Extract

In their pertinent account of the Walton's Wood slide the Authors show that slip surfaces have probably been subject to subsequent chemical reduction at some period during the time interval, Late-Glacial to Present. As they point out, the much lower In their pertinent account of the Walton's Wood slide the Authors show that slip surfaces have probably been subject to subsequent chemical reduction at some period during the time interval, Late-Glacial to Present. As they point out, the much lower Fe203 content of the shear zone material (Table 4) is convincing supporting evidence. content of the shear zone material (Table 4) is convincing supporting evidence.

Work in connection with unburnt colliery spoil heaps implies that significant low temperature chemical changes involving clay-minerals in Coal Measures rocks are unlikely to be short-term processes (for example, Spears et al., 1971). A recent study of Spoil Heap No. I at Littleton Colliery, Staffordshire suggests that chemical and mineralogical differences between a recently exposed failure surface (probably reactivated) and other, non-burnt, spoil samples are very minor indeed. Here again, this is in the short-term since the original failure probably took place about 25 years ago and is certainly not more than 50 years old.

Quantitative X-ray mineralogical analyses are somewhat restricted in accuracy as implied by Early and Skempton (p. 29). However, quartz determinations by X-ray methods are usually reasonably accurate, and a high degree of precision is expected in chemical analyses. It is therefore of interest to consider both sets of Walton's Wood