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PHYSIOGRAPHY. 



fCHAP. 



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Perhaps the term "basin," just used, is 

 one which is hkely to mislead unless properly 

 qualified. It is true that, if you go north 

 from any part of the valley of the Thames, 

 you find yourself sooner or later travelling 

 up-hill, and therefore reach higher ground 

 than that through which the river flows ; if 

 you travel southwards you do the same thing ; 

 while towards the west, the ascent is not less 

 marked. The river then really does occupy 

 a hollow, inclosed on three sides by high 

 ground. But, it must be borne in mind, that 

 this hollow is nothing like the deep hollow 

 associated with our ordinary notion of a 

 basin ; it is, in fact, so slight a depression 

 that it would perhaps be better to speak of 

 the " dish " of the Thames rather than of its 

 "basin." In Fig. 5 the undulating line indi- 

 cates the general contour of the surface of the 

 country along a north-and-south line drawn 

 across the basin of the Thames, from the 

 Chiltem hills on the north, to the North 

 Downs on the south. The very gentle curva- 

 tures of this line show the extreme shallow- 

 ness of the so-called basin ; and also show 

 the irregularities in the form of the ground. 

 Although the opposite north and south hills 

 may attain to a height of several hundred 

 feet above the river, yet the distance be- 

 tween them is so great, amounting to some 

 fifty or sixty miles, that the rise from the 

 river to their summits would be almost in- 

 appreciable in a diagram brought within the 



