The first chapters in the story of PEI are written in sandstone, and they tell us about the environment and the plants and animals that lived here some 300 million years ago. You might think all our bedrock is sandstone, but there’s one place on the Island where a different type exists: Iron Rock in Malpeque Bay.
Iron Rock is unlike any other formation on PEI because it is igneous, not sedimentary. Igneous rocks form from the cooling of hot, liquid rock. You can find igneous rocks scattered around the Island, but these are ‘from away’ and were carried here by ice sheets during the last glaciation. Iron Rock is different in that it is a sill – igneous rock that forced its way between layers of sedimentary rock – and was here long before the last ice age.
I often hear Iron Rock called volcanic, but that’s not correct. Volcanic rocks are formed from volcanic eruptions and classed as ‘extrusive’. In these cases, lava cooled quickly once it hit the surface, and the rocks that resulted are fine-grained: basalt, obsidian, and pumice are examples. Iron Rock is ‘intrusive’, meaning its magma cooled underground and slowly, forming larger grains (like granite, another intrusive igneous rock). In short, all volcanic rocks are igneous, but not all igneous rocks are volcanic. (And liquid rock is called lava when it hits the surface, magma if underground).
Iron Rock is indeed rich in iron – and other minerals such as calcium and magnesium – and so is well-named. We know it’s younger than the surrounding sandstone because those sedimentary layers had to be there first for the igneous sill to force its way through. Iron Rock dates back to the early years of the Dinosaurs, about 247 million years ago, and it records a time of increased geological activity preceding the separation of the supercontinent Pangea. In the tens of millions of years that followed, the Earth’s surface was stretched thin and eventually torn apart, creating the Atlantic Ocean.
The area around Iron Rock is not only geologically important, but also ecologically and culturally significant. It includes old growth forest with provincially rare plant species; offshore islands and coastal dunes that are among the last wilderness areas on PEI; and archaeological evidence that shows a deep history of importance to and use by Mi’kmaq people.
This extraordinary combination of factors has led to an agreement to designate the greater area as Pituamkek National Park Reserve (Pituamkek is pronounced Bee-DOO-um-gek and means ‘at the long sand dune’ in the Mi’kmaq language). This cooperative effort among First Nations, Federal and Provincial Governments, and non-governmental organizations will ensure protection of this important geological, ecological, and cultural landscape for generations to come.
If you’re interested in learning more about PEI’s globally-significant rocks and fossils, join me on February 18 when Laura MacNeil will be the special guest at my monthly Zoom workshop. She’ll guide us through PEI’s geology and recent fossil discoveries that are re-writing what we know about the Permian Period. You can find all the details on my website, PEI-untamed!
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