Figure 4. Each map unit of stratified rock on the 1985 Bedrock Geologic Map of Maine carries a light gray overprint pattern from this Protolith chart, indicating the dominant protolith of the unit. The letter in parentheses for each protolith is used in the List of Formations also to identify the protolith for each map unit. A protolith is the precursor rock from which a present metamorphic rock was derived. Therefore, mineralogical and textural changes which accompany metamorphism may result in significant differences between the present lithology and the protolith listed here. Also, since most geologic units are naturally complex, readers should be aware that variations or minor rock types are not represented. The information sources listed elsewhere on the map should be consulted for lithologic descriptions of rocks in specific areas of the State.

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Last updated on March 7, 2008

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