This earthcache is located at the beginning of our downstream trail tour, and marks the location of a 530 million year old beach. While it no longer looks like a cobblestone beach, you can still see the ancient cobbles cemented together in a new rock called a conglomerate (known locally as our chocolate chip cookie rock). These cobbles are made up of numerous types of igneous rocks, including granite and rhyolite as well as quartz veins, which all eroded from the volcanic cliffs that were present in this area 600 million years ago. As the beach rocks subsided below sea level, finer-grained sediments were able to fill in the gaps between them; eventually, at greater depths, these sediments formed into solid rock.
You may also notice that the rock in this area is tilted downstream. This tilt was caused by the tectonic plate collision around 400 million years ago that began the building of the Appalachian mountains. This collision affected the whole island of Newfoundland, and its effects can be seen in bedrock across the province.
As you continue further down the trail, you proceed from the ancient beach into what was once a shallow sea bed. One of the first rock types you will encounter is limestone, a rock made of carbonate minerals precipitated onto the seafloor. You will also see red shale: the distinctive colour of the rock tells us that it was originally formed in quiet shallow water, with sufficient oxygen to oxidize iron into a brownish-red rust.
Continue your journey further downstream to reach the ancient ocean floor, represented by black and grey shales. The shale present in this area was once the mud on an ocean floor. This mud has been compacted by the weight of the ocean as well as overlying sediment layers, forming the shales we see today. This is also the location of our world-renowned trilobite fossils. Trilobites were ancient arthropods who dominated the ocean floor 500 million years ago. These creatures ranged in size from less than a centimeter to approximately 90 cm long; the trilobites here at Manuels River rarely exceed 30 cm in length. While the rocks on Manuels River are now protected by provincial legislation, making it illegal to remove fossils or other rocks from this area, it is still fun to pick through the loose shale to see if you can find any of these amazing fossils.
To log this earthcache please send the answers to the following email: education@manuelsriver.com
1. Estimate the degree that the tilted conglomerate is on.
2. What direction does the river flow at this point.
3. Why would we sometimes refer to the conglomerate as the "chocolate chip cookie rock"?