Stones which have a low mechanical strength and which are prone to dissolve with high porosity are likely to adjust or change rapidly upon exposure. These stones are likely to be degraded very rapidly as they adjustto their conditions of exposure. Stones that are less porous, less soluble will respond more slowly to their conditions of exposure, thus they will exhibit less degradation and not tend to reflect the prevailing exposure conditions. The latter group may retain more memory, more former surface forms and more weathered products, and so will always be unadjusted to prevailing conditions. This means that a wide range of degradational forms may be present upon a single building. Those present on each surface will reflect the relative degree of adjustment to contemporary conditions and the expression of the underlying characteristics of the stone.