The sides of the triangle described above set rigorous boundaries for effects associated with homogeneous saturation and patchy saturation at low frequencies or for situations in which frequency-dependent dispersion can be neglected. However, when the data do not in fact satisfy these assumptions of the theory, plotting the data this way provides an opportunity to observe and interpret deviations from the behavior predicted by the theory. For example, data which plot above the patchy saturation line represent excessively stiff rock. One possible cause of systematically high stiffness values is frequency-dependent dispersion (Biot, 1956a,b; Biot, 1962; O'Connell and Budiansky, 1977; Mavko and Nur, 1978; Berryman, 1981; McCann and McCann, 1985; Johnson et al., 1987; Norris, 1993; Best and McCann, 1995). Chemical effects, not taken into account in the analysis, might also cause measurements to deviate systematically from predicted behavior. For example, adhesive effects associated with chemical reactions between pore fluid and solid constituents might cause systematically high values. Another consequence of rock-water interactions is softening of intragranular cements. In this case, data for susceptible rocks would systematically plot below the Gassmann line at low saturations. Direct indications from elastic data of rock-water interactions [e.g., see Bonner et al. (1997)] may lead to new methods of determining other rock properties controlled by chemical effects, such as the tensile strength.