STREAM TIN DEPOSITS OF PERAK. 227 



have been derived from similar rocks. I call them Ordovecian, 

 a term proposed for the Upper Cainbian series, but I merely sug- 

 gest this age as probable. They much resemble the Ordovecian 

 of Australia, though the precise age cannot as yet be proved. 



It is probably under these clays, at their junction with the 

 granite, the great deposits of tin ore took place. All mining 

 geologists are aware, that when any metal is contained in a rock, it 

 will be most abundant at the junction of that rock with another 

 formation. I do not undertake to explain why it is so, but I merely 

 state the fact. The junction of two formations is the locality 

 where metallic deposits must be looked for. The whole of the 

 granite in the peninsula contains tin, but it is at the junction of 

 this granite with the paleozoic clays that the richest deposits of 

 tin ore have taken place. 



Thus the red clays become a good indication where tin sand 

 may be looked for. But observe: it is not at this junction that 

 mining takes place. It is when the clay has been washed away 

 and the tin washed out of the junction ; when it has been sifted 

 and sorted by streams of water that the stream tin has been depo- 

 sited where miners get it now. Not at the base of the clays, but 

 in the drift which has been derived from the clays and the gra- 

 nite together. 



It may, be asked, therefore, whether it would be worth while to 

 mine through the clays where they have not been denuded and 

 look for tin at their junction with the granite. I think it would 

 be worth trying. I do not think the tin sand would be likely to 

 prove so rich as in drift where it has been subjected to ages of 

 washing and puddling from the streams. Tin sand is found upon 

 the clays throughout Thaipeng and the neighbouring hills. I can- 

 not even give a guess at how thick these clays are, except that I 

 do not think they can be very thick. I repeat that it would be worth 

 while trying whether there is what miners term a second bottom. 



Observe also that I do not think that the tin deposits are mere- 

 ly confined to the junction of the granite with the paleozoic clays. 

 The ore may be found at the junction of the granite with any rock. 

 On the other side of the range, we seldom see these clays, but in 

 place of them we have limestone and marble abutting on the 

 granite. Here also tin is found and in great richness. 



So, those who go prospecting may take the presence of such 

 formations as a favourable indication, especially where there are 

 high ranges near so as to secure the destruction and thorough wash- 

 ing of the overlying rock. 



If any one asks why we do not find tin in such places as Singa- 



