23G STHEAM TIN" DEPOSITS OF PERAK. 



also chemically combined, and also water in its simple form, mixea 

 or soaked in we may say, and from which no compound rock is ever 

 free. 



Now. consider the effect of heat caused by pressure on these 

 materials aided by the presence of water. The latter material, you 

 know, at the surface of the earth cannot be heated much above 212 D 

 degrees of Fahrenheit. Then it evaporates in the form of steam. 

 But under great pressure, -of course it cannot evaporate. It may 

 be then heated to any extent that the pressure will bear. Water, 

 even cold water, is a solvent of rocks to a far greater extent than 

 you would imagine, not only by wearing them away, but by really 

 dissolving the stone. But at very high temperatures water acts on 

 rocks such as quartz more powerfully than the strongest acid does 

 upon iron at the earth's surface. Let us take dull red heat, for 

 instance, and 1 will tell you presently why I choose that degree of 

 heat. At this temperature, quartz would be readily dissolved by 

 superheated water, while I need not tell you that it requires a 

 considerably higher temperature to melt it in the air. 



These conclusions are not the result of mere theor}^. Experi- 

 ments have proved them. By means of carefully secured vessels, 

 water has been raised to a red heat and even higher, and its action 

 upon quartz, glass and many other substances observed. If I do not 

 mistake, after an experiment which lasted some IS months, some of 

 the minerals of granite and something very like granite have been 

 reproduced by Mons. Datibr&e. 



This pressure, or the weight of the superincumbent rock, is quite 

 sufficient to account for the change of stratified rock into granite. 

 Pressure has generated heat, heat has brought into action the 

 highly corrosive and solvent action of water, chemical action has 

 been set up, those elements that have the greatest affinity for each 

 other have united, acids have neutralised alkalies, gases have been 

 liberated and made new combinations, and finally minerals have 

 segregated, and the result is the rocks in the form in which we see 

 them now. 



Be it remembered that though we class the rocks of this Bange 

 under one category, which we distinguish as granite, the rock is 

 very varied in its constitution. It is fine grained, and coarse, 

 blue and red, dark coloured and light. Some of it is almost all 

 quartz and some foliated like a schist. Mica predominates in 

 one place, and there are thick veins of felspar in another. All 

 this is just what we should expect. The stratified rock was not 

 of uniform character, but even if it were, the pressure would pre- 

 vent the reduction of the whole into a rock of simple mineralogi- 



