Letter | Published:

The Geological Time-Scale


SINCE my communication on this subject was written1, much has happened. Prof. J. L. Kulp2 has just published a time-scale in which the duration of the geological periods is given as follows: Ordovician, 490–430 m.y.; Silurian 430–410 m.y.; Devonian 410–355 m.y.; Mississippian 355–330 m.y.; Pennsylvanian 330–275 m.y.; Permian 275–220 m.y.; Triassic 220–180 m.y.; Jurassic 180–135 m.y.; Cretaceous 135–70 m.y. An almost identical geochronology (±5–10 m.y.), awaiting publication, was communicated to me privately by Prof. A. Holmes3 a month ago. The Oxford age of 305 m.y. for Dartmoor granite (by potassium/argon assay on biotite) has been confirmed by Dr. H. Faul4 of U.S. Geological Survey (292 m.y. and 288 m.y. on the same rock by the same method). A full isotopic assay of Hercynian pitchblende from Geevor, Cornwall, has yielded to Dr. A. G. Darnley5 of the Geological Survey of Great Britain a comparable date of 288 m.y. From all this it is confirmed that an extension of the Holmes B time-scale is called for, and that the best values are, as one would expect, a little higher than the averages of the experimental results published previously1. There is however, no support from recent researches for the conclusion that the Lower Cambrian is older than 600 m.y.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1

    Nature, 184, 1310 (Oct. 24, 1959).

  2. 2

    Kulp, J. L., Program 1959 Annual Meeting, Geol. Soc. America (Nov. 2, 1959).

  3. 3

    Holmes, A. (personal communication, Oct. 6, 1959).

  4. 4

    Faul, H. (personal communication, Oct. 1959).

  5. 5

    Darnley, A. G., Geol. Surv. Great Britain, Age Determination Rep., 6 (Aug., 1959).

Download references

Author information

Rights and permissions

Reprints and Permissions

About this article


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.