The following questions need to be answered for this earthcache:
QUESTION 1. Is this an INTRUSIVE or EXTRUSIVE igneous rock?
QUESTION 2. What size are the crystals in this rock and why are they that size?
QUESTION 3. The Northern side of the rock looks much different than the other sides due to weathering. Please describe what you see on this side of the rock.
OPTIONAL PHOTO: Posting a photo that readily indicates that you (and anyone else logging the find) are at the location.
MEADE TAKES COMMAND:
On June 28, 1863, Union General George Gordon Meade was awakened in his tent just outside of Frederick by a courier from President Lincoln with orders for him to take command of the Army of the Potomac. It was just up the hill from the posted coords on the grounds of Frederick’s Prospect Hall mansion where Meade replaced General Joseph “Fighting Joe” Hooker as commander of the Army of the Potomac. Meade then proceeded to lead his Army into Pennsylvania, engaged Confederate General Robert E. Lee, and beat him a decisive victory in three days.
In 1930, a diabase block taken from near the famous Devil’s Den at Gettysburg National Battlefield was placed at this location in Frederick to commemorate that change of command.
About 200 million years before General Meade engaged in the Battle of Gettysburg, a war between tectonic plates was going on underground. The shifting of these plates created a basin known as the Gettysburg Formation, a basin made up of sandstones, siltstones, and shales. Two 50-foot dikes and a mile wide, 2000 foot deep sill of diabase was thrust into this basin and created jagged topography of Devil’s Den.
Did you know that Lava and Magma make two different rocks? This is the result of how each one cools. You see, the longer it takes for lava/magma to cool, the larger the crystals grow in the rock. Lava on the Earth’s surface exposed to the atmosphere cools quickly and makes EXTRUSIVE ROCKS. Magma that stays insulated deep underground and cools slowly inside sills create INTRUSIVE ROCKS.
Diabase is like granite, and is an igneous intrusive rock that formed from cooling magma over a long period of time underground. Because it cooled slowly you can easilt see teh salt and peppering of the minerals pyroxene and feldspar.
Diabase stone taken from Devils Den is dense and very resistant to weathering. Weathering is the wearing down or breaking of rocks while they are in place. Weathering can be biological, chemical or physical:
Biological Weathering is caused by the movements of plants and animals.
Chemical Weathering describes the process of chemicals in rainwater making changes to the minerals in a rock.
Mechanical or Physical Weathering occurs when physical processes affect the rock, such as changes in temperature or when the rock is exposed to the effects of wind, rain and waves. Granite is especially good at holding heat and can reach temperatures more than 40 degrees higher than the surrounding air. Stones expand when they gets hot, and contract as they get cool. If the temperature changes rapidly in either way, cracking can occur.
Permission for this earthcache placement was given by Visit Frederick - Maryland Visitors Center.
This earthcache is also approved by Awesnap, which is a big deal!