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The controversial concepts of Edward Oscar Ulrich (1857–1944) dominated American stratigraphy during the first decades of this century. His U.S.G.S. mapping experience and extensive knowledge of the paleontology and stratigraphy of North America culminated in his masterwork: Revision of the Paleozoic Systems (1911) and several late papers (1916, 1920, 1924). The revision, which served as a guide to a generation of geologists, also contains Ulrich’s philosophy of correlation.

Application of his geological concepts to American stratigraphie successions led Ulrich to propose radical changes in existing classifications and correlations. Among his more controversial proposals were the creation of two new lower Paleozoic time stratigraphie units of systemic rank, the Ozarkian and the Canadian; a theory of oscillating troughs and barriers to explain the occurrence of the shelly carbonate and graptolitic shale facies in adjacent strike belts in the Appalachians; and the revision of the Croixan Series of the Upper Mississippi Valley. Each of these proposals was incorporated in various textbooks and correlation charts of the period.

However, as detailed stratigraphie studies in the Ozarks, the Upper Mississippi Valley, and in the Appalachians were completed, it was found that Ulrich’s concept of correlation was untenable and it was gradually replaced by one stressing facies relations. But, because of his authority, his disputative nature, and the tenacity with which he held his views, the development of American stratigraphy had been hampered.

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