CHAPTER III. 



General Geology. 



The geological structure of the Rajmehal hills is of a complex 

 character as compared with that of the surrounding country. There 

 are indeed features about these hills which serve to isolate them from 

 every other known area in India. At the same time within their limits 

 the mutual relations of the several rock groups have afforded a key 

 which has proved most useful in the interpretation of the geological 

 structure of several far distant localities. It is to the conditions under 

 which, excepting the Jecent deposits, the youngest rocks of the area were 

 formed that the specially singular characters of the geological features 

 are principally due. 



Rocks of the same age as these, whose fossil contents declare them 

 to belong to the Jurassic period, occur in other parts of India; but no- 

 where except in the Rajmehal hills have we evidence of contemporaneous 

 volcanic activity which, for its extent and importance, can only be com- 

 pared with that of the more recent geological period to which the trap 

 of the Deccan has been referred.* 



In the Rajmehal hills alone, too, do we find sections which serve, 

 by reference to the known horizon of the intertrappean beds, to aid 



* In speaking of the Jurassic rocks of Kach, Mr. Wynne has written as follows : — 

 " Igneous rocks in many cases penetrate these lower jurassics, and in some have a strongly 

 " conteruporaneousjispect, but as the unmistakably intrusive varieties occur with or near 

 " them, the appearance of inter-stratification may be frequently due to intrusion between 

 "the aqueous beds." Mem. Geol. Survey, Vol. IX, p, 50. 



Dr. Feistmantel, in his recently published paper, which has already been alluded to, 

 assigns to the Rajmehal beds a lower position than that which he believes the above to 

 occupy. The Rajmehals correspond, according to hitn, to the Lower Jurassic (or Lias) of 

 Europe, while the Kach beds are more nearly allied to the Middle Jurassic (or lower Oolite) 

 of Europe. 



( HO ) 



