The American Commission on Stratigraphic Nomenclature is affiliated, as an active member representing Canada, Mexico, and the United States of America, with the International Subcommission on Stratigraphic Terminology of the International Commission on Stratigraphy. At the 19th annual meeting of the American Commission, Miami Beach, Florida, November 19, 1964, it unanimously voted to recommend that the following report, "Definition of Geologic Systems," from Circular 15 prepared by the International Subcommission on Stratigraphic Nomenclature (Hollis D. Hedberg, Editor) be submitted to the Executive Bureau of the International Commission on Stratigraphy for approval for publication. This recommendation was transmitted to the International Commission, although not received in time for recording in the report as published in "International Geological Congress, Report of the twenty-second session, India, 1964, as Part XVIII, International Subcommission on Stratigraphic Terminology, Definition of Geologic Systems."

It was also unanimously voted at the 19th annual meeting of the American Commission that, if possible, the report be reprinted as a Note of the American Commission on Stratigraphic Nomenclature to make it more generally and readily available to stratigraphers. The Commissioners agreed that the report is a great step forward in the understanding of the definition of geologic systems and that the delineation of the differences between biostratigraphic and chronostratigraphic units is especially good.

With the approval of Professor St^phgrrmer, President of the International Commission on Stratigraphy, and B. C. Roy, Secretary General, twenty-second session, International Geological Congress, "Definition of Geologic Systems" is reprinted here including the Foreword by Hollis Hedberg, President, International Subcommission on Stratigraphic Terminology, and with corrections by Hedberg of some typographical errors in the original printing. Footnote numbers are the same as in the original printing. The record of votes of the members of the International Subcommission and the comments of members opposing publication that are referred to in the Foreword are not reprinted here. These comments, by the Interdepartmental Stratigraphic Committee of the U.S.S.R. and by the Geological Survey of the Republic of South Africa, may be found in the report as printed by the International Geological Congress.

Reports of the American Commission express recommendations of stratigraphic practice endorsed by the Commission as of the date of publication. Notes are proposals and recommendations to the Commission and present data that bear on problems under study; they are presented for general consideration without endorsement. Notes published by the American Commission include the minutes of the annual meetings. Discussions are freely contributed comments on Reports and Notes.

Free copies may be obtained upon request to the Executive Secretary, The Geological Society of America, 231 East 46th Street, New York, N. Y. 10017, as long as they are available.