Chalk and Flint Formation. 39 



It may, in passing, be mentioned that in tree 

 branches converted, without doubt by aqueous in- 

 filtration, into sulphuret of iron, which are found in 

 a sandy bank beside the landslip near Folkestone, 

 and occasionally washed up by the sea there, the 

 interior fibre is microscopically perfect. I have 

 also a similar specimen said to be from a deep cut- 

 ting near Dover ; and many small specimens of the 

 same description are gathered at Gravesend. 



But I do not go into that portion of the subject, 

 beyond pointing out that it is not to be mixed 

 up with the question of the origin of the flint 

 and chalk formation ; nor ought it even to be 

 assumed that all chalcedonic and quartzose forma- 

 tions admit of the same explanation with one another, 

 or are necessarily all aqueous in their formation if 

 some may prove to be so. 



In conclusion I may briefly indicate two inferences, 

 which perhaps may already have spontaneously 

 suggested themselves. 



First, considering the vast extent of the chalk and 

 flint formation, it is manifest that had it all fallen 

 upon the earth at one time, it might have materially 

 affected the earth's balance. But, coming by degrees 

 at successive periods, the balance might adjust itself 

 by a flow of the waters of the sea to the opposite 

 part of the globe where the weight had to be counter- 

 balanced. This receding of the waters would have 

 the effect of a rise of the chalk above the level of the 

 sea, such as has actually occurred; or, which is 

 equivalent, a subsidence of the sea-level relatively to 

 the chalk. On the other hand, the gradual accumu- 

 lation of a vast mass of compensating waters at the 

 opposite side of the world, might, by its superin- 

 cumbent weight, at last break down the underlying 



