﻿Vol. 64.] SOLUTION- VALLEYS IX THE GLTME AREA. 341 



ordinary power, and the base-level of solution will not be 

 reached until all the chalk and limestone have disappeared. 



One further striking piece of evidence of the removal of material 

 nndergronnd is found in the gaping fissures often noticed in the 

 quarries on the plateau around the Evenlode watershed, near Stow- 

 in-the-Wold and Moreton-in-the-Marsh, where the limestone-bands 

 appear to be stretched and shattered in a manner that has often 

 been commented upon, but never, so far, explained. This dis- 

 integration of the limestone is seen in a less degree in the area 

 under consideration. 



Further evidence of local disintegration is given in the recently- 

 issued Memoir of the Geological Survey accompanying the Oxford 

 Sheet (1908), where on p. 107 it is stated that 



' the two principal consequent rivers of the district [that is, the Evenlode and 

 the Cherwell] have eroded their channels along downfolds of the strata.' 



The evidence supporting this is quoted thus: — 



'In the case of the Evenlode the Glreat Oolite strata incline slightly up- 

 wards from the river on the Combe side and on the Long Hanborough side.' 



"Without questioning the probability of simple downfolds trending 

 in two such remarkably different directions along an elsewhere almost 

 uniform dip-slope, it may be said that this sudden sag at the edge 

 of the valleys, which is easily seen at Enslow Bridge (and appeared, 

 when I observed it, to be no more than a slight down-turning of 

 the straight edges of the strata above the river- valley), illustrates 

 the way in which superincumbent strata sag when support is locally 

 removed by underground solution. The view of the memoir in 

 question appears to be that the Evenlode cut ' the winding gorge 

 west of Hanborough,' and is ' a perfect example of erosion by a 

 meandering river' (p. 112). On the other hand, the suggestion 

 intended to be conveyed by this paper is that an Evenlode 

 Mississippi is unnecessary. Something brought Triassic pebbles 

 into the Evenlode ; but, since the morphology of that river is 

 accurately represented in the Glyme area, which is absolutely free 

 from any drift, it is suggested that the drift used the Evenlode 

 Yalley precisely as a waggon uses a road. 



The main valleys in this region are approximately dip-and-strike 

 valleys, but the term 'joint-valleys' may perhaps be applied to 

 them. Percolating water will reach a master-joint or a series of 

 master-joints, and dissolve out a winding course underground. 

 The water from the neighbouring joints will gradually tend to leak 

 into the master-joint line, and thus a winding area of weakness 

 will be established which tends continually to widen. The ground 

 above this weakened line will slowly subside, and at length the 

 weakened material will be entirely removed, exposing the stream. 

 The young stream will flow — as it does — in a valley with the 

 contour of a dry valley ; but, as the banks gradually dissolve away 

 farther from the main stream, the widened valley-floor will become 

 choked by solution-debris mingled with fine flood-sediment. This 

 will form a level flood-plain from bank to bank, over w^hich the stream 

 will wander helplessly, except when it is merged in a broad area 



