364 me. j. B. sceivenoe on the [June 19 13,. 



the limestone-' cups ' is simple. The limestone is traversed by 

 abundant fault-, joint-, and bedding-planes, -which give facilities 

 for attack by water percolating down slowly from above or by 

 springs rising from below. Part of one divisional plane may 

 afford an easier means of attack than another, with the result that 

 there the limestone is dissolved away more quickly. This soon 

 shows itself in the formation of a ' cup ' or trough on the surface 

 of the limestone, into which the glacial clays must sink, forming a 

 lining to the cavity. The centre of the cavity becomes filled with 

 whatever lies above the glacial clays. The distances from the top- 

 of the pinnacles of the limestone-surface to the bottom of the ' cups ' 

 has not been measured systematically, but the average is probably 

 about 35 feet. The deepest and most interesting of all the ' cups ' 

 known to-day is that in which the famous tin -deposits of the- 

 Tronoh Tin-Mining Company lie. Fig. 2 (p. 363) gives some idea 

 of this 'cup/ and it will be noted that one side of it is bounded 

 by a reversed fault, whereby the limestone and glacial clays have 

 been pushed up against the younger Gondwana rocks. 



The infilling of the ' cups ' is generally lignite, mixed Avith a certain 

 amount of sand, which in some cases forms distinct beds. It is 

 only necessary to consider the course of events, if a stream were fo- 

 llow over the site of one of these ' cups ' when it first began to be 

 formed, to understand the significance of the deposit of lignite. The- 

 solution of the limestone uuder the clay would result in a subsidence 

 of the surface over which the stream was flowing. This would lead 

 to the formation of very marshy ground, where the dead vegetation 

 of the tropical forest would fall and accumulate, mixed with 

 alluvial sand brought doAvn into the swamp from higher ground. 

 So long as the limestone continued to dissolve, the subsidence and 

 accumulation of dead vegetation and alluvial sand must have 

 continued also — sinking ever farther down into the ' cup,' and 

 affording an example of the growth of coal-deposits in situ. 



XT. ToEEENTIAL DEPOSITS. 



When the idea that the clays of the Kinta Valley are glacial 

 deposits first presented itself, particular care was taken to avoid 

 the mistake of ascribing to glacial action boulder-deposits that 

 might have been formed under torrential conditions. The fact 

 that there are in the Peninsula recent torrential deposits, although 

 of a peculiar type, was of great assistance. A brief account of 

 them will be of interest. 



A feature of the granitic outcrops is, that to a depth of 20 

 or even 30 feet, they are weathered to a soft sandy clay that can 

 be cut by hand, but in which veins and faults may still be clearly 

 distinguished. In this granitic clay are numerous cores of hard 

 granite that have resisted weathering. They are of rounded out- 

 line, and when divested of their clayey envelope are generally mis- 

 taken for waterworn boulders. In order to distinguish them from 

 waterworn boulders, I have always referred to them as 'core- 



