This is an Earthcache – as such, there is no physical cache. Instead after examining the conglomerate rock at the posted coordinates you will answer 4 questions and message me the answers. Leesylvania State Park is open daily from sunrise to sunset. For more information on entrance fees, park rules, hours of operation, or to learn the history of the park please visit this LINK to go the the Leesylvania State Park webpage.
con·glom·er·ate: a number of different things or parts that are put or grouped together to form a whole but remain distinct entities.
Just like this grouping of different but interesting rocks displayed in front of the Visitor Center is a conglomerate. There is a petrified tree stump, a large chunk of freestone, a large rounded quartz stone, a rock embedded with dinosaur tracks, and the star of this Earthcache is something that looks like someone rolled up a bunch of small stones in in a blob of clay.
This boulder is a type of clastic sedimentary rock called a conglomerate. Conglomerates are made up of larger pebbles than other sedimentary rocks and a smooth cementing mineral. Though conglomerate rocks come in many different colors and styles, they all are made from pieces of older rocks and minerals. Conglomerate rocks are formed through four steps:
1. Weathering: The Earth’s surface goes through a physical and chemical weathering processes that causes rocks to break down into smaller pieces. Physical weathering includes gravity, abrasion by wind or water, freezing of water causing fractures, and even the roots of plants forming cracks in the rocks as they grow. Chemical weathering includes dissolving of rocks and minerals.
2. Transportation: The particles from weathered rocks move downhill with the aid of gravity, wind and water energy. Wind and flowing water can carry particles of eroding rocks. High energy water can move large boulders and low energy, while slow moving streams can only move very fine material such as sand and silt. We can tell the type and energy of transportation by examining the shape and size of the bits of weathered rock within a conglomerate.
3. Deposition: Finally sediments are deposited, or released, when there isn’t enough energy. When the energy transporting the material loses the strength to carry these particles they drop out in the process of deposition.
4. Compaction & Lithification: As more and more sediments accumulate (sometimes as great as 10 km), the added pressure causes compaction of the buried sediment particles, reducing the space between the particles. With burial the temperature and pressure increase. Water carrying dissolved chemicals can produce changes in the sediment. This cements the sediment together creating sedimentary rocks.
When a conglomerate has very angular and sharp pieces of rock instead of rounded clast it is called breccia (see below).
REFERENCES:
1. Conglomerate, King, Hobart, geology.com
2. Conglomerate, flexiblelearning.auckland.ac.nz
LOGGING REQUIREMENTS:
To log this Earthcache: Read the geology lesson above. Answer all four questions posted below. Answers can be sent via e-mail or messenger contacts on my Geocaching profile. Do not post the answers to the questions in your logs.
QUESTION 1. Conglomerate rocks are formed through what four steps?
QUESTION 2. Do you think it was formed in a low or high-energy environment?
QUESTION 3. A conglomerate is made up of a clast of smaller stones. How would you classify this rock by clast size as described in the chart below?
| CONGLOMERATE CLAST SIZE CHART |
| GRANULE CONGLOMERATE |
2 mm to 4 mm (.08 inches to .15 inches)) |
| PEBBLE CONGLOMERATE |
4–64 mm (.15 inches to 2.5 inches)) |
| COBBLE CONGLOMERATE |
64–256 mm (2.5 inches to 10 inches) |
| BOULDER CONGLOMERATE |
>256 mm (10 inches or more) |
QUESTION 4. Do you think that this specimen is breccia?
OPTIONAL PHOTO. Posting a photo with your favorite rock in this outdoor display readily indicates that you (and anyone else logging the find) are at the location.
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