A conglomerate Rock is a sedimentary rock that contains many rounded clasts which are greater than 2 millimeters in diameter. (A clast is a rounded rock fragment resulting from the break down of a larger rock). These clasts can be sedimentary, metamorphic or igneous rock fragments, but the overall rock structure is sedimentary. The material that holds all of the particles together is often hardened sand or mud.
Conglomerate rocks can be formed in several ways, but most of them have common features. The rounded shape of the clasts reveals the they were tumbled for some distance by running water or moving waves or even glaciers. Conglomerates often begin when a sediment consisting mainly of pebble and cobble size clasts is being deposited. The finer size sand and clay which fills in the spaces between the larger clasts is often deposited later on top of the large clasts then sifts down between them to form the matrix (or chemical cement)that binds the sediment into a rock.
Conglomerates are often classified according to the dominate clast size comprising them. Below is a chart used for this type of classification.
Granule conglomerate 2-4 mm
Pebble conglomerate 4-64 mm
Cobble conglomerate 64-256 mm
Boulder conglomerate >256 mm
During the Paleozoic era this area was covered by a shallow saltwater sea. As time passed, it is likely that many of the rocks in Allegheny State Park eroded here from the nearby Catskill Mountains. Over time frost wedging and gravity erosion shaped this rock and pushed it to its present position. Looking at this rock, you can easily see a narrow row of clasts about three feet from the top of the rock, notice the different colors of clasts in this layer. While conglomerate rocks are interesting to observe, their makeup is easily degraded when they are exposed to the elements; hopefully this one is here for many years to come for all to enjoy.
LOGGING REQUIREMENTS: Send me the answers to the questions below.
1. How would you classify this rock by clast size as described above?
2. Tell me three colors of clasts found in this conglomerate.
3. Do you think this conglomerate rock was formed by water and erosion or glacial movement?
4. What is the approximate overall height of the rock?
5. How many exposed sides are there on this rock?
As per Earthcache rules, I must delete your log if I don't receive your answers within 5 days of your visit. Thank you for visiting my Earthcache.
This Earthcache is developed with permission of the Office of Parks - Recreation and Historic Preservation at Allegany State Park and has been given permit number ALL469.
