CHAPTER XVII. 



THE GEOLOGICAL STRUCTURE OF THE BASIN OF THE THAMES ; 

 AND THE INTERPRETATION OF THAT STRUCTURE. 



In the preceding chapters, the general character of tlie 

 River Thames and the form of the surface which it drains, 

 have been considered ; its waters have been followed to the 

 sea, and, thence, by way of the atmosphere, back to that 

 surface ; while the atmosphere, and the waters of the land 

 and sea, have been traced back to the elementary bodies of 

 which they are composed. The river, and the rains which 

 feed it, were next considered as a grinding and dissolving 

 machinery, by which the surface of the Thames basin is 

 being insensibly worn away and its materials carried down 

 to the ocean ; while the sea, so far as it washes the banks 

 and shallows of the estuary and of the adjacent coasts, was 

 shown to be a no less persistent destroyer of the dry land. 

 And then, seeing that all rivers and all oceans are engaged 

 in the business of denudation and dissolution, it became a 

 matter of interest to discover what natural operations, if 

 any, tend to compensate this constant wear and tear of the 

 dry land. Such compensating agents were found in the 

 forces which tend to raise submerged land ; in volcanoes, 

 which transfer fluid matter to the surface, where they 



