Geology of the Isle of Man

The older strata was folded and faulted during the Caledonian and Acadian orogenies The bedrock is overlain by a range of glacial and post-glacial deposits.

Igneous intrusions in the form of dykes and plutons are common, some associated with mineralisation which spawned a minor metal mining industry.

A celebrated site in the far south is 'The Chasms' where large fissures have opened up in the coastal cliffs of the Mull Hill Formation's quartz-arenites.

The Niarbyl rocks which were found on the basis of a graptolite discovery, to be of Wenlock age as recently as 1997 constitute the sole formation within the Dalby Group.

[6] A scatter of diorite and lamprophyre dykes were emplaced during the early Devonian, the latter within the Niarbyl Formation rocks south of Peel.

The limestones were formed in the Eubonia Basin,[7] occupied by a tropical sea as the Isle of Man was situated at the equator at this time.

The only onshore representatives of this basin succession, these strata are found within three miles of Castletown; inland exposures are few but these rocks are well exposed along the coast between Kentraugh, east of St Mary and the Santon Burn south-east of Ballasalla.

At the top of the Carboniferous sequence, a suite of igneous rocks which outcrop on the eastern side of Bay ny Carrickey opposite Port St Mary which include tuffs, pillow lavas and debris flows are collected together as the Scarlett Volcanic Member.

Olivine microgabbro dykes of Palaeogene age and with a broad NW-SE alignment are commonly exposed around the island's rocky coasts.

The Niarbyl Fault exposed in the cliff at Niarbyl on the west coast is considered to represent the Iapetus Suture, the welding together of the former continents of Laurentia and Avalonia in the course of the Caledonian Orogeny; sediments forming the rocks on one side of the fault were deposited on one continent, those on the other side were deposited on the other.

Lead, copper, zinc, silver, nickel and iron mineralisation has taken place in certain areas, notably around Foxdale, up Glen Mooar at Laxey and in the south of the island.

Vein deposits are especially associated with steep faults in Manx Group rocks with galena and sphalerite being the main ore minerals.

There are extensive areas covered by sands and gravels of glacial origin including sandur deposits and moraines not least in the flat north where they are known collectively as the Jurby, Orrisdale and Shellag formations.

There are less extensive spreads of such materials between Peel and St John's and north of Castletown and extending west to Port Erin.