330 On the Structure of the Delta of the Ganges. 



position. Detritus of such an origin is invariably mixed, and 

 contains specimens of the different materials which the force 

 of the transporting agent was capable of bearing along. 

 The shooting of branches and the gradual passing of the 

 kankar into the clay above and below, seem farther to mili- 

 tate against the idea of the operation of powerful, or even 

 any, transporting agency. It has been said, that the kankar 

 of India has no analogous formation in the world ; but I con- 

 ceive this to be doubtful, as it is known that the London 

 clay* contains numerous contemporaneous nodules of hard 

 marl or clayey limestone, which occur in regular horizontal 

 layers at unequal distances, usually varying from four to forty 

 feet apart. These nodules are called Septaria, from their 

 being divided by partitions or veins of calcareous spar, and 

 in their cavities are frequently found crystals of calcare- 

 ous spar (carbonate of lime) and heavy spar (sulphate of 

 baryta.) The Septaria are surrounded by crusts which con- 

 tain a smaller proportion of lime than the central parts ; and 

 of the Ghazipoor kankar, Mr. Everest remarks similarly that 

 its cavities are lined with crystals, and that while the fresh 

 fracture is of a brownish grey colour, exhibiting the stone 

 compact, the exterior is covered with a white or yellowish 

 white crust. The chemical composition of the Septaria 

 of the London clay is identical with that of the Ghazipoor 

 kankar, consisting chiefly of carbonate of lime with silica, 

 alumina and oxide of iron, or slightly ferruginous clay, and 

 the natural cement stones of Harwich, Sheppy, and other 

 places, are used for the same purposes in England as the 

 kankars are in India.f In the tertiary basin of Paris si- 

 milar tuberose masses are found in the clayey and calcare- 

 ous marl of the fifth and sixth formations. % It is scarcely 

 necessary to remark, that I do not mean to contend that the 



Cinder's Theory of the Earth. t Pasley on Cements, and Note. C. 



% Cuvier's Theory of the Earth. 



