324 ReporlH and Proccedinga — Geological Society of London. 



l.—May 6tli, 1908.— Professor W. J. Sollas, Sc.D., LL.D., F.R.S., 



President, in the Chair. 



The following communications were read : — 



1, " Solution Valleys in the Glyme Area of Oxfordshire." By the 

 Eev. E. C. Spicer, M.A., F.G.S. 



A triangular area whose sides are defined by the converging 

 Evenlode and Cherwell with a strike valley, containing the up^ier 

 Swere for its base, contains a smaller triangular area defined by the 

 confluent Glyme and Dorn. This area is part of the gently tilted 

 Great Oolite limestone plateau, which is indented by a number of 

 sunken valleys running in various directions, principally with a strike 

 and dip trend, that show no marks of erosion but appear to be 

 subsidence valleys. They begin suddenly at any part of the area, 

 and descend with sinuous curves to a main valley into which they 

 open quietly without disturbing the main valley's contour, and 

 without bringing any surface debris. The main valley likewise 

 enters a stream valley in a similar manner. The stream valley 

 quietly develops into a broad sinuous river valley, with a floor, level 

 in transverse section, over which a small river stream aimlessly 

 meanders with the Evenlode characteristics. A gradation is shown 

 from the plateau dry valleys to the meander valleys, which are 

 sometimes flooded from bank to bank with soakage water. The 

 plateau area is quite free from drift or gravels, and from any of 

 the usual marks of surface denudation, although the valleys have 

 strongly marked cross sections. There are no marks of marine 

 currents, of fluvio-giacial scour, or of ice. There are no wind-gaps 

 suggesting beheaded streams, nor any evidence of vanished heights 

 that could produce tori'ents sufficiently strong to carve out the present 

 surface. At the mouths of several of these dry winding valleys issue 

 streams strongly impregnated with carbonate of lime. It is suggested 

 that percolating water forming an underground course along joint 

 lines removes enough material in solution to weaken a long, narrow, 

 winding area over which the surface subsides until the underground 

 stream is revealed. Solution then constantly widens the stream 

 banks into bowls of soakage, and leaves insoluble material to build 

 up a broad, level valley floor, which rises gradually above and 

 obscures the dry valley outlet streams, these then forming marshes. 

 It does not appear possible to reconstruct any local conditions that 

 could have produced these valleys by mechanical erosion, and it is 

 suggested that they are formed bj^ underground solution, and are 

 therefore called joint valleys or solution valleys. Prestwich (Quart. 

 Journ. Geol. Soc, vol. xxviii, 1872, p. Ixvii) estimates that 140 tons 

 of carbonate of lime are annually removed from every square mile 

 of the limestone area drained by the Thames. This would give an 

 annual amount removed by solution from the small Glyme area of 

 over 10,000 tons. 



