On the Structure of the Delta of the Ganges. 331 



Indian kankars are contemporaneous with the similar con- 

 cretions of the tertiary formations of England and France, 

 I only wish to exhibit the analogy existing between them, 

 as this may help us to some explanation of their origin. 

 The analogy might be extended to several other members 

 of tertiary formations, as the strata of the Isle of Wight, 

 in which Mr. Webster,* informs us both the nodular and 

 the flat form of concretionary limestone are met with, but 

 I would now proceed to offer a few remarks on the probable 

 origin of these substances. 



The forms effected by the nodules of kankar, and the 

 circumstances of their disposition in the clayey beds with 

 which they are associated,, have frequently been recorded by 

 observers as being strikingly similar to those of the flints in 

 the chalk strata, and it was these analogies which first led 

 me to suspect that the information we possess concerning the 

 origin of the one, might be made to bear upon that of the 

 other. From the state in which the fossils of the chalk strata 

 are found, many of them perfect in their most delicate details, 

 some of the shells preserving even their fine pearly lustre, 

 and the soft scales of fishes being often found beautifully pre- 

 served in the structure of flints, we are warranted in conclud- 

 ing that they were quietly entombed near the spots where they 

 lived and died, and that consequently no transporting power of 

 energy sufficient to bear from a distance the associated masses 

 of flint could have been in action upon them. We are thus led 

 to believe the flint contemporaneous, or nearly so, in its origin 

 with the chalk in which it is imbedded, and as the flint occa- 

 sionally passes imperceptibly into the chalk, the nodules of 

 the one near the line of junction being replaced by those of 

 the other, there is thus afforded an additional argument for 

 the flints having been formed in the places were they 

 are now found, and against their having been derived either 

 from silicious springs, or other sources, and brought from 

 * Geological Trans, vol. ii. p. 209. 



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