arisaig

The rocks at Arisaig began about 450 million years ago when major volcanic activity produced basaltic and rhyolitic lava flows, ash flows and ejected material (tufts). Shallow tropical seas, teeming with life, flooded the land and left deposits of fossiliferous shales and siltstones. The bank to the left of Arisaig Brook is the site where a large number of fossils have been found.

The cliffs at Arisaig are made of very thin layers of sediment and erosion is constant. The picture on the right shows the tiny fragments of the layers at the base of the cliff.

It contains an almost continuous 2500 m thick record of shallow marine sedimentation, representing a span of almost 30 million years. The 15 km of coast, from Arisaig Point to McAras Brook, expose a total of 47 million years of earth history.

These rocks contain brachiopods, graptolites, pelecypods, trilobites, crinoids, cephalopods, ostracods and bryozoa, indicating shallow marine to brackish-water environment.

	Gastropods (snails) that look much like today's snails are found, but one form had a coiled shell that flared very wide at the bottom. This adaptations may have enabled them to move on the mud bottom. Most snails are found in the limestone formations.
Nautiloids or horn shells were predators related to the modern squid. They had a cone-shaped shell with chambers inside. The chambers held air to provide buoyance for swimming. Some nautiloids had been found reaching 30 cm in length. They were powerful predators.
	Sea lilies, or crinoids, were filter-feeding animals that lived attached to the sea bottom by a thin stalk. At the top of the stem, a plate-covered body with ten or more feathery tenacles collected food. You normally find sections of stem, which look like stacks of small coins.

Arisaig Underwater Life

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