Summary

The Early Palaeozoic is the most difficult portion of the time-scale to calibrate due to the low number of precise calibration points although knowledge has greatly increased during the last few years. Thus, two-thirds of the data selected by McKerrow et al. (this volume) had not been published in 1980. These new data permit a reassessment of the preceding proposals. The location of some boundaries is still somewhat subjective; this explains differences in recommended or preferred numbers proposed by different authors. However, the correct assessment of the available data by the different authors allow one to define intervals of time (better than just numbers), and some sort of 'non disagreement' is now obtained which was not the case earlier. The present comment intends to show the points of agreement, to underline some differences of interpretation, and discuss some data not considered by McKerrow et al.