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THE ROCKS AND MINERALS OF CEYLON. 



1>Y A. K. COOMARASVVAMY, B.SU.. 

 Director^ Minerali)(ji<-al Sitrrei/ of Cei/loit. 



I.— ROCKS. 



The rocks of Ceylon are known as diniillllites, or, using the 

 term in its widest sense, as Gneisses ; they belong to the same 

 series as that which Mr. Holland has named in Southern India 

 the Cliariiockite Series. The rocks are crystalline and show con- 

 spicuous mineral banding (foliation), and are very varied in 

 mineral composition. Rocks of igneous origin form by far the 

 greater part of the Charnockite Series in Ceylon, although it is 

 possible that amongst these rocks there are some of sedimentary 

 origin now highly metamorphosed and incorporated with the 

 others. Tlie bedded appsarance so suggestive of sedimentary 

 rocks is in this respect deceptive, and is due to the banded 

 structure produced by flowing movements in the hetero- 

 geneous magma during its consolidation. No fossils occur in any 

 of the crystalline rocks. 



The most characteristic types of rock exhibited include 

 "Taimlar qiuirtz rock, consisting essentially of quartz, but often 

 with minute quantities of felspar and garnet; leptyilites, composed 

 of quartz and felspar, and very often containing an abundance of 

 garnet ; typical eUariiockite, essentially composed of felspar quartz 

 and hypersthene ; pyroxene granulites, characterized by the 

 presence of pyroxene (hypersthene or augite or both) with 

 felspar (usually triclinic) and with or without orthoclase, quartz, 

 or garnet ; amongst these are rocks with the mineral composition 

 of iiorites, diorites. and }i;abbroS ; there are also more basic types 

 consisting almost entirely of pyroxene, ampbibole, and garnet ; 

 these dark heavy rocks frequently occur as lenticular bands and 

 inclusions in the more acid types. Coarse-grained pegmatites of 

 an intrusive character arc found in dykes and veins crossing or 

 parallel to the foliation of the other rocks ; in them the minerals 

 quartz, orthoclase, mica, and hornblende are most characteristic ; 

 the quartz and felspar are often intergrown as in nTa])hic»'i'ailite. 

 The crystalliue limestones are found in wide or narrow bands 

 interbedded with the other rocks, often separated from them 

 by a zone of heavy dark green rocks composed essentially 

 of pyroxene and mica, often with spinel. The limrstoiies 



