The London Clay is well known as an engineering material and it is probably the most publicized example of a stiff fissured clay. Recently, growing interest has been shown in the small-scale structural discontinuities of this clay and their effects on the engineering behaviour of the material. The paper deals with observations of small discontinuities (or fissures) at sites in the London and Hampshire Basins. Orientation data from the various sites are plotted and analysed in the form of stereographic projections. The size and form of the discontinuity surfaces are considered and their distribution related to orientation and possible modes of origin. Both orientation and surface forms of discontinuities are related to the regional structure of the clay and adjacent sediments, and it is tentatively concluded that the general trends of discontinuity patterns in local areas, the local regional structure, and geological history can be correlated.