﻿438 ME. J. B. SCRIVENOR ON THE [Aug. I9IO, 



Nowhere have I traced any tourmaline-corundum rock inter- 

 bedded with the Kinta limestone ; but, on the east side of the 

 valley, at Pulai and elsewhere, pebbles and boulders of pure 

 corundum are found in the alluvium. This corundum, however, 

 shows none of the extraordinary structures observed in the 

 tourmaline-corundum rocks on the west, and must be considered as 

 distinct. 



III. Description of the Tourmaline-Corundum Rocks and the 

 Associated Schists. 



When I first visited Batu Gajah in 1903, my attention was 

 attracted by a peculiar vesicular rock that was used largely for 

 mending roads and paths and for making concrete foundations. 

 I crushed some of the rock, and found tourmaline to be one con- 

 stituent and probably corundum another. At that time I had 

 no one to prepare sections for me, so sent a specimen of the rock 

 home with others to be cut in England. On their return I found 

 my diagnosis confirmed : if only by a pathetic note on the label 

 4 Hardness 9/ and an extra charge for diamond dust. The mineral 

 was separated, and proved to be corundum in shapeless grains. 



Since 1903 every opportunity has been taken of collecting 

 information about these rocks, but until 1907 their place in the 

 structure of the country remained a mystery. In January 1907 

 my headquarters were moved to Batu Gajah ; and I have been 

 able to obtain sufficient data, while going over the western part of 

 the Kinta Valley, to form as definite an opinion as is likely to be 

 possible under the circumstances regarding the origin of these rocks. 



The schists which cap the limestone on the west side of the 

 Kinta Valley are never well preserved, while sometimes the cap 

 is so thin that surface-water has attacked the limestone under- 

 neath, and reduced the schists to a soft mass in which little or 

 no trace of bedding remains. In some sections, however, the 

 bedding is seen distinctly, and it is evident that the schists, like 

 the limestone, have been subjected to great lateral compression. 



The schists are generally argillaceous, varying in colour owing 

 to the strong weathering, but in some cases they are black and 

 carbonaceous. Frequently, too, the clayey mass lying upon the 

 limestone is very deeply coloured with carbon, derived no doubt 

 from carbonaceous schists. 



Fine-grained sandstone occurs, sometimes associated with the 

 schists ; and at Siak, near Siputeh, there is a long ridge over the 

 limestone which was probably composed largely of fine sandstone 

 before weathering destroyed the continuity of the beds forming the 

 cap. Boulders of sandy schists are common, too, in the detritus 

 from the Gopeng beds, on the east side of the valley ; it is 

 important also to note that on the sandstone ridge at Siak the 

 tourmaline-corundum rocks are only found in small quantity and 

 where they may have been deposited by river-action, while none 

 have been observed as yet at Gopeng. In both localities, how- 

 ever, the sandy rocks contain tourmaline. 



