The Acklington Dyke is an igneous intrusion which extends from northwest of Hawick in southern Scotland east-southeastwards through the Borders region towards the North Sea coast of Northumberland in northern England.The dyke is associated with volcanism which took place at the Isle of Mull igneous centre in western Scotland during the early Palaeogene Period at a time of regional crustal tension associated with the opening of the north Atlantic Ocean and which resulted in the intrusion of innumerable dykes. The similar Cleveland Dyke has been dated to 55.8+/- 0.9 Ma. The dyke is composed of tholeiitic microgabbro and basaltThough generally thinner, it is up to 30 m wide in places. It is one of the most significant of a swarm of such intrusions associated with the Mull centre which extend