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List R - Rock units
List R Rock units - alphabetical list
The notes under Searching attempt to guide the searcher in the use of the list. Searchers might also read the notes on Indexing for further clues but should be aware that these notes reflect current practice which in some cases differs from past practice. Further notes on specific terms are in the body of the Thesaurus and additional notes on searching are in the GeoRef Thesaurus, 11th edition Introduction section on searching beginning on page x. Information specific to searching and the individual list topics is included, e.g., a section including rock units begins on page xi.
Under Indexing the current indexing practice is given. These notes should be read along with the instructions under the individual terms in the body of the Thesaurus.
There is a great deal of variation in the literature. Authors may propose a new formal name with proper documentation in any formal paper. Therefore, the searcher is cautioned to use every possible variant, e.g. Smith Formation, Smith Sandstone, Smith Group, etc., even after the year GeoRef established a valid term. Indexers may index a variation for a valid term if the controlled term does not fit the form used in the paper, most commonly because of lithologic (e.g. sand versus siltstone) variations. Until a rock unit is added to the controlled vocabulary the term is entered as it appears in the document. In a few cases, the same geographic name occurs in unrelated locations, e.g. Windermere System in Canada and Windermere Group in England. In most of these cases, the ages will also differ and the unwanted age or geography may be excluded. Occasionally official changes are made in stratigraphic nomenclature. These are incorporated into the controlled vocabulary as they are identified.
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