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hydrate varying in amount according to the nature of the parent 

 rock. When the latter contained free quartz, it is found in the 

 laterite in angular grains. 



Various Clays, including kaolin (China clay), are also found, and 

 are also decomposition products of the granulitic rocks. They 

 differ chiefly from laterite in consisting rather of aluminium 

 silicates than of aluminium hydrate. 



Cherts and common-opal rock are sparingly found, often in 

 association with crj^stallme limestones, and can sometimes be 

 shown to have been formed by pseudo-morphous replacement of 

 the latter ; specimens occur containing the phlogopite, graphite, 

 and spinel of the original crystalline limestone, as well as others 

 in which remains of the partially disintegrated carbonates can 

 still be seen. 



Travertine (tufa) is a secondary deposit of carbonate of lime 

 (apparently sometimes containing magnesium carbonate as well) 

 removed in solution from the beds of crystalline limestone ; but 

 these deposits are but rarely found in large quantity. 



IV.— FOSSILS AND RECENT SEDIMENTARY ROCKS. 



Even less is known of these than of the crystalline rocks. A 

 belt of raised beach deposits is almost everywhere to be traced 

 around the coast, extending to no great height above sea level. 

 The material composing the deposit varies from a sandstone 

 cemented by calcareous material to a rubbly rock composed 

 entirely of the debris of corals and other calcareous organisms. 



A series of recent marine fossils from Palanti-aar is exhibited, 

 and includes shells in a calcareous breccia, and well-preserved 

 remains of crabs in nodules of mud. There are also fossil chank 

 shells from the Kadurawala coast ; the latter are regularly 

 quarried in the recent deposits of the Jaffna District. 



An interesting specimen of a bone and shell breccia from the 

 floor of a Vedda cave is exhibited ; but little is known, however, 

 as to the occurrence of really ancient cave deposits ; masses of 

 stalactite are rarely found in caves in the crystalline limestones. 



In addition to the recent marine sedimentary deposits, there are 

 river gravels and alluviums. Thick beds of the former are of 

 somewhat rare occurrence, but rivers, large or small, are not 

 infrequently bordered by strips of alluvial deposits, and when 

 they leave behind the mountain country, and with it their often 

 torrential character, debouch upon extensive alluvial plains where 

 fine silty muds are still deposited in times of flood. The fine 

 muds thus laid down are of great value in the manufacture of 

 bricks and the coarser kinds of earthenware. 



