67 



these remains with another thick coating of stalagmite ; such altera- 

 tions might even be several times repeated. 



The annexed sketch will explain this case more clearly : 



Fig. 7. 



The great geological law, that the order of succession of strata in- 

 dicates the order of their antiquity, the lowest being always the 

 oldest, is limited by the condition that those strata shall not have 

 been removed from their original beds. 



But the action of causes still existing may have produced apparent 

 deviations from this order, and the present state of geological science 

 seems to require an examination of such exceptional cases. 



If a great river, similar to the Mississippi or the Amazon, flowed 

 through a country whose superficial stratum consisted of a thin bed 

 of chalk succeeded by gault, then during thousands of ages it 

 would distribute, by means of an ocean current, its milky burden 

 over the bottom of the existing ocean, on which, after a lengthened 

 interval, a bed of chalk would reappear. 



When the superficial bed of chalk over which the river flowed 

 was cut through, its waters would begin to act on the newly-exposed 

 gault ; and after another period of equally vast length, a stratum of 

 gault might cover the chalk, thus producing an extensive inversion 

 of the two strata. 



But this would be dependent on the relative fineness and specific 

 gravity of the particles of the two substances. It is possible that 

 the particles of gault, if larger or of greater specific gravity than 

 those of the chalk, might arrive at a greater terminal velocity, and 



