The Sand Gauge is a convenient chart for accurate and consistent determination of grain sizes. This flexible, waterproof, plastic card has actual sand grains for sizing and roundness classification. Chart includes size classification from silt to very coarse, roundness chart, bed thickness classification, field checklist, geologic time scale, and two carbonate classification charts. Gauge measures 2.5” x 3.5” and has nylon string for carrying convenience. Manufactured by W.F. McCollough.