This date list reports samples completed before 1979. Methods, equipment, and techniques were reported previously (R, 1968, v 10, p 246; R, 1970, v 12, p 87). Age calculations are based on the conventional 14C half-life of 5568 years. The working laboratory standard is 95% of the NBS oxalic acid standard (SRM 4990). Results are reported in years before 1950 and the standard deviation is based on counting statistics of sample, background, and modern standard. Corrections for δ13C are not included.

This list contains most of the measurements made during 1980, since our last list (R, 1981, v 23, p 33-37). A second methane synthesis unit became operational (Dauchot-Dehon and Van Strydonck, 1979) at the end of 1979. Basically, this unit is the same as the one built earlier (Klebert and Heylen, 1966).

The following list contains samples of geologic interest that were processed from February 1974 through May 1980 at the Illinois State Geological Survey (ISGS) Radiocarbon Dating Laboratory. The archaeologic samples processed during the same period will be published in our next date list. The benzene liquid scintillation technique was used following laboratory procedures previously reported by Coleman (1973; 1974).

Most of the 14C measurements reported here were made between October 1979 and October 1980. Equipment, measurement, and treatment of samples are as reported previously (R, 1968, v 10, p 36-37; 1976, v 18, p 290; 1980, v 22, p 1045).

The following radiocarbon dates are a partial list of samples measured for a variety of projects and materials since August 1980. Chemical and counting procedures remain the same as indicated in R, v 20, p 274-282.

The following radiocarbon date list contains dates of samples measured since our previous list (R, 1979, v 21, p 131-137). As before, age calculations are based on the Libby half-life 5570 ± 30 yr and reported in years before 1950. The modern standard is 0.95 of the activity of NBS oxalic acid. Sample pretreatment, combustion, and counting technique are essentially the same as described in R, 1971, v 13, p 135-140, supplemented by new techniques for groundwater processing (R, 1979, v 21, p 131-137) and for soil sample treatment (R, 1977, v 19, p 465-475).