592 MK. A. K. COOMARA-SWAMY ON [Aug. I9OO, 



Laterite (cabook), red or mottled red-and-yellow, occurs 

 abundantly, often of considerable thickness, resting upon, and re- 

 sulting from the decomposition of, the crystalline rocks. The less 

 easily decomposable minerals, such as tourmaline and graphite, are 

 sometimes found in it. 



The rivers, as they approach the sea, flow through alluvial flats of 

 their own deposition. Farther inland coarse gravels are found, 

 or alternations of muddy and sandy or gravelly deposits. Thus the 

 promontory, formed by the loop of the river flowing round the 

 Peradeniya Gardens, consists of coarse crystalline gravel, which is 

 found perhaps 50 feet above the present level of the Mahaweli 

 Gorge. The Newera Eliya Plain consists of alternations of muddy 

 and sandy or gravelly deposits. 



With the exception of moonstone, all the gems for which Ceylon 

 has long been so famous are found in drift -deposits, especially 

 near Ratnapura and Rakwana in the Sabaragarauwa district. Here 

 the gravels are very extensively dug, and gems of great value are 

 discovered from time to time, while stones of less value are very 

 abundant. The gem-stones include ruby, sapphire, white and yellow 

 corundum and ' star-sapphires,' chrysoberyl, cat's-eye, alexandrite, 

 iolite, zircons of varied colour, tourmalines, blue and red spinels, 

 garnet (precious and cinnamon-stone), and topaz. 



Of the rough gems occurring in the gravels at Ratnapura and 

 Rakwana, corundum is abundant and very often in good crystals 

 which are quite large, reaching 4| cm. in diameter and 9 cm. in 

 length. Hexagonal prisms and pyramids are the usual forms. 

 Twinned crystals occur, but are rare. The smaller, or less- worn 

 crystals have sometimes very brilliant unscratched faces and sharp 

 edges. The following combinations were measured by Mr. Graham : — 



(1120) (lOll) (2243) (4483); (0001) (OlTl) (1121); (0001) (2243) 



(1120); (0001) (1011) (2241); (0001) (1011) (4483). 



Zircon is abundant, and usually of a characteristic brown colour, 

 prisms and pyramids being the commonest form. Twins occur. 

 A twin on (101) included the forms (110), (111), (101), (311). Other 

 crystals showed various combinations of the forms (100), (110), 

 (101), (111), (311), (331), (221); all these were measured by 

 Mr. Graham. 



Spinel occurs in rolled octahedra or irregular pieces. 



Gold has been occasionally found in very small quantities in the 

 sands of Ceylon rivers. 



Apparently diamonds have never been found in Ceylon. 



III. The Crystalline Rocks. 



(1) Pyroxene- Grarmlites. 



This rock-type is widely distributed in Ceylon, occurring at 

 Newera Eliya, Kandy, Ragedara, Dondra Head, Matara, Galle, and 

 Colombo. The rock as seen in Ceylon is usually dark, and has a 



