|Name||Devonian - Ordovician Spruce Top Greenstone|
|Geologic age||Devonian - Ordovician|
Metamorphic > Metaigneous > Greenstone (Zeolitic (prehnite-pumpellyite))W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; Protolith V - Basaltic volcanic rocks
|Comments||The bulk of the Fredericton trough in ME is composed of three formations: the Ordovician and Silurian Pocomoonshine Lake, the Silurian Digdeguash, and the Silurian and Devonian Flume Ridge. The Flume Ridge is the most extensive of the three, extending 20 mi across strike from its contact with the Digdeguash. Underlies a large part of the Big Lake quad and almost all of the Waite 15-min quad. Most of unit consists of variably calcareous quartzofeldspathic wackes interbedded with calcareous and non-calcareous siltstones and non-calcareous slates. Appearance changes drastically from chlorite zone to higher metamorphic grades. Thickness is estimated at 20,000 ft. Flume Ridge is equivalent to the Bucksport Formation of mid-coastal ME and the Hutchins Corner Formation. Intruded by the Pocomoonshine gabbro-diorite, the Bottle Lake pluton and the Pokiok pluton. Rocks of the Fredericton trough span the Late Ordovician through at least Middle Silurian time. Flume Ridge is mapped in fig. 3 as Silurian and Devonian. (ME033). Unit description from USGS GEOLEX website (ME078). W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; GS - Greenschist facies; Protolith M - Calcareous sandstone; interbedded sandstone and impure limestone.|
Osberg, P.H., Hussey, A.M., and Boone, G.M., 1985, Bedrock geologic map of Maine: Maine Geological Survey, Dept. of Conserv., scale 1:500,000.