[ 3* ] 



about 120 miles wide, separate the transition rocks of Bihar 

 from those which occupy parts of Manbhum and Singbhum 

 in South- West Bengal and stretch far to the west, the whole 

 transition area here being 150 miles long from east to west 

 and 80 miles wide. The prevailing character of the rocks 

 here may be best explained by an enumeration of the prin- 

 cipal kinds that occur on the surface. These are quartzite, 

 quartzitic sandstone, slate, shales, hornblendic, micaceous, 

 talcose and chloritic schists passing into bedded trap, shales 

 with ripple marks so little metamorphosed that they might be 

 mistaken for Talchers, or the Lowest Gondwana shales, but for 

 veins of quartz penetrating through them. The Chutia Nag- 

 pur gneiss is interbedded with micaceous, hornblendic and 

 sileceous schists, and occasionally bands of porphyritic 

 granite and highly metamorphic schists. In Singh'bhum the 

 oldest or Bundelkhund gneiss is seen in junction with transi- 

 tion rocks, interpenetrated by trap dykes. Sandstones and 

 mudstones, resting immediately on the rough and weathered 

 surface of the granitic gneiss traversed by trapdykes, is the 

 prevailing character of the Singhbhum soil. " Dome Gneiss" 

 prevails in the northern fringe of the Hazaribagh plateau 

 and the Mandar hill of Bhagalpur. Trapdykes though com- 

 mon in the Bundelkhund gneiss are rare in the Bengal gneiss. 

 We do not see the same extensive basaltic intrusions in 

 southern Monghyr, Hazaribagh and Chutia Nagpur as we do 

 in Birbhum where they belong not to the archaean but to the 

 Rajmehal age. 



34, We have thus seen that although the prevailing charac- 

 ter of the soil of Bengal and Bihar is alluvial, either old or 

 new, we have important exceptions all over the outlying dis- 

 tricts, where rocks of older epochs prevail 



35. The age of rocks can be only vaguely guessed by 

 their texture. The study of fossils alone gives us exact 

 clue as to which period a particular sandstone, or 

 a particular limestone, or a particular shale, belongs. 



