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List R - Rock units

List R  Rock units - alphabetical list

General notes
These thesaurus lists, lists A-R, are used by GeoRef indexers for selecting index terms and by searchers for additional information not necessarily found in individual term records in the body of the Thesaurus. In most cases, an hierarchical list is given. In some cases, an alphabetical or other list is provided.

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.

Rock units
This alphabetical list of rock units includes valid terms used for various rock units, including formations and some complexes, intrusions, etc. (Some similarly named units such as complexes or intrusions may be used as geographic terms). The list shows which rock units are autoposted with their broader age or stratigraphic terms, see List E-1 and which either lack autoposting, or lack some part of it. Additional age terms are added by the indexer where available.

Searching
To search for rock units, the most effective method is to either view the Basic Index beginning with the first part of the name and gather variations on the name or to search using stemming or truncation. See searching, basic search on page x of the GeoRef Thesaurus, 11th edition Introduction.

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. 

Indexing
The form of the term used in indexing should conform to the form found on the list. If no form of the rock unit exists in this list, index using the form provided by the author. In addition, index the appropriate age term where possible. Ages are autoposted to those rock units commonly used for correlation. Note that some formations extend over several ages or may be of indeterminate age. In these instances, the age must be added manually if known.

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