24' EAMGUIIII COAL PIELD. 



of metallic lodes. "With regard to a large proportion of it^ the latter 

 seems, for the following reasons^ to be the more correct view :— 



First. — It does not seem to have affected the neighbomnng rocks as 

 we should expect it to have done had it been intruded in a molten 

 condition. 



Secondly/. — In some of the lodes, the formation of the granite seems 

 to have been from some cause arrested, and we find that the deposition 

 having commenced on the walls of the joints, proceeded thence to the 

 centre, but that the source of the granite minerals was cut off before 

 the opposing faces succeeded in meeting. 



The regular metamorphic series is represented in this area by- 

 several varieties of gneiss, &c. ; the succession in ascending order being 

 approximately as follows : — 



Porphyrytlc gneiss. 



Granitic „ 



Syenitic „ 



Felspathic „ 



Quartzites. \ Alternating with 



Mica-schists. | one another. 



Actinolite and hornblendic schists. 



Sandstone like gneiss. 



Hornblendic schists. 



] 



The dip of these rocks varies very much, being sometimes as low as 

 20°, but more frequently it is close upon the ver- 



Dip. 



tical ', the prevailing direction is due north in the 



southern portion of the area, but in the vicinity of the Bokaro Coal-field, 



it bends round towards the east. 



The lowest of these rocks, the porphyrytic gneiss^ is the most 



interesting member of the series, whether we re- 



Porphyrytic gneiss. i • , « t , i i • i i • i • , n 



gard it from a lithological or a geological point of 



view. It is composed of mica (two species), quartz 



and orthoclase felspar, the latter occurring ])oth 



in the general matrix and in peculiar twin crystals which in section form 

 ( 133 ) 



