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The dark grey rock of the peninsula originated from a volcano some 300 million years ago. Lava (liquid rock) flowed out of cracks in the earth from a depth of 40 - 50 km and cooled into basalt, a mineral. The bands of red that layer the rocks are not volcanic but mud from an ancient sea floor that was under water when the volcano erupted. The lava flowed over and under the cold, red mud and solidified it into siltstone. Glaciers (layers of ice up to 1.5 km thick) then moved across these rocks in the last ice age and left scratches across the rock from the debris embedded in the moving ice. When the glacier melted about 13,000 years ago, it left behind in a high bank the rocks, mud and soil (till) it had carried. Mounds of till are found along the park’s shoreline banks. This mound wall known as a berm blocked the St. John River from flowing out to the sea through the saltmarsh. Instead the river was forced into the narrow rocky gorge that became known as Reversing Falls.
With the tides of the Bay of Fundy coming in and out twice daily to heights of 8.5 meters (28 ft.), there is intense wave action on the ancient volcanic rocks and on the plants and organisms living along the shoreline of Irving Nature Park. Many marine creatures like periwinkles live in the pools of tidal water left in rock cavities. These are some of the toughest living organisms in the park! They are submerged in frigid bay water (approximately 5°C) for six hours at high tide and then are exposed to air for six hours at low tide when the air temperature may be as hot as 30°C in summer or -30°C in winter. Waves can be wild on this shoreline. During a typical storm the wave action on seaweed fastened to the rocks can be compared to a 1,440 kph (900 mph) wind on an oak tree.
Because of the Bay of Fundy's great tide differentials, visitors can walk on the ocean floor at low tide and examine creatures living in the tidal pools. Some of the marine animals most frequently found include periwinkles, crabs, mussels and a bug-like creature, the side-swimmer. Sometimes you can see a sea anemone in a pool, its stinging tentacles waving in the water, catching tiny marine animals called plankton.
The dark green seaweed attached to the rocky shore has adapted to this large tidal variation and the rough wave action. It attaches very strong “hold fasts” to the rocks to keep from being carried out to sea. Air sacs along the stems of the seaweed allow the plant to float at high tide to capture sunlight for photosynthesis. The seaweed provides a hiding place for some of the shore’s most tiny marine creatures to hide from predators.