Catoctin Formation

The Catoctin Formation is a geologic formation that expands through Virginia, Maryland, and Pennsylvania. It dates back to the Precambrian and is closely associated with the Harpers Formation, Weverton Formation, and the Loudoun Formation. The Catoctin Formation lies over a granitic basement rock and below the Chilhowee Group making it only exposed on the outer parts of the Blue Ridge. The Catoctin Formation contains metabasalt, metarhyolite, and porphyritic rocks, columnar jointing, low-dipping primary joints, amygdules, sedimentary dikes, and flow breccias. Evidence for past volcanic activity includes columnar basalts and greenstone dikes.

Stratigraphy of the Catoctin Formation is closely related to the Harpers Formation, Weverton Formation, and the Loudon Formation.

The Harpers Formation is part of the Chilhowee Group. This formation is found above the Weverton Formation and is around 2000–2750 feet in thickness. This formation contains gray phyllite and slate which can be found with banded quartz throughout the rock. It varies in thickness throughout the area and has folds such as anticlines that cause the formation to repeat on itself. Lots of cleavages can also be found throughout which causes the beading to break apart easily.

The Weverton Formation is part of the Chilhowee Group. This formation is found below the Harpers Formation and above the Loudon Formation and is around 1250 feet in thickness. This formation has lots of beds and layers of different types of rock throughout the formation. Different colors, such as gray and purple, and textures, such as vitreous and granular, of quartzite, can be found. Cross-bedded in the quartzite layers is conglomerate layers. White quartzite layers and shale beds between those layers can be found in many different layers.

The Loudon Formation is part of the Chilhowee Group. This formation is found below the Weverton formation and above the Catoctin Formation and is around 150–450 feet in thickness. This formation contains iron oxide, dark, phyllite along thin beds of arkosic quartzite and layers of conglomerate rock. Also contains layers of the matrix that contains blue and green slate as well as a conglomerate with quartz pebbles.

The Catoctin Formation found under the Chilhowee Group and above the basement rock(1.2-1.0 Ga) and is around 100–400 feet in thickness. Unconformities can be found between the Catoctin Formation and the Laudon Formation as well as between the Catoctin Formation and the basement rock. This formation has metabasalts and metarhyolite as result of metamorphism. The metabasalts can also be seen paired with amygdalar layers and quartz, calcite, and epidote. The metarhyolite is seen with breccia and purple slate. Hornblende-calcite schist and greenstone are found folded and altered in the Catoctin Formation. The Basement Rock lays under all of the other rock formations and has an unconformity between it and the Catoctin Formation. The basement rock contains granite, anorthosite, quartz monzonite, syenite, and para-gneiss.

Many different types of features can be found throughout the Catoctin Formation. These features include columnar jointing, low-dipping joints, amygdules, sedimentary dikes, flow breccias, dikes of greenstone, and purple volcanic slate.

Some columnar jointing is well preserved in the Catoctin Formation but most of it shows harsh columnar jointing. The well-preserved columnar jointing up to 20 feet tall and 1 foot in diameter. The harsh columnar jointing is shorter in height and can have a diameter of 2 to 3 feet. Most columnar jointing is parallel but some have a curved or random orientation.