1900 S. S. BUCKMAN — EXCURSION NOTES 187 



with the position of the Kennet in regard to the Avon. 

 The Kennet occupies the synclinal trough. Its posi- 

 tion and the eastern direction of the Kennet-Thames has 

 been largely determined by the position of the Pewsey 

 anticline. The diagram shows the possibility of the Avon 

 robbing the underground water from north of the Kennet. 

 How far this is applicable to the present case is a matter 

 for future work ; but the possibility of such river-robbery 

 in this or other cases is interesting. 



This diagram (Fig. 15), so far as ground levels were 

 concerned, was merely a rough sketch made after cycling 

 through the country ; but since it was drawn, and the 

 above notes were written, I have been able to work out 

 the question more fully. Unfortunately the maps of the 

 Geological Survey do not give contour lines, so the infor- 

 mation as regards contours has to be obtained from one 

 map, and that as regards geology from another, which is 

 not a satisfactory plan. 



However, I have now drawn a scale diagram of part of 

 the country, and have put in the geology according to 

 actual heights. The resulting diagram (Fig. 16), gives 

 the ground level contour, exaggerated on account of the 

 difference in horizontal and vertical scales ; but the relative 

 levels are correct. It will be seen that the valley of the 

 Salisbury Avon is, even near its head, lOO feet lower than 

 that of the Kennet, and that the springs supplying the 

 Salisbury Avon are below the level of the Kennet. 



The syncline beneath the Kennet valley really forms a 

 basin wherein the water which, both north and south of the 

 Kennet, falls on and mainly sinks through the pervious 

 Chalk, is held up by the partly impervious Greensand and 

 the very impervious Gault. And the water in this basin 

 can be held up to the line marked as " water level for 

 Salisbury Avon " — proved by this being the level of one of 

 the Avon's springs. 



