Catoctin Formation

01_catoctin_columnar_metabasalt_2 Columnar metabasalt from Catoctin Formation. Columns are formed perpendicular to the cooling surface. Indian Run road cut on Skyline Drive.

02_catoctin_columnar _metabasalt_2 Columnar metabasalt from Catoctin Formation with lichen. Indian Run road cut on Skyline Drive.

03_catoctin_columnarmetabasalt_15 Heavily weathered and tilted columnar metabasalt. Bearfence mountain.

04_catcoctin_columnarmetabasalt_15 Heavily weathered and tilted columnar metabasalt. Bearfence mountain.

Severely weathered and eroded columns of metabasalt covered by lichen and fern and further fragmented by hardwood trees. Trail above Little Stony Man Park area.

05_catoctin_basaltcolumnsweathered_9 Severely weathered and eroded columns of metabasalt covered by lichen and fern and further fragmented by hardwood trees. Trail above Little Stony Man Park area.

Green metabasalt in the road cut near Loft Mountain Overlook. The green color of metabasalt is due to marked heating and pressure during metamorphism. Hot fluid carries calcium from one portion of metabasalt to another to form epidote pods. Magnesium and sodium are transported from the epidote pod to surrounding basalt.

06_catoctin_greenmetabasalt_17 Green metabasalt in the road cut near Loft Mountain Overlook. The green color of metabasalt is due to marked heating and pressure during metamorphism. Hot fluid carries calcium from one portion of metabasalt to another to form epidote pods. Magnesium and sodium are transported from the epidote pod to surrounding basalt.

Vesicles in metabasalt where hot gas was trapped while the lava cooled. Road cut at Signal Knob overlook on Skyline Drive.

07_catoctin_metabasalt_1 Vesicles in metabasalt where hot gas was trapped while the lava cooled. Road cut at Signal Knob overlook on Skyline Drive.

Wet amygdaloidal basalt in the stream area immediately above the main falls in Dark Hallow Falls area. Amygdules are gas pockets that fill with minerals precipitated by hot water: quartz, feldspar, epidote and/or hematite. The metamorphically harden to be more resistant to erosion than metabasalt and stick up from eroded surfaces.

08_catoctin_metabasalt_amygdules_13 Wet amygdaloidal basalt in the stream area immediately above the main falls in Dark Hallow Falls area. Amygdules are gas pockets that fill with minerals precipitated by hot water: quartz, feldspar, epidote and/or hematite. The metamorphically harden to be more resistant to erosion than metabasalt and stick up from eroded surfaces. Dark Hallow Falls. Water runs over Catoctin Formation terraces of metabasalt.

09_catoctin_metabasalt_darkhallowfalls_13 Dark Hallow Falls. Water runs over Catoctin Formation terraces of metabasalt.

10_catoctin_brecca_9 Formations of metabasaltic breccia on Little Stony Man Mountain at the top of the trail from Little Stony Man Park.

11_catoctin_brecca_9 Detail of metabasaltic breccia on Little Stony Man Mountain including bonded rocks, tuff and metabasalt.

Layer of eroded sandstone between layers of metabasalt. Catactin lava flows were periodic with 100’s to thousands of years for deposition of sedimentary interbeds such of this composed of sandstone. It originated from deposition of silica-rich sediment from streams, rivers and lakes. Road cut at Signal Knob overlook on Skyline Drive.

12_catoctin_sandstone_1 Layer of eroded sandstone between layers of metabasalt. Catactin lava flows were periodic with 100’s to thousands of years for deposition of sedimentary interbeds such of this composed of sandstone. It originated from deposition of silica-rich sediment from streams, rivers and lakes. Road cut at Signal Knob overlook on Skyline Drive.

13_catoctin_sandstoneconglom_1 Detail of sandstone conglomerate from road cut at Signal Knob overlook.