To claim this earth cache please email the answers to the following question to the cache owner.
1.From your observations which category of rocks and minerals are present?:
- Dolstone
- Limestone
- Sandstone
- Chert
2. Estimate the height of the rock.
3. What direction is the grain of the rock, vertical, slanted, horizontal to the river?
Pictures are welcome.
This feature can be found in the Ridge and Valley Province of Pennsylvania.
These rocks are of the Gatesburg Formation of the Cambrian age. The Cambrian is the first geological period of the Paleozoic Era, lasting from 541 to 485.4 million years ago. The Cambrian was unique that it had large deposits of sedimentary materials called lagerstätte, holding many well preserved fossils. Lagerstätte a German origin, Lager for 'storage' and Stätte for 'place'. Up until this period living organisms were for the most part small unicellular and simple. Multicllular life forms became more common in the few million years prior to the Cambrian age but it was this era that mineralized and created fossils of these organisms. Of both soft tissue as well as the harder shell. These life forms were more common in the seas as the land was mostly rock.
The Gatesburg Formation found in Bedford, Blair, Centre, Clinton, and Huntingdon Counties. It consists several type of sedimentary rock.
Dolestone (dolomite) is the primary type. Dolostone is mostly light gray in color. Mohs hardness is 3.5-4. Its crystals are usually small- to medium-sized, and freshly broken surfaces may glitter in sunlight.
Limestone is the secondary and made mostly of calcite. Limestone is mostly light to dark gray in color. Hardness 3. A fine grain can be mud-sized, so that the rock looks dull, or the grain can be sand-sized or larger bits of broken shell or other limey material.
Others include sandstone and chert.
Sandstone has a hardness of 6-7 on the Mohs scale. It has a dull appearance, has a grainy texture, and is porous. Can be found in many colors. Black, gray, brown, red, pink, and purple.
Chert is a hard, dark, opaque sedimentary rock which is composed of silica fine-grained texture. Colors vary from black, gray, brown, white, and red. Appearance is usually glassy.
There are several ways to observe this formation. The easiest would be to follow the Lower Trail a converted Pennsylvania Railroad bed that follows the river on the opposite side of the rock. Another possibility would be to float the river in a canoe or kayak.
reference: Wikipedia, gsa.gov