Geologic units in Clay county, Alabama

Additional scientific data in this geographic area

Mad Indian Group (Precambrian to Paleozoic) at surface, covers 19 % of this area

Fine-grained feldspathic biotite gneiss; medium to coarse-grained muscovite-biotite-garnet schist; locally kyanite and sillimanite. Many of the schists have been retrograded to chlorite-garnet-quartz-sericite schist. Both mi and migr extensively cut by feldspathic dikes and pegmatites.

Talladega Group; Lay Dam Formation (Silurian?-Devonian) at surface, covers 18 % of this area

Interbedded dark-green phyllite, medium-gray to light-brown and black metasiltstone, dark-green feldspathic metagraywacke, and light-gray and dark-gray medium to coarse-grained arkosic quartzite and metaconglomerate; graphitic phyllite common in upper part. In Cleburne and Calhoun Counties, rocks mapped as the Lay Dam include the Abel Gap Formation of Bearce (1973) and consist of interbedded greenish-gray metasiltstone and quartzite, black phyllitic metasiltstone, medium-gray to greenish-gray arkosic quartzite, and dark-gray pyritic quartzite. In Clay Chounty the upper part of the Lay Dam includes black graphitic sericite phyllite and slate reportedly containing plant fossils (Erin Slate Member).

Wedowee Group; Wedowee Group undifferentiated (Precambrian to Paleozoic) at surface, covers 11 % of this area

Wedowee Group undifferentiated includes the Cragford Phyllite and Cutnose Gneiss. Cragford Phyllite -- interbedded fine-grained graphite-chlorite-sericite schist and phyllite, garnet-sericite schist and phyllite, graphite-quartz-sericite phyllite, locally feldspathic biotite gneiss, calc-silicate rock, and quartzite. Cutnose Gneiss -- cyclically interbedded fine-grained quartz-biotite feldspathic gneiss, graphite-chlorite-sericite schist, locally thin interbeds of graphite-quartz-sericite phyllite, and quartzite. Rocks in the area northeast of Clanton in Chilton and Coosa Counties that are here assigned to the Wedowee Group also have been interpreted as part of the Higgins Ferry Group.

Wedowee Group; Hackneyville Schist (Precambrian to Paleozoic) at surface, covers 10 % of this area

Medium to coarse-grained quartz-plagioclase +/- almandine +/- kyanite +/- biotite-muscovite schist, graphite-muscovite-quartz schist, and quartzite containing biotite. Large porphyroblasts of muscovite, andalusite and/or chiastrolite common. Rocks in the areas between Goodwater in Coosa County and Millerville in Clay County that are here assigned to the Hackneyville Schist also have been interpreted as part of the Higgins Ferry Group.

Talladega Group; Jemison Chert and Chulafinnee Schist undifferentiated (Silurian?-Devonian) at surface, covers 7 % of this area

Grayish-white to yellowish-orange massive, thick-bedded, fine-grained, locally argillaceous, locally fossiliferous metachert and light to dark-greenish-gray fine to medium-grained fissile quartz-sericite-chlorite phyllite and schist which locally includes thin chlorite phyllite and quartzose phyllite beds.

Poe Bridge Mountain Group (Precambrian to Paleozoic) at surface, covers 5 % of this area

Coarse to fine-grained feldspathic graphite schist, +/- staurolite +/- kyanite +/- sillimanite-muscovite-biotite schist, and garnet-biotite-muscovite schist, and gneiss; locally common pegmatites. Rocks in the area of Turkey Heaven Mountain in Cleburne and Randolph Counties that are here assigned to the Poe Bridge Mountain Group also have been interpreted as part of the Wedowee Group.

Ketchepedrakee Amphibolite (Precambrian to Paleozoic) at surface, covers 5 % of this area

Dark-green to black fine to coarse-grained, layered to massive amphibolite mixed with zones of chlorite actinolite schist, includes all amphibolite associated with the Poe Bridge Mountain Group.

Poe Bridge Mountain Group; Roscoelite-graphite quartz schist and graphitic quartzite (Precambrian to Paleozoic) at surface, covers 5 % of this area

Rocks in the area of Turkey Heaven Mountain in Cleburne and Randolph Counties that are here assigned to the Poe Bridge Mountain Group also have been interpreted as part of the Wedowee Group.

Bluff Springs Granite (Precambrian to Paleozoic) at surface, covers 5 % of this area

Leucocratic quartz diorite (tonalite) to quartz monzonite or trondhjemite, locally foliated.

Hillabee Greenstone (Paleozoic) at surface, covers 4 % of this area

Pale-green to light-olive-brown massive, fine-grained greenstone interbedded locally with well-foliated mafic phyllite.

Mad Indian Group; Irregular zones of sericite-quartz schist (Precambrian to Paleozoic) at surface, covers 2 % of this area

Irregular zones of sericite-quartz schist (+/- garnet) containing finely disseminated graphite, possibly infolded Wedowee Group equivalents. Both mi and migr extensively cut by feldspathic dikes and pegmatites.

Talladega Group; Cheaha Quartzite Member of Lay Dam Formation (Silurian?-Devonian) at surface, covers 2 % of this area

White to light-gray medium to coarse-grained arkosic quartzite and metaconglomerate.

Poe Bridge Mountain Group; Garnet quartzite (garnetite) and garnitiferous altered mafic rock (Precambrian to Paleozoic) at surface, covers 2 % of this area

Rocks in the area of Turkey Heaven Mountain in Cleburne and Randolph Counties that are here assigned to the Poe Bridge Mountain Group also have been interpreted as part of the Wedowee Group.

Elkahatchee Quartz Diorite Gneiss (Precambrian to Paleozoic) at surface, covers 1 % of this area

Mesocratic to melanocratic, fine to coarse-grained, massive to strongly foliated, locally sheared quartz diorite gneiss.

Wedowee Group; Cornhouse Schist (Precambrian to Paleozoic) at surface, covers 1 % of this area

Medium to coarse-grained multiply foliated +/- plagioclase +/- garnet-biotite-muscovite-quartz schist interlayed with chlorite-biotite-garnet schist, typically mylonitic.

Hillabee Greenstone, unnamed dacite unit (Paleozoic) at surface, covers 0.7 % of this area

Unnamed unit comprised of masses of well-foliated quartz dacite.

Higgins Ferry Group (Precambrian to Paleozoic) at surface, covers 0.5 % of this area

Thinly layered coarse to fine-grained biotite-feldspar-quartz gneiss, sericite-feldspar-muscovite schist, +/- biotite +/- garnet-muscovite schist, and biotite-garnet feldspathic gneiss; locally common pegmatites.

Hatchet Creek Group; Pinchoulee Gneiss (Precambrian to Paleozoic) at surface, covers 0.3 % of this area

Medium to fine-grained migmatitic, locally garnetiferous biotite-feldspar gneiss, commonly saturated with granitic pods.

Almond Trondhjemite (Precambrian to Paleozoic) at surface, covers 0.3 % of this area

Leucocratic, fine to medium-grained, locally foliated trondhjemite containing abundant muscovite and locally biotite and epidote.

Beaverdam Amphibolite (Precambrian to Paleozoic) at surface, covers 0.3 % of this area

Dark-green to dark-gray hornblende amphibolite, extensively sheared and folded, and locally retrograded to actinolite-tremolite-chlorite schist. Includes all amphibolite associated with the Wedowee Group.

Higgins Ferry Group; Roscoelite-graphite-quartz schist and graphitic quartzite (Precambrian to Paleozoic) at surface, covers 0.2 % of this area

Higgins Ferry Group; Roscoelite-graphite-quartz schist and graphitic quartzite

Talladega Group; Butting Ram Sandstone (Silurian?-Devonian) at surface, covers 0.1 % of this area

White to light-bluish-gray medium to coarse-grained, locally conglomeratic thick-bedded quartzose sandstone. Possible Devonian fossils.

Ultramafic rock (Precambrian to Paleozoic) at surface, covers 0.1 % of this area

Ultramafic pods and sheets, principally enstatite-hypersthene pyroxenite with hornblende and actinolite alteration assemblages.

Mitchell Dam Amphibolite (Precambrian to Paleozoic) at surface, covers 0.1 % of this area

Dark-green to black fine to coarse-grained, thin-layered to massive hornblende-actinolite amphibolite; includes all amphibolite associated with the Higgins Ferry and Hatchet Creek Groups.

Rockford Granite (Precambrian to Paleozoic) at surface, covers < 0.1 % of this area

Leucocratic granite, granodiorite, and trondhjemite; locally well foliated, numerous pegmatites. Includes unnamed granitoids in Chilton County.