Origin of the American Qantitative Igneous Rock Classification: Part 2

After the tragic premature death of George Huntington Williams in 1894, the attempt by four young American petrographers to collaborate on construction of a quantitative classification of igneous rocks fell apart. The three survivors of the original quartet, C. Whitman Cross, Joseph P. Iddings, and Louis V. Pirsson, kept up their close friendship but produced their important petrological papers, including some contributions relating to classification, independently. In time, Henry Stephens Washington befriended the three.

Discussions about igneous rock classification at the VII International Geological Congress (St Petersburg, 1897); establishment of the International Committee on Rock Nomenclature; efforts to develop an international classification; and renewed discussion at the VIII International Geological Congress (Paris, 1900) re-ignited Iddings' passion to develop a cooperative American scheme. Beginning with preliminary conferences at Iddings' instigation at annual meetings of the Geological Society of America in Washington, DC (1899), and Albany, NY (1900), Cross, Iddings, Pirsson, and Washington renewed the effort to produce a new classification to be based on chemico-mineralogical principles.

In the first three months of 1901, Iddings and Washington offered proposals on the number and identity of major factors, namely chemically-based mineral groups, on which to base initial subdivision into major rock groups. They also generated ideas for diagrams on which to represent major rock groups in terms of the major factors, and they took tentative steps toward a new rock nomenclature. Remaining somewhat in the background, Cross and Pirsson cheered on their friends and offered an occasional response to the proposals.