N. J. Hancock writes: I regard the term 'pressure solution' as one of the most misused in the science of geology. A far better term is 'dissolution' or perhaps 'grain margin dissolution'. This is because the phenomenon shows no significant relation to pressure as reflected by depth of burial. Pressure is involved only insofar as dissolution will not take place at zero overburden pressure, and as the principal development of sutured contacts does occur in the direction of maximum stress (usually top and bottom of detrital grains in oriented samples). At only modest depths of burial, dissolution may take place; whether or not it does so is highly variable, and other factors are therefore much more important.

In my view, dissolution at grain boundaries is controlled principally by pore fluid chemistry, and also by boundary layer catalysis. In the latter context, Blanche & Whitaker's (1978) description of clay layers at grain boundaries undergoing dissolution is most welcome. These clay layers are almost invariably present, and they probably play a key role in retaining water which allows the removal of dissolved material by diffusion. In addition, the cations within the clay (which is usually illitic) may help to promote the suitable pore

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