A COMMUNICATION from Mr. A. S. Barnes traverses the arguments put forward by Mr. J. Reid Moir for the human origin of the pre-Crag implement (see NATURE of January 28, p. 151) and deals seriatim with the characters upon which he relies. The problem of the differences between natural and human flaking is discussed by Mr. Barnes at length in the current issue of the American Anthropologist (41, 1, 1939, p. 99). He there maintains that the arguments for the human origin of pre-Crag implements are for the most part purely subjective, while it has been shown that purely natural forces are able to produce flaking similar to that on eoliths, and further, that the flaking on eoliths differs from that on human work. Although attempts have been made to formulate objective differences between the flake detached by man and those detached by natural agencies, such as ‘resolved flakes’ and flakes owith certain other characteristics, these effects, Mr. Barnes holds, are found on flake fractures by fortuitous pressure as well as by man. After recapitulating the factors operating in natural and artificial fracture, Mr. Barnes goes on to suggest that a criterion of human workmanship, readily measurable and common to both classes of flaking, natural and artificial, is to be found in the angle platform-scar, which he defines as the dihedral scar formed by the intersection of the surface on which the blow has been struck, or pressure applied, and the surface of the scar left by the flake removed. As the result of an investigation of a large number of specimens by this method it has been found that an industry, or supposed industry, may be regarded as of human origin if not more than 25 per cent of the angles platform-scar are obtuse, that is, 90° and over. None of the eoliths examined by Mr. Barnes complies with this criterion, and, he maintains, cannot therefore be considered to be of human origin.