532 A. J. Jukes-Browne — Solution in Valley-making. 



to look back to the time when the present basset-surface of the Lower 

 Oolites was entirely covered by Oxford Clay, and when the outcrop 

 of the underlying limestones lay further north across the Banbury 

 district ; doubtless also forming higher ground than the plain of 

 Oxford Clay. Such must certainly have been one phase in the 

 gradual development of scarp and valley during Tertiary time. 



Surely it is more reasonable to regard these courses of the Glyme 

 and the Evenlode as valleys which originated on a clay-cover in the 

 usual manner, and have been incised into the underlying limestones. 

 I feel sure that in this new theory the cart has been put before the 

 horse, and that the whole valley-system of the Oolitic plateau was 

 formed in the ordinary way by the mechanical action of rain and 

 running water long before the plateau was reduced to its present 

 condition ; but there can be little doubt that some of the features 

 which the valleys now exhibit are attributable to the chemical action 

 of the water which runs into the waterways and sinks underground. 



In brief, my conviction is that the valleys have swallowed the 

 ancient watercourses, and that it was the latter which determined the 

 courses of the subterranean streams, and not any hypothetical system 

 of joint-planes. It is quite possible that under present conditions 

 more material may be annually removed by chemical solution than by 

 mechanical erosion, but I do not think that solution would be specially 

 active along the valleys unless they had been previously formed by 

 surface-erosion. On this view it is easy to unclerstand why there is 

 only one valley-system, but if Mr. Spicer's theoiy were correct we 

 ought to find traces of an ancient system of mechanically-formed 

 valleys which did not coincide with the subsequently-formed 

 ' solution -valleys.' 



In another paper ' Mr. Spicer has applied his theory to the valleys 

 of the Chiltern Hills, and Mr. F. J. Bennett has independently evolved 

 a similar theory in explanation of certain interrupted valleys which 

 traverse the Hythe Beds of Kent.^ 



Mr. Spicer remarks that " the strongly marked Chiltern valleys run 

 in various directions, but they are in the main joint- valleys. There 

 are no heights sufficient to produce them by superficial denudation, 

 there are no alluvial fans showing the results of underground 

 action . . . They are too varied in trend and too marked in 

 character to be due to any possible cause that can be logically 

 suggested, except one, but they display universally the characters 

 and results that would naturally arise from the percolation of 

 acidulated water through rock so easily soluble . . ." 



This seems to me an extraordinary series of statements. How can 

 valleys which run in various directions be "in the main joint- 

 valleys"? In my opinion their arrangement is that of a natural 

 system of surface rainfall drainage, and Mr. Spicer quite ignores what 

 I have written about the former extent of a clay-cover (i.e. the Clay- 

 with-flints) all over this region. Why he should expect to find 

 * alluvial fans ' I do not understand, nor why (if present) they can 



1 Geographical Magazine for September, 1908, p. 288. 



2 Op. cit., p. 277. 



