Response to Owen, H.G. (2014), discussion on “Aldiss, D.T., Under-representation of faults on geological maps of the London region: reasons, consequences and solutions” [Proc. Geol. Assoc. 124 (2013) 929–945]

I thank Dr. Owen for his comments on my paper (Aldiss, 2013) and for his useful exploration of several aspects of the tectonic development of the London region. I am especially grateful for him drawing attention to his evidence for Quaternary faulting of the Gault in the south London area, and to several other pertinent and useful papers, notably Lake's (1975) discussion of the tectonics of the Weald and those by Owen, 1971 and Owen, 2012. However, I feel that his remarks mainly concern topics that are beyond the scope of my paper. My paper was not about the ‘distribution of current faults in the London region’, as much as being about the current understanding of the distribution of faults in the London region. I was not attempting to demonstrate that the London region has, in reality, been tectonically inactive nor that no faults have been recognized in the area – only that faulting is greatly under-represented on the local geological maps. In introducing this topic briefly, it appears that I have perhaps described the tectonic development of the region in an over-simplified manner. Also, it would have been useful to emphasize the distinction, within the term ‘tectonic activity’, between regional crustal uplift and subsidence (which may or may not be accompanied by faulting, and which is not directly relevant to the main subject of the paper) and fault displacement, either vertical or lateral. However, my principal point remains the same: few faults are shown on geological maps of the London area and this is both a consequence of and a contributory cause of a perception that the London Platform is an area of long-term relative crustal stability, compared with the Weald Basin

Geological mapping of the Late Cretaceous Chalk Group of southern England : a specialised application of landform interpretation

The modern Chalk Group lithostratigraphy divides the Chalk of southern England into nine formations, each with a characteristic lithological assemblage. It is more useful than the traditional subdivision into Lower Chalk, Middle Chalk and Upper Chalk because it can be applied more consistently over a wider area, it provides a better indication of lithological variation, it allows the recognition of more tectonic structures and it is thus more useful for practical application in engineering geology and hydrogeology. The process of surveying the Chalk that has been developed by the British Geological Survey over the past two decades is an empirical modification of the traditional methods used for detailed geological survey of sedimentary sequences in other parts of the United Kingdom. Each Chalk formation is closely associated with characteristic landforms, allowing them to be mapped with reasonable consistency and accuracy in largely unexposed ground and through built-up areas. This association of landform and lithostratigraphy reflects the response to weathering (and other surface processes) of relatively subtle variations in bulk lithological assemblage, rather than of individual beds of contrasting lithology