Discussion

Abstract

Mr B. Waugh said that for the past two years he had been examining by electron-microscopy the surface textures of sand grains, especially sand grains collected from modern desert and beach environments. The criteria used by the authors for distinguishing environments of deposition from distinctive surface textures were directly comparable with his results. In a study of the surface textures of sand grains from the Penrith Sandstone of the southern part of the Vale of Eden where the rock was poorly compacted, and from the Basal Yellow Sands of County Durham, electron micrographs showed the surface of the grains to be covered in conchoidal fractures, rounded abrasion-blocks, and percussion-marks (Waugh 1965, Proc. Yorks. geol. Soc. 35, 59–69). These were features of an aeolian abrasion process, and confirmed the accepted aeolian origin of these two deposits. Dr F unnell replied that it was gratifying to learn that Mr Waugh had found the suggested criteria applicable to his own results, and Mr Waugh’s confirmation of the mode of origin of the Permian occurrences by this means was most interesting. Mr W. B. H arland suggested that the evidence of glacial attrition of sand grains might not necessarily denote a glacial environment if a similar grinding process could also be shown to take place, for instance, in a mud-flow. On the other hand, it seemed that glacial action, in the sense of ice rafting, might well produce a till, possibly with little evidence of attrition of the sand grains in it unless most of