Details are given of trial pits which have been excavated during site investigations carried out in Kent and Oxfordshire over the past two and a half years. Slip surfaces have been found to a depth of 15 ft below the existing ground-level on slopes of stiff fissured clay, where the slope angles are 3° and steeper. It is suggested that, whilst these slopes are stable under present day conditions, the slip surfaces must have been formed as the result of periglacial activity. The presence of these discontinuities, which have shearing resistances at or near their residual values (Skempton 1964), is the governing factor affecting the maximum possible natural slope angle and also the stability of any engineering works that may be constructed in the area.
In the case of the investigations in Kent it has been possible to recognize three separate periods of solifluction corresponding to the Saale Glaciation, the Main Weichselian and Zone III of the Late Glacial.