Geologic Maps A Practical Guide to Preparation and Interpretation by Edgar W. Spencer (z-lib.org)

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MAP ABBREVIATIONS The United States Geological Survey has established standard symbols for use on the maps it publishes. These are used on most other maps also. The standard abbreviations for formations consist of a capital letter to indicate the period in which the unit was formed, followed by one or more lowercase letters to indicate the name of the formation (i.e., Ob is the symbol for the Beekmantown Formation of Ordovician age). Standard letters for periods are as follows. Era Period Symbol…