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25- Though the prevailing rocks of Bengal and Bihar are 

 Old or New alluvium, there are some important exceptions. 

 First of all we will describe the laterite region of Bengal, 

 which is also post-tertiary. This laterite region can be traced 

 up from Cape Comorin along the East coast, througn Orissa, 

 Midnapur, Bankura, Burdwan, Birbhum, to the flanks of the 

 Rajmehal hills as far as Patna. This fringe of laterite un- 

 derlies the old alluvium and is older than alluvium. It is 

 often seen capping older rocks. This is the High Level 

 Laterite already described in Chapter I. The Low Level 

 Laterite is truly alluvial and it occurs in patches throughout 

 the Old alluvium of the Ganges valley. 



26. The Pleistocene or glacial boulders and moraines are 

 not represented in Bengal, except in the lower hills of Sikkim, 

 Bhotan and Nepaul, down to a height of about 3,oooft. above 

 the level of the sea. 



27. Next we come across in Bengal a band of the Cadda- 

 lore group of rocks, sandstones, grits and clays, underlying 

 laterite, from east of Raniganj extending northwards as far 

 as Suri. These Caddalore sandstones &c., are tertiary. 

 At a lower elevation in the Sub-Himalayan range, on the 

 north of Bengal, there is a band of soft massive sandstones, 

 also clays and conglomerates, resting on the older tertiary 

 bed of Nummulitic limestone. This belongs to the same age 

 as the Caddalore band from Raniganj to Suri. 



28. The Eocene sandstones, Nummulitic limestones, and 

 the cretaceous chalk, the pre-tertiary slates and sandstones 

 are found in the Chittagong, Tippera, Garo and Manipur hills. 

 Tertiary rocks prevail in these hills which were probably 

 elevated at the post-tertiary age about the same time as 

 the Gangetic delta from Rajmehal to the Garo hills was 

 depressed. 



29. The Jurassic system is next represented in Bengnl in 

 the Rajmehal hills and the Upper Panchet series of rocks. The 

 typical Rajmehal rock is a basalt or trap consisting of dark 



