Large-scale superficial structures in the Northampton Ironstone Field

From Major J. C. McM ath , B.Sc. F.G.S. :— The authors are to be congratulated on these detailed researches and conclusions, with their interesting economic implications. The work emphasizes afresh the great caution necessary in the interpretation of tectonics generally and it is clear that a revision of much structural and stratigraphical work is required in the light of the authors' results. It can be expected that wherever strata of strongly contrasting competency under load occur analogous phenomena may be found. Features similar to those described in the paper, though on a much smaller scale, have been observed by me in the lateritic areas of Lake Province, Tanganyika Territory, particularly in the Saragura and Mawe Meru areas to the south-west of Lake Victoria. “Dip-and-fault” structure, together with cambering, were noted especially on the lateritic flats abutting on the Rhino and Mabubi rivers. The features were developed a short distance from, and parallel to, the courses of these streams, and they faded out where the laterite was of little thickness or where it directly overlay the igneous country rock. The structures were best seen where the laterite was over eighteen inches in thickness and was underlain by ferruginous earth or clay (uncemented decomposition products of the country rock). Both “dip-and-fault” structure and cambering could also be seen on a very minor scale in old prospecting trenches where these were of some size. No “valley bulging” was observed. Authors' reply :— The authors write that they recognize that, as observations accumulate from a