Abstract

Since the United States will eventually adopt the metric system, geologists should consider abandoning the nondecimal Udden-Wentworth-Krumbein (UWK) grade scale of particle sizes. Most of the advantages claimed for the UWK system also apply to other geometric grade scales that have an associated log-transform scale. The claim that the UWK major class boundaries are “natural” is not supported by the evidence and is irrelevant. A new grade scale is proposed with major grade boundaries at 0.01, 0.1, 1, 10, and so forth. An associated log-transform scale (the tau scale) is defined so that tau = 12 log10d/d0, where d is grain diameter in millimeters and d0 is 1 mm. The proposed scale has easily remembered grade limits and easily calculated log-transform scale, repeating numbers, major classes of equal interval, and good potential for international adoption and application in other fields.

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