FORMATION OF LAND. 211 



a beach. The gravel in the valley of the Thames, for 

 instance, which we find in the most elevated parts of 

 that valley, as at Wimbledon Common, and Hampstead 

 Heath, contains no stone but that very same flint, which at 

 a distance from the river, or even near it, as in the county 

 of Kent, is contained in the chalk formation ; but while 

 the pieces of flint that are found in the chalk are an- 

 gular, and covered with a rugged crust, those in the 

 gravel are all, more or less, rounded ; and they have 

 been rounded by rubbing against each other in water, 

 as the hollows in them, which could not be so easily 

 rubbed, have still the same rough surface as those 

 found in the chalk. It is therefore impossible to 

 avoid coming to the conclusion, that the gravel in the 

 valley of the Thames has been formed out of the chalk 

 soil, and formed too by the action of water ; nor can 

 we easily suppose that that water has been any other 

 than the sea ; because, the gravel has a principle of 

 adhesion, which is not found in the gravel of rivers. 

 Great part of the connecting matter in the binding 

 gravel, is the powder of flint, just in the same manner 

 as in that which does not bind ; but it also contains a 

 quantity of salts of lime, which it could have derived 

 only from the impregnation, by the sea, of a portion of 

 the original chalk ; and to that it owes its adhesive 

 nature. But wherever the river has continued to wash 

 it, those salts of lime have been decomposed and 

 floated away, and the flint-dust has been left loose. 

 The very same happens if we expose a heap of the best 

 " binding " gravel to the action of rain for a sufficient 

 length of time ; it loses its adhesiveness, and becomes 

 loose. Thus it is evident, that the gravel Jias been 



