C. N. Edmonds replies

Abstract

The author thanks Mr E. J. Wilson for his comments. Wilson suggests that the background solution feature density for the various geographical regions on the Chalk outcrop, shown by Fig 1, cannot be explained geologically or climatologically. The greatly enlarged data base which is now available has not particularly changed the relative differences in solution feature density values for the regions. The pattern is therefore considered to reflect strongly the geomorphological evolution of the surface of the Chalk outcrop through Tertiary and Quaternary times. The major difference in land surface development between Chalklands of Yorkshire, Lincolnshire and East Anglia and those further south is that the more northerly areas have been glaciated. Glacial erosion has planed off the Chalk and removed the zone in which solution pipes would formerly have been present. Some truncated remnants of pipes, however, have survived, e.g. in the Syderstone area, Norfolk, Whitaker & Jukes-Browne (1899 p. 77). The Chalk is often piped beneath Tertiary cover deposits and many localities are recorded where swallow holes are concentrated along the feathering margins (see, for example, Fig. 2. Chiltern Hills region). Most of the higher background solution feature density regions contain extensive areas of Tertiary cover deposits. Commonly groundwater is concentrated into rivers and streams on these deposits which are acidic and when they reach the Chalk dissolve it. The low background solution feature density regions are generally devoid of such cover deposits or else surface drainage is dominated by rivers and streams flowing off the Chalk onto