We thank Dr. Coleman very much for his kind reception of our paper and for comments on our ambiguous remarks concerning the iron mineralogy of the sandstones. X-ray evidence was unfortunately limited to samples at outcrop from a single locality and results show haematite as the only crystalline iron mineral present. This was a ‘spot sample’ and we do not wish to imply that this evidence in any way characterises the overall aquifer mineralogy. However, field observations and microscope studies on outcrop and core material indicate a wider range of iron minerals which we identify as goethite, pyrite and limonite (as defined by Dr. Coleman). In the absence of confirmatory X-ray and chemical analysis therefore we speculate to some extent on the composition of the cement of the sandstones. In two further papers on this subject (in preparation) dealing with the East Midlands and South West England Triassic Sandstones we investigated the relationship between groundwater geochemistry and sandstone mineralogy in more detail and these results will be reported in due course.
In the meantimes we would like to draw attention to a recent paper by Schluger & Roberson (1975) who deal in some detail with the relationship between colour of sediments, mineralogy and groundwater chemistry of the Patapsco Formation, Maryland.
- © The Geological Society, London 1977