The rocks along the Manuels River are 500-600 million years old. They are among the oldest rocks in Newfoundland, but they are not nearly as old as the Earth itself (4 500 million years). Rocks of the Manuels River are remnants of the ancient African continental plate that collided with North America 400 million years ago. Plates are large pieces of the Earth's brittle outer shell which move very slowly, driven by forces from below. Edges of plates are commonly sites of earthquakes and volcanoes. Most of the world's mountain ranges were formed by plates pushing against each other. 400 million years ago, the Appalachian Mountains, which extend from the USA to Newfoundland, were formed by the collision of the African and North American plates. The Manuels River lies on the eastern edge of these ancient mountains, now largely eroded.
Nearly 200 million years ago, modern Africa started to separate from North America to form the present-day Atlantic Ocean, leaving the Avalon Peninsula behind as a remnant of ancient Africa.
The Manuels River river valley and the thin sediment that covers the bedrock are geologically very young. The original valley was shaped during the last ice age by a glacier flowing northward from the Avalon ice cap into Conception Bay. The glacier melted away about 10,000 years ago and left rock debris strewn over the landscape. Some large blocks of this debris are seen in the upper part of the valley, and cliffs composed of glacial sediment are found along the coast. Rivers produced by melting glaciers initiated erosion of the present gorge.
Sedimentary rock: most of the rock types seen along the lower Manuels River result from the erosion, transport and deposition of sediment from pre-existing surface rocks. Water, wind and ice transport sediment. Water and wind are able to sort sediment into uniform particle sizes, but most sediment deposited by glaciers is poorly sorted. Sediment becomes rock over time by burial below younger deposits. A sedimentary rock with fragments the size pebbles or cobbles is called conglomerate. Sandstone, siltstone and shale are successively finer grained sedimentary rock.
Igneous rock: crystallizes directly from molten rock, called magma. Granite solidifies at depth giving large crystals. Volcanic rocks are usually finer grained because of rapid cooling of lava at the surface. Some volcanic eruptions are explosive; hot lava fragments and ashes fall around the volcano, with some settling below water to form more stratified deposits.
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Sedimentary layers (beds) are deposited one on top of the other to form a 'succession', with the youngest on top. Stresses in the crust later cause tilting of the succession. The rocks of the Manuels River dip down to the North-North-West and so lie at great depth below Bell Island. The ironstones that were mined there are 20 million years (higher up the succession) that the rocks at Manuels River. The panel below shows a vertical geological cross-section from Bell Island to Manuels River.
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