Earthcaches are designed to be educational and teach an earth science lesson in a fun way.
This earthcache will introduce you to the Rockwall Wall of Rockwall, TX. This town about 20 miles northeast of Dallas was established April 17, 1854 and named after the rock walls found in the area. These walls were accidentally discovered in 1852 when settlers were in the process of digging a well and hit a stone formation. Many believed prehistoric people constructed this ancient wall. Most of the walls are underground.
In 1874 after examining the rocks, geologist Richard Burleson concluded they were a natural formation. The U.S. Geologic Survey published an article in Science in 1909 and “determined that it was made of sand dykes that intruded in Cretaceous rock…” In other words, the stones are made up of sand-sized particles that cemented together and over time, dried and hardened. This material can often break as it condenses, which forms various patterns. The wall is said to be somewhere around 85 million years old.
The dikes are of various sizes, varying from an inch in thickness to eighteen inches. They stand almost vertically and have been observed downward 50 feet, always imbedded in the lime muds. They are composed of fine-grained quartz sands, cemented by calcium carbonate.
A more recent analysis by forensic geologists in 2013 identified unique features of the Rockwall wall. “ What looked like mortar between the stone blocks was actually sandy-clay from the surrounding rock that had squeezed between blocks.” The sandstone fractured in a way that appears to be in the shape of bricks-- stacked, long and narrow, forming what gives the impression of a “rock wall.” The curve to the upper surface of one block exactly fits the curve on the under surface of the next block above. Analysis of the magnetic orientation of the rocks from the time of their formation, showed a common direction which indicates the walls are natural.
The area of the walls is 20 square miles. About 3.5 miles wide and 5.6 miles long. None can be seen today above ground. The walls have been destroyed or covered as the City of Rockwall has grown. A section of the rocks is now on display outside the Rockwall County Historic Foundation’s museum. It has been reconstructed using excavated stones from the original formation.
Logging requirement, send me an email with your answers:
- How were these rock walls formed?
- What is unique about the Rockwall Wall?
- Describe the look and feel of the rock wall – color, texture, shape
While at this cache, be sure to visit the adjacent county historical museum for more information on the Rockwalls and early life in this area.
We will notify you when the CORRECT answers have been received; at that time you may log. Thanks