STREAM TIN DEPOSITS OF PERAK. 239 



jected to mere heat, it would have run together in the form of 

 pure metal as it does in the smelting furnace. But under heat 

 pressure and with water, it is forced to combine with oxygen gas, 

 a combination which is not easily effected without those conditions. 

 Tin when kept at a red heat with free access of air; oxidizes readily. 

 There are two forms of oxide of tin, one in which one volume of 

 tin combines with one volume of oxygen, this is called the proto- 

 xide or stannous oxide obtained by chemical precipitation. It is 

 a very unstable compound, and on slight application of red heat » 

 makes it burn like tinder and become stannic oxide. There is the 

 second combination, or peroxide of tin, in which one volume of tin 

 is combined with two of oxygen. This is the common ore of tin. 



If heat alone had been concerned in the production of the tin 

 which is found, it would have occurred in a different way. The 

 peculiar oxide of tin, which is so familiar to you here, is a state of 

 the mineral which can hardly be adequately explained, unless formed 

 slowly. Crystals of Cassiterite may have been formed by the sole 

 action of water just as crystals of silica are so formed. But the 

 proximity of the granite renders the conclusion more probable that 

 the agencies of heat, pressure and superheated steam have been all 

 in operation in the production of this oxide of tin. 



Usually, the form of the fragments of Cassiterite in the drifts 

 is not crystalline. You do find many crystals, but the majority of 

 the grains are angular and amorphous. The edges are very clean 

 and sharp, and not often manifesting any marks of abrasion. They 

 resemble in this respect the fragments of quartz washed out of 

 granite which are associated with them in the drift. From this 

 I conclude that the tin has been amalgamated in the matrix or 

 other rock paste just as quartz, felspar and mica are. 



I am rather diffident in propounding a theory as to how this 

 may have occurred. Supposing, however, tin to have been finely 

 disseminated through the formation which went to form the gra- 

 nite, it may have been sublimed and then condensed on the edges of 

 the strata where the metamorphism was not complete. Thus it is 

 found at the junction of the granite with the stratified rock. The 

 use of the terms subliming and condensation may be a little mis- 

 leading. I only use them as generally expressing the category to 

 which the processes may have belonged. As a matter of course, 

 they must have been different, because the conditions were differ- 

 ent from anything which we can reduce to experiment. 



I am aware how unsatisfactory any theory is which cannot be 

 brought to some test for its verification. In this matter, however, 

 we must rest content with explanations which are little more than 



