The
Cambrian
The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...
Chickies Formation is a mapped bedrock unit in
Pennsylvania,
New Jersey, and
Maryland. It is named for
Chickies Rock, north of
Columbia, Pennsylvania along the
Susquehanna River
The Susquehanna River (; Lenape: Siskëwahane) is a major river located in the Mid-Atlantic region of the United States, overlapping between the lower Northeast and the Upland South. At long, it is the longest river on the East Coast of the ...
.
Description
The Chickies Formation is described as a light-gray to white, hard, massive
quartzite and quartz
schist with thin interbedded dark
slate
Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock. ...
at the top. Included at the base is the Hellam Conglomerate Member. It is a rare
metamorphic rock that has
fossils
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...
; ''
Skolithos'' is found throughout the formation.
Depositional age
Relative age dating places the Chickies in the
Lower Cambrian Period, deposited between 542 and 520 million years ago (±2 million years).
[Blackmer, G.C., (2005). Preliminary Bedrock Geologic Map of a Portion of the Wilmington 30- by 60-Minute Quadrangle, Southeastern Pennsylvania. Pennsylvania Geologic Survey, Open-File Report OFBM-05-01.0.]
Economic geology
The Chickies is quarried as a building stone and for aggregate. The stone used to build the restrooms at
Valley Forge National Historical Park is Chickies quartzite.
Article title
File:Bulletin 799 Plate 8B Chickies Banded Slate.jpg, Specimen of Chickies Banded Slate. Shows older folded schistosity parallel to bedding cut by younger cleavage inclined to bedding.
File:Bulletin 799 Plate 8C Mica Schist from Upper Beds of Chickies Quartzite.jpg, Specimen of mica schist from upper beds of Chickies Quartzite. Shows stretched epigenetic tourmaline.
File:Cobble bed in Hellam conglomerate member of Chickies quartzite sgw02104.jpg, Cobble bed in Hellam Conglomerate Member
See also
* Geology of Pennsylvania
References
{{reflist
Geologic formations of New Jersey
Cambrian System of North America
Cambrian Maryland
Cambrian geology of Pennsylvania
Quartzite formations