GENERAL GEOLOGY OF TlIK ARKA. d 



Between Tharni and Lurg-huta (one mile south of Tatapani) I could 



trace evidences of a great fault, which is very well 

 Fault. . . 



shown near the junction with the sedimentary 



rocks, where a ridge of fault-rock runs in the line of dislocation. 



The hot spring of Ganduaui is also situated 



Hot spring. 



in this line. 



Crystalline auea. 



Most of the time available had to be devoted to the coal-bearing 



Division of crystalline rocks : it was therefore only possible to examine the 



®^"^^* crystalline rocks of the neighbourhood cursorily ; 



but at least three great groups could be distinguished, namely, the oldest 



gneiss formation, crystalline schists, and granitic rocks. 



The old gneiss formation. 

 This is met with in two areas : first, forming the great Chota Nagpur 



Pats and their slopes to the north, and second, the 

 Gneiss. r» i i ^ ... 



area north of the coal-field in the vicinity or the 



Rer river. The latter is probably connected under ground with the 



gneiss of the t'ats, merely denuded to a lower level (about \,i 00 feet) 



and in parts covered by younger rocks. 



The usual variety of rocks composing the Pats is a coarse, porphyritic 



gneiss, with bands of hornblendic rocks, here and 



Lithological character. , , . . 



there passing into a hornblendic gneiss traversed 



by numerous veins of pink pegmatite and of epidote. 



The profile of the Pats is characteristic enough, rising more or less 

 abruptly into plateaux, and distinguished from the escarpments of the 

 Vindhyans or the upper Gondw^nas by more gradual slopes and irregular 

 outlines, all covered by dense jungles. 



I may here mention the occurrence of rock-laterite with trap 

 Occurrence of laterite ^^ ^ ^^^ VsAiS as akeady described in former 

 with trap. Memoirs. 



The gneissic area north of the coal-field on the right bank of the 



( 131 ) 



