STREAM TIN DEPOSITS OB' PERAK. 225 



attentively by and by. The rest of the plains are river drifts. 



When persons see only narrow streams crossing wide plains, 

 they with difficulty understand how such rivulets could have formed 

 such large areas of gravel, sand and earth. But the cause is quite 

 adequate for the effects, if we remember the constant drainage from 

 the sides of the mouutains. It is unceasingly bringing down new 

 material, which, as it accumulates, throws the stream backwards and 

 forwards. JN'o matter how distant certain portions of the plain 

 may be, as soon as they become the lowest level, the water goes 

 over to it and heaps it up. 



It was the custom, long ago, to explain deposits of alluvium 

 and gravel by theories of great inundations. But great inundations 

 and convulsions of nature have a tendency to destroy and remove. 

 The building up is done by the little stream which, like the busy 

 bee, neatly spreads the materials. The}' may be called nature's 

 chisels which carve and chip the stone, and nature's trowels which 

 smooth and level everything. 



Bear in mind again that the whole of the plains are not form- 

 ed of alluvium. There were inequalities on the surface which are 

 covered over by drift, but of unequal thickness. These, no doubt, 

 were barriers to the waters until the drift rose up to them. 



But not only does drainage level the materials. It sorts them 

 as it carries them along. Lighter portions of granite sand, espe- 

 cially mica, are carried a long distance. Some metals also with 

 light scaly ores, such as specular iron or titaniferous iron, are 

 borne a long way. Heavy metals such as tin, gold and platinum, 

 soon sink and remain behind. 



In another lecture, I shall tell you more about granite, or the 

 rough piece of stone with which we began this evening. But I 

 want to say now that granite frequently contains metalliferous 

 veins and crystals of oxide of tin scattered through it. This latter 

 is a heavy mineral, and is never carried far from the hills. It is 

 enclosed in granite, or at least mixed up with other rock, yet it is 

 gradually sorted out and gathered together. The constant opera- 

 tions of water washes it and buries it in alluvial drift where it be- 

 comes stream tin. Vein tin, from its name, means tin ore occur- 

 ring in lodes or veins, whence it has to be quarried from the 

 solid rock. Vein tin. though in narrow Jodes, goes down to great 

 depths : stream tin is only a shallow 7 deposit of fine ore spread 

 over a wide surface. It is better ore and more accessible, but less 

 permanent than vein tin. 



But has all the alluvial drift of the Larut plains been derived 

 from granite ? I think not. I referred just now to the red clays, 



