﻿178 



DR. W. R. JONES ON THE SECONDARY 



[vol. lxxii, 



occurrence is seen on the property of the Gopeng Tin Mining Company, where 

 the tin-bearing stratum consists of a more or less ferruginous deposit of sandy 

 and gravelly material occupying a ridge on the side of a small stream and 

 underlaid by a pebbly stratum like that just described. In the creek-bed 

 below, near the native town of Gopeng, tin-alluvium washed down from the 

 ridges is extensively worked by the Chinese.' 



Deposits such as these, when subjected in the mine to water 

 under great pressure for hydraulicking the beds, leave exposed faces 

 which certainly bear resemblance to a cutting in glacial clays ; for, 

 not only does the water destroy any structure that the beds pre- 

 viously preserved, but the pebbles are broken up, and, when the 

 talus at the foot of the face is washed by powerful jets of water, 

 the broken pebbles are hurled against the working-face. The 

 photograph, for example, illustrating Mr. Scrivenor's article in the 

 ' Geological Magazine ' for July 1914 (p. 310), was taken in 

 my presence, and is of a working-face that had been subjected 

 to water from a monitor under a pressure of 80 lbs. to the square 

 inch. In the photographs in the memoir on the Kinta district 

 (pi. iii, fig. 1) it will be noticed also that the boulders are much 

 more sharply angular than those usually associated with glacial 

 ■deposits. 



At the Tekka Ltd. Mine a boulder of tourmaline-schist, obviously 

 part of the tourmaline-schist occurring in situ a few yards away, 

 was found completely surrounded by the supposed glacial clays ! 

 This proved conclusively that the clays could not be older than 

 the granite which gave rise to the tourmaline and associated 

 minerals. The boulder was cemented with chalcedony, which 

 enabled it to preserve its structure. 



At Gopeng the beds contain numerotis boulders of schists, and. 

 in places, notably near the large kaolin-vein recently sampled by 

 me, 1 these boulders, although friable, still preserve distinct folia- 

 tion-planes, and occasionally contain small veinlets of tourmaline 

 and cassiterite traversing individual boulders. 



(b) The Rocks and Minerals present in the Clays occur 

 in situ in the Schists, Phyllites, etc. The Relation 

 between their Distribution and the Drainage System. 



It is agreed that tourmaline-corundum rocks are found in the 

 •.clays and ' boulder-clays ' only of the west side of the Kinta River, 

 but Mr. Scrivenor does not regard the river in any way as the 

 cause of the fact that it divides the clays containing tourmaline- 

 corundum rocks from those which do not, but looks upon it 



' as a remarkable accident, but one that enables us to conveniently distinguish 

 the clays with tourmaline-corundiun rocks as the western boulder-clays, as 

 opposed to the eastern boulder-clays of Gopeng, Pulai, etc' 2 



1 W. R. Jones, ' Clays of Economic Importance in the P.M. States ' Kuala 

 Lumpur, Government Printing Office. 1915, p. 3. 



2 J. B. Scrivenor, ' The Geology & Mining Industry of the Kinta District ' 

 1913, p. 28. 



