148 PHYSIOGRAPHY. [chap 



enormous. At Kingston, as has been stated at p. 126, the 

 dissolved matter is estimated at about 548,230 tons per 

 year. Now reckoning 15 cubic feet to the ton, which is 

 about the average weight of chalk, this weight is equivalent 

 to upwards of 8 million cubic feet. But this is only at Kings- 

 ton, and it is certain that much more is dissolved before the 

 river reaches the sea. Nor must we forget to add some- 

 thing considerable to represent the quantity of coarse sedi- 

 ment pushed along the bed of the river. On the whole, 

 then, we shall probably not be far wrong in saying that 

 the Thames carries down to the sea, every year, 14 million 

 cubic feet of solid matter. 



Imagine a huge die-shaped mass of stone measuring 100 

 feet in length, 100 feet in width, and 100 feet in height : 

 this would contain one million cubic feet. No fewer, then, 

 than 14 of these gigantic cubes appear to be quietly stolen 

 from the surface of the Thames basin by means of running 

 water, and transported to the sea, in the course of a single 

 year. But the Thames basin covers a very large area, and 

 ,it will be found on calculation that, admitting the abstraction 

 of this vast mass, the entire surface of the basin would be 

 reduced in level by only ^-^th part of an inch every year. 

 At the present rate of wear and tear, therefore, denudation 

 can have lowered the surface of the Thames basin by hardly 

 more than an inch since the Norman conquest ; and nearly 

 a million years must elapse before the whole basin of the 

 Thames will be worn down to the sea-level. This method 

 of showing the amount of work effected by rain and rivers 

 in wearing away the land was suggested by Mr. A. Tylor, 

 and has since been applied with interesting results by other 

 geologists. Thus, Prof. Geikie has calculated' that, at the 



" On Modern Denudation." By Archibald Geikie, F.R.S. Trans- 

 actions of the Geological Society of Glasgow, vol. iii. ]"). 153. 



