Conclusions. 



In conclusion I will briefly summarize the main points in the 

 composition of the tourmaline-corundum and associated rocks, and 

 the hypothesis adopted to explain their origin. 1 



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

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

 other minerals. 



(2) They contain cavities measuring about 6 millimetres in 

 greatest width, generally bordered 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, 



1 Much that is of interest concerning the association of corundum with 

 tourmaline, spinel, and rutile will be found in ' A Manual of the Geology of 

 India — Economic Geology : Pt. i. Corundum ' Calcutta, 1898. 



