CHAPTER IX. 



LATERITE. 



At least two varieties of this remarkable rock occur in and in .the 

 vicinity of the Rajmehal hills. 



Laterite of the ordinary character is met with forming irregular 

 patches on the metamorphic rocks to the west of the hills, from Suri 

 northward to the Ganges. 



The more special form of it, which rises to a thickness in some places 

 of 200 feet, commences with the western scarp of the trappean rocks, 

 stretching thence eastwards, forming a wide-spread coating over the 

 older rocks, and so sloping down into the eastern plains, where in some 

 places it has by weathering been reduced into a detrital condition. 



Many of the sections in the hills shew a very intimate connection 

 to exist between the laterite and basalt upon which it sometimes appears 

 to be incrusted, and the conclusion that its iron is derived from that 

 source seems a natural one to draw. Again, on the eastern flank of the 

 hills, there are many outlying deposits of laterite with which white and 

 purplish clays are interbedded. This association suggests the idea that 

 the laterite may, in these cases, be merely modified basalt, while the clay 

 beds represent inter-trappean layers. Proof of this view, however, is 

 altogether absent. 



In the hills south of Sahibganj, I observed that the incrustation of 

 the trap commenced at about the level of 600 feet, above which, often 

 for several hundred feet, no trap in its pure state was exposed. This 

 level of the base of the laterite is, however, by no means general ; for, as 

 has already been indicated, it slopes from the top of the high scarps on 

 tbe west to the plains on the east. 



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