144 R. A F. PENROSE 



there has been an elevation of the region followed by subsequent 

 erosion, with the result that the older tin alluvium occupies the 

 higher places, while the younger alluvium, derived probably in 

 part from the older deposits, occupies lower levels, in much the 

 same way as the Tertiary gold placers of California often occupy 

 the higher spots and the more recent placers are found in the 

 present stream beds. This may be true in some of the tin 

 deposits, but it is necessary to distinguish between such occur- 

 rences and the cases where the tin deposits on the higher places 

 are simply residual deposits formed i?isituhy the superficial decay 

 of tin-bearing rocks, without removal of the tin from the region 

 of its source. 



Nature of the tin ore in the Kitita district. — The tin occurs in the 

 form of cassiterite or oxide of tin (SnOg), often well crystal- 

 lized in tetragonal prisms with fine terminations, though the 

 fragments in the alluvium have been more or less rounded by 

 attrition. The ore varies in color from black or brown to gray, 

 grayish-green, white, or transparent, but the commonest kind is 

 of a dark brown or almost black color with a resinous luster. 

 In the mountains, near its source, the ore is angular and in com- 

 paratively large fragments, sometimes from an inch to a foot or 

 more in diameter, but this is rare, and farther down hill it 

 becomes more and more rounded and fine-grained, the common 

 alluvial tin fragments ranging from the size of peas to that of 

 sand grains or smaller. In fact, efforts are now being made to 

 work tin ore that exists as a fine powder in the mud banks that 

 line certain parts of the west coast of the peninsula. 



The amount of tin in the ore as commercially mined ranges 

 from 69 to 73 per cent., an average of about 70 per cent, being 

 considered very fair. The theoretical amount of tin in cassiterite 

 is 78.6 per cent. The richness of the tin ground varies much in 

 different places. The average value of the alluvium worked in 

 the Kinta district is probably about i per cent, of cassiterite, and 

 ground of this grade pays well to work, if favorably situated. 

 If the alluvium contains 2 per cent, of cassiterite, it is considered 

 exceptionally good ground, and with 3 or 4 per cent, it is con- 

 sidered remarkably rich. Sometimes thin strata in the alluvium 



