Welcome to my Earthcache! An Earthcache is a special type of geocache where there is no container to find - instead you are looking for a unique geological feature of the area and need to answer questions, as well as posting a picture, in order to claim the find. The goal of this Earthcache is to educate visitors about Grand Iver Conglomerate, erratics and how ancient rivers caused them to travel inland.
The conglomerate erratic you are looking for is located a short distance off of the Grand Valley Trail, which can be accessed from the waypointed parking and trailhead coordinates. This is a short but fairly challenging hike with lots of tripping hazards, elevation changes, slippery sections and mud. You will want deet in the summer, boots in the wet season, and proper footware year round. This is NOT a wheelchair, stroller, child or flip-flop friendly hike.
EARTHCACHE REQUIREMENTS
As with all of my ECs, I am not looking for PhD thesis level responses, but I am hoping that you take some time to enjoy the area and learn something new. Please include a list of all cachers with your answer, if answering for more than one caching name. There is no need to send individual answers.
To claim a 'find' for this Earthcache you must answer the following questions and send your answers in a message or email to the owner using the link at the top of the page. You can log your find with a photo at GZ. Send your answers to the tasks. I will be in contact if there is a problem, no need to wait for a response as long as the required photo is included in your log.
Observational Task
At GZ, you will locate a small erratic just off the trail, in the bottom of an ancient ravine, that is now part of the Grand Valley Trail. Observe the erratic, including the clasts(what makes up the erratic), the matrix (the glue that holds all of the stones together) and what makes it diffetrent from other nearby rocks, and answer the following questions:
EarthCache Logging Tasks:
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Describe the size, texture and colour of the clasts that make up the conglomerate at the site. Are the clasts well-rounded, sub-rounded, or angular? Using the chart in the description, how would you classify these clasts?
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Describe the size, texture and colour of the matrix that makes up the conglomerate at the site. Is the matrix gritty, sandy, smooth, rough, have visible particles, resemble another common item?
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Identify at least two types of clasts you observe (e.g., quartzite, granite, limestone) and explain why these prove that this is a river conglomerate.
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In your own words explain why this deposit is found far from the current Grand River, based on your observations and the information above.
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Photo: Mandatory: Include a photograph of yourself, your GPS, a signature item, thumbs up, etc at the erratic. You do not need to show your face in the photo, but your photo must be unique to you. Each log must include their own photo.
Please send me the answers using the Geocaching Message Center or send me an email with your answers to the above questions, then go ahead and log this earthcache. You do not need to wait for my response to log. I will contact you if there are any issues with your answers. Feel free to post additional pictures as well, but please do not post your answers with your log.
Geology Lesson
What is Conglomerate?
Conglomerate is a type of sedimentary rock that is composed predominantly of rounded clasts—small to large pebbles, cobbles, and sometimes boulders—cemented together by a finer-grained matrix like sand, silt, or clay. The clasts in a conglomerate are typically larger than 2 mm in diameter but can be classified using the following chart:
Classifications of Rock Sizes, of Grain Sizes.
Their rounded shapes indicate they were transported by water or sometimes by glaciers, smoothing their edges over time.
How is Conglomerate Formed?
Conglomerates form through a multi-step natural process:
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Weathering and Erosion: Larger rocks break down into smaller pieces due to wind, rain, and freeze-thaw cycles.
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Transportation: The fragments are carried by rivers, streams, or glacial meltwaters. While traveling, the rocks knock against each other and become rounded and smoothed.
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Deposition: Eventually, the flowing water slows down—perhaps as it enters a floodplain or delta—and deposits these heavy clasts along with finer sediments.
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Lithification: Over time, layers of deposited material are buried and subjected to pressure. Natural minerals like silica, calcite, or iron oxides precipitate from groundwater and act as cement, binding the sediments into solid rock.
Composition of the Grand River Conglomerate:
In this location along the GVT, the conglomerate consists primarily of:
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Quartzite pebbles: Tough and highly resistant to erosion.
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Granite fragments: Indicating an ancient, distant source.
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Sandstone and limestone bits: More easily eroded but still present.
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Sandy matrix: Fine sand fills in gaps between the larger pebbles.
The variety and composition of these clasts suggest that the source materials were transported from multiple upstream regions including the Niagara Escarpment (linestone and dolostone) and Northern Ontario (Canadian Shield granite and gneiss). These clasts would have been transported dutring the last ice age, where the ice was almost 2km think in spots - about 10,000-12,000 years ago. These glacial deposits would have been cemented into conglomerate under immense pressure.
How Can You Tell This is River Rock?
Several key features help you recognize river conglomerate:
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Rounded clasts: The pebbles and stones embedded in the rock are smooth and rounded, not sharp or angular, showing they were shaped by rolling along a riverbed.
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Size sorting: The rocks may show a rough pattern where similar-sized clasts are grouped together—typical of sediment deposited by water.
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Mixed lithology: A variety of rock types are present, reflecting a river’s ability to gather materials from many locations.
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Color: Often, the rocks exhibit a "wet" polished look even when dry, as years of river tumbling wear away surface roughness.
How Did River Rock End Up on the Trail Far from the River?
As you walk along the Grand Valley Trail today, you may notice rounded river rocks embedded in the trail far from the current course of the Grand River, which flows hundreds of meters away. Their presence reveals a fascinating story of ancient landscapes shaped by powerful natural forces. Around 12,000 years ago, at the end of the last Ice Age, retreating glaciers dramatically reshaped the terrain of what is now southern Ontario. Immense meltwater rivers, far larger than the modern Grand River, surged across the land, carrying with them vast amounts of sediment—boulders, pebbles, sand, and silt. At that time, the Grand River, or one of its ancestral channels, flowed directly over this area, depositing thick layers of river sediment along its banks and floodplains. As the glaciers continued to retreat and the land rebounded and shifted, the river gradually migrated to its present-day course, leaving behind isolated patches of these ancient deposits. Over thousands of years, natural processes of compaction and cementation transformed the loose sediments into solid rock, forming the hardened river conglomerate now visible along the trail. In essence, the conglomerate you see today is a fossilized riverbed—a lasting memory of a time when massive volumes of glacial meltwater and dynamic river systems dominated the landscape, leaving their mark in stone.
This EarthCache has been prepared by a proud:
