328 On the Structure of the Delta of the Ganges. 



existing Sunderbun forests and swamps. Dum-Dum is sur- 

 rounded by shallow salt water lakes, and it is stated,* that 

 many of the names of the adjoining villages indicate that 

 the whole neighbourhood at one period consisted of a series 

 of islands ; but we have no authentic record by which to esti- 

 mate the growth of the Delta in these places, and hence 

 it would have been doubly interesting to have been enabled 

 to assign an epoch to the above remains. It would be use- 

 less to attempt doing so with the imperfect information 

 recorded, but their great size led the officer by whom they 

 were found, to conclude, that they did not belong to any of the 

 animals now inhabiting the Sunderbuns. Succeeding these 

 peat-charged beds, a stratum of calcareous clay, ten feet in 

 thickness, is found, and intermixed with it are portions of 

 that concretionary limestone commonly known in India 

 as kankar. Occasionally this occurs in small grains with 

 the appearance of land shells, sometimes it is found in thin 

 beds of great hardness, and sometimes in its common no- 

 dular shape. Kankar occurs over nearly the whole of India, 

 and abounds in the alluvial formations of Hindustan. In 

 the vicinity of Calcutta, in the bed of the Salt Lake, it is 

 largely met with in the nodular form, and in some of the 

 jheels, or shallow salt marshes, it is known to be in progress 

 of formation now, in thin layers. As the locality of the bore 

 formerly presented features similar to these, we obtain a 

 ready explanation of the occurrence of the kankar above 

 alluded to. It has long been one of the desiderata in Indi- 

 an geology to account satisfactorily for the existence of this 

 singular formation, and the favourite theory appears to be, 

 that it was derived from calcareous springs. That in some, 

 perhaps in many, instances this may have been the case, I am 

 not prepared to deny, but there are some of the phenomena 

 connected with the occurrence of kankar, which seem to me 



* Asiatic Society's Journal, vol. ii. page 649. 



