GEOLOGY OF INDIA. 7 



" The most prevailing species is granite or gneiss, the more limited 

 are quartz rock, hornblende rock, drnd dolomite rock, and a few others which 

 may be considered under the head of embedded minerals. 



" The varieties of granite and gneiss are innumerable, passing often 

 from one into another, and assuming appearances for which, in small 

 masses, it would be difficult to find out appropriate names, depending on 

 composition and the proportions of the elements — or addition of new 

 ingredients ; regular granite is not common, graphic granite still rarer, it 

 occurs at Trincomalee — neither is sienite common, it occurs in the Can- 

 dyan provinces. Well formed gneiss is more abundant than granite, it 

 frequently consists of white felspar and quartz in a finely crystalyzed 

 state, with layers of black mica, containing numerous crystals of light 

 coloured garnets. A similar rock is found on the opposite Continent, in 

 the mountains at Cotallum, and affords one amongst other evidences of a 

 conformity, if not indentity, in geological character. Both the granite and 

 gneiss of Ceylon, are much modified by an excess or deficiency of one or 

 other of the ingredients. When quartz abounds in a fine granular state, 

 the rock looks like sand-stone. When felspar or adularia abound, it ac- 

 quires a new external character. This variety is common, and in some 

 places it contains so much of these minerals that it may be called adularia, 

 OY felspar rock. When mica prevails in gneiss, (which is rare) it acquires 

 not only the appearance, but very much the structure of mica slate. 



The more limited varieties of primitive rocks, as quartz, hornblende, 

 and dolomite rock, seldom occur in the form of mountain masses. The 

 rocks of recent formation are lime-stone and safid-stone. The former is con- 

 fined to the northern shore of the Island, where it appears to be still form- 

 ing in the coral shallows of the adjoining sea. The other, (sand-stone) a 

 rock of pretty general occurrence along the shore of the Island, which it 



may 



