Don’t be Erratic, Get Morphed
This Earthcache is located in Tomball, Texas. Since it is an Earthcache, there is no physical container to find. To earn a smiley for the cache, email or message the cache owner your answers to the questions BEFORE you log a find.
Erratic
An erratic is a glacier-transported rock that differs from the local bedrock or topography. Erratics may be embedded in the landscape or rest on the surface. They can range in size from small pebbles to huge boulders weighing thousands of tons. These rocks or boulders can move anywhere from less than 520 feet to over 500 miles. The composition of an erratic indicates the direction of the glacier and its origins.
Erratics, first theorized and explained by the Swiss-American naturalist and geologist Louis Agassiz in 1840, played a crucial role in the initial recognition of the last ice age.
Meet the Flintstones
Approximately a million years ago, the Tomball area, located in Harris County, Texas, was completely submerged under an ancient sea. Fast forward to 20,000 years ago, and North America was in the middle of the Ice Age (as seen above). While we are not in Minnesota or Wisconsin and don’t see ‘natural’ erratics here, our bedrock was still formed.
Bedrock
No, we are not going back in time to meet Fred, Wilma, Pebbles, or Bam-Bam in Bedrock. However, we can learn more about the fictional town they lived in, Bedrock. Bedrock is the hard, solid rock beneath the surface materials here in Tomball. It is a consolidated rock, meaning it is solid and tightly bound. Bedrock can be hundreds of feet below the Earth's surface. Over time, loose soils were deposited on the bedrock, such as when the glaciers melted and sand, silt, and mud were deposited along the Texas Gulf Coast.
Fluvial Deposits
As the glaciers retreated and the water flowed toward the Gulf of America, Texas rivers such as the Brazos, Trinity, and San Jacinto carried and deposited sediment through the fluvial process over the past 20,000 years. These sediments, including sand, silt, and mud, formed the foundation, the Bedrock of the Texas Gulf Coast.
- Sandstone: Sandstone is a sedimentary rock made of grains of sand (defined as 1/16 mm to 2 mm-sized particles) that are naturally cemented together.
- Siltstone: Siltstone is a sedimentary rock primarily composed of silt-sized particles, which are finer than sand but coarser than clay.
- Mudstone: Mudstone is a fine-grained sedimentary rock composed primarily of clay and silt-sized particles.
Geo-Morphology
The three distinct rock formations of the Texas Coast's bedrock have undergone changes or evolution. In geology, morphology examines the form and structure of Earth’s surface features, including landforms like mountains, valleys, and coastlines, as well as the processes that create and modify them. Geologists have studied the morphology, or changes, of the Texas bedrock over time. This investigation can be classified as sedimentary morphology.
The Task
Your task for this Earthcache is to observe and speculate about a piece of our Texas Coastal Bedrock.
After reading the information above and observing the object at GZ, please answer the following questions:
- Look at the front of the boulder and based on the reading, which rock do you believe is in front of you? Describe its texture and color.
- Go slightly north of GZ and observe the end of the boulder. How is the end different than the front? Describe what you observe. What rock do you think is seen in the layers?
- Based on your observation, what type of rock do you think the boulder is primarily composed of: Sandstone, Siltstone, Mudstone, or Limestone? Why?
- Post a picture with the nearby business in the background.
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- DO NOT POST PICTURES of the BOULDER
Confirm your findings by answering these questions and sending
Your answers via the message center.
**Do not post answers in your log**
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References:
North Dakota Geological Survey. 2007. Glacial Erratics. North Dakota Geological Survey. https://www.dmr.nd.gov/ndgs/ndnotes/Erratics/Glacial%20erratics.asp
Paleontological Research Institution. 2021. Rocks of the Coastal Plain. Earth@Home. https://earthathome.org/hoe/se/rocks-cp/#:~:text=As%20the%20Atlantic%20Ocean%20and,out%20onto%20the%20continental%20shelf.
Perttula, Timothy. 2025. Exploring Texas Prehistory: A Journey Through 13,500 Years. Texas State Historical Association. https://www.tshaonline.org/handbook/entries/prehistory