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occurs abundantly in large idiomorphic crystals in a zircon 

 granite. Common in gem washings, and usually well crystallized. 

 Colour various : brown, yellowish, green. The colourless varieties 

 are known as Matara diamonds ; the coloured as jargoon and 

 hyacinth, used as gems. 



77^0/7^6', ThSi04. 



Apatite^ Ca4(CaF)(P04)3. — A microscopic constituent of many 

 granulites. Blue apatite is very characteristic of the crystalline 

 limestones. 



Fergusonite, (YErCe)(NbTa)04. 



Anhydrite, CaS04. 



Uraninite {PitcJMende). — Uranate of lead, the chief source of 

 radium. Not certainly known to occur in Ceylon, as all supposed 

 specimens may be thorianite. 



The above forms a complete list of the minerals at present 

 known to occur in Ceylon ; the discovery of others may -be 

 expected ; minerals of the samarskite and asschynite groups are 

 probably present. 



For further information as to the rocks and minerals the 

 following works may be consulted, amongst others : — 



Weinschenck, E. Zur Kenntniss der Graphitlage'rstatten ; Die 

 Graphitlagerstatten der Insel Ceylons. Zeit. fur prakt. Geol.; 

 1900, p. 174. 



Griinling, F. Ueber die Mineralvorkommen von Ceylon. Zeit 

 fur Kryst, vol. XXXIIL, 1900, heft 3.5, pp. 209-239. 



Coomaraswamy, A. K. The Crystalline Limestones of Ceylon. 

 Quart. Journ. Geol. Soc, vol. LVIII., 1902, pp. 399-422. 



Coomaraswamy, A. K. The Point de Galle Group (Ceylon); 

 Wollastonite-scapolite Gneisses. Quart. Journ. Geol. Soc, vol. 

 LVIII., 1902, pp. 680-689. 



III.— ROCKS OF SECONDARY ORIGIN. 



Of these, Laterite (cabook) is perhaps the most important. It 

 commonly occurs overlying quite unaltered granulites, forming 

 a mantle varying from a few feet to many yards in thickness in 

 different places, but is of rather local distribution. When dug it is 

 soft, but as it hardens on exposure it forms a useful building 

 stone. Typical laterite is a decomposition product of the rocks 

 beneath, and is especially characteristic of tropical lands. Laterites 

 are usually found to consist of a fine-grained scaly aggregate of 

 hydrargillite or similar aluminium hydrate, with also ferrous 



