﻿446 MR. J. B. SCRIVENOR ON THE [Aug. I 9 1 °i 



arrangement is as follows : — On the outside is the clear ring, 

 then a ring in which the white opaque substance is abundant, and 

 a nucleus in which a micaceous mineral predominates, appearing 

 clearer than the inner ring, but not so clear as the outer ring. 

 These rocks instantly suggest spotted schist, but it is impossible to 

 determine how the spots originated, whether they mark the remains 

 of some pre-existing structure, or the incipient growth of a 

 secondary mineral, as some spots mark the first appearance of 

 andalusite. Another noteworthy point in these partings in the 

 crystalline limestone is that nearly all the sections cut from them 

 contain abundant, and very minute prisms of tourmaline, while no 

 tourmaline has been found in the limestone. The tourmaline prisms 

 also occur in the nuclei of the spots. 



The structures in the tourmaline-corundum rocks fall into two 

 classes — the larger solid bodies and cavities, measuring about 6 milli- 

 metres in greatest width, and the smaller solid bodies. We have 

 also to consider the dark nodular masses seen in (vii)e, p. 441. 



To take the larger solid bodies and cavities first : the first point 

 that strikes one is that they are a development of the structures 

 described under (v), p. 440, and an examination of the slides sub- 

 mitted with this paper will show that the rocks containing these 

 structures are probably silicified oolitic limestones, with a secondary 

 development of mica. It is impossible to assert that the large solid 

 bodies of tourmaline, corundum, and other minerals are replacements 

 of oolitic grains, beecause as yet no calcareous oolitic grains have 

 been observed in the Kinta limestone at all. But oolitic limestone, 

 supposedly of the same age as the Kinta limestone, occurs in Pahang, 

 and there is no a priori reason why such limestone should not have 

 been part of the Kinta series. The marked concentric structure so 

 often observable in the tourmaline-corundum bodies is strongly in 

 favour of the hypothesis of the original structures having been 

 oolitic grains, and more than that, I think, cannot be said. A 

 better suggestion would be welcome. 



I have only a tentative suggestion to offer for the origin of the 

 dark nodules in (vii) e. A specimen sent with the exhibit to illustrate 

 this paper shows dark structures that recall organic remains. In 

 (vii) e it was found that the dark nodules contain more corundum 

 than the rest of the rock, and it is conceivable that organic remains 

 in a pre-existing limestone absorbed more alumina during the 

 process of metasomatism than the rest of the rock. Against this 

 we have to remember that the nodules in (vii) e enclose small round 

 bodies resembling those in the lighter portion of the rock. 



I have indicated above that the beds from which the tourmaline- 

 corundum rocks were derived were laid down under conditions 

 similar to those under which the Pahang Chert Series was 

 deposited. Distinct remains of radiolaria are not common in the 

 Pahang cherts ; but of commoner occurrence are circular clear spots 

 and bodies such as those illustrated in PL XXXI, fig. 6. This 

 microphotograph is taken from a section of a dark carbonaceous 

 chert exposed at the Bentong Reservoir. Carbon is so abundant 



