STREAM TIN DEPOSITS OE PERAK. 233 



when it is melted and cooled, or slowly cooled if you will, becomes 

 granite. 



But against this theory we know many instances of the melt- 

 ing of the earth's surface by heat, and when cooled it becomes 

 something very different from granite. Volcanoes emit from 

 their craters the melted materials of the crust of the earth, but Java 

 is not at all like granite, and even where it has cooled slowly it 

 is still very different. 



Heat alone, then, will not suffice as a theory. A simple reflex- 

 ion will make us realize this better. Granite is in structure not 

 unlike a piece of loaf sugar. But in the case of the sugar the 

 structure is not due to mere heat, as I need not tell you. If you 

 take the sugar and melt it over a fire, what a different material it 

 becomes, and so it is with granite. If it be melted, which it re- 

 quires an enormous heat to effect, the result, when cooled, is a mere 

 slag. 



Besides, if granite be closely examined, a curious feature in the 

 crystals will be noticed. The mica and the felspar have both left 

 the forms of their crystals imbedded on the quartz. But the 

 quartz cools at a much higher temperature than the mica or fel- 

 spar. ]f heat alone had been in operation, the quartz should have 

 cooled first and left its crystals to modify the other two minerals. 



But for all that, geological research proved beyond a doubt 

 that, melted or softened in some sort of way, granite had formerly 

 been. At its junction with stratified rocks it was frequently found 

 to throw out veins into fissures, and to be injected, so to speak, as a 

 molten material could only be expected to do. Granite dykes or 

 elvans are not uncommon, and these sometimes in granite itself 

 showing that the encasing material of which the walls of the dyke 

 are formed had cooled or solidified to some extent before the latter 

 was injected. "When granite is found in contact with stratified 

 rocks, the latter are usually much changed, and as if the crystal- 

 line rock had affected them b}^ its heat. When this is not the 

 case, it can generally be proved that there has been considerable 

 displacement and upheaval since the granite was melted. The tilted 

 stratified rocks which lie against it came to their present position 

 in a later period in the geological history of both formations. 

 Sometimes gradual transition from stratified rock to granite may 

 be observed, so that it is difficult to say where one begins and 

 the other ends, and even where the unaltered slates which lie 

 near granite are submitted to microscopic examination. Occa- 

 sionally in granite itself marks of former stratification can be 

 made out. Blocks of evidently stratified rock are found imbedded 



