

DYKES IN CARBONIFEROUS ROCKS. 339 



posures connect it with Cockfield. This outburst is of post-jurassic 

 age ; Mr. Teall suggests that it may perhaps be Miocene. In chemical 

 composition it closely resembles the augite-andesites of the Continent. l 



The Hetts Dyke. According to Professor Sedgwick this dyke 

 ranges from the escarpment of magnesian limestone at Quarrington 

 Hill, east of Durham, in a W.S.W. direction by Tarsdale, Hetts, Whit- 

 worth, through the collieries of Bitchburn and Hargill Hill, and up 

 the Bedburn Beck valley to Egglestone Moor. The thickness increases 

 westward from 6J feet to 15 feet. At Hetts the dyke leads to the 

 north at a high angle. It bakes and indurates the rocks with which 

 it is in contact. It differs from the Cleveland dyke in wanting por- 

 phyritic crystals of felspar. Two miles to the north of the Hetts 

 dyke is another dyke of the same composition ; and there is a hori- 

 zontal sheet between the two at sixty fathoms below the surface. 

 Sedgwick regarded this dyke as palaeozoic. 



The High-Green Dyke. The High-Green dyke, which crosses 

 the Parret, runs west to east, and is 50 feet thick along the stream. 

 Its central part is coarsely crystalline. On the north wall it is 

 cellular. 



The Acklington Dyke. This dyke stretches from the coast at 

 Bondicar near Acklington, where it is 30 feet thick, through the Car- 

 boniferous rocks and Cheviot porphyrites, and runs for many miles 

 across the South of Scotland. It is well seen near Newton and 

 Chennel, about eighteen miles west of Acklington. 



The Hebburn Dyke, according to Professor Lebour, emerges from 

 beneath the magnesian limestone near Cleadon, passing W.N.W. by 

 Hedworth and Hebburn to the Tyne. The Coley Hill dyke, west of 

 Newcastle, is sometimes supposed to continue the line. This dyke 

 is 44 to 50 feet thick. It cuts no formation newer than the Coal- 

 measures. 



The Tynemouth Dyke is seen at Tynemouth on the shore 

 in contact with the Coal-measures. It is 10 feet wide, and divided 

 into two parts by a quartz vein 6 inches thick. Mr. Teall regards 

 the Coley Hill dyke as a part of the Tynemouth dyke. 



Bnmton Dyke. Professor Lebour traces this dyke 2 from West 

 Allendale over the South Tyne to west of Haydon Bridge ; over the 

 North Tyne, near Wall, to St. Oswald's chapel, near Brunton ; and 

 it is last seen in the Bingfield Burn ; so that its main direction is 

 from N.E to S.W. 



The Seaton and Hartley Dykes. Several dykes run parallel to 

 each other from N.W. to S.E., and are exposed on the shore between 

 Seaton and Hartley. The dyke near Seaton, according to Mr. Teall, 

 is 10 feet thick at the bottom of the quarry, 5 feet thick at the top. 

 Another of the dykes is occupied by a rubbly mass in the centre. 



The Morpeth Dyke is only seen crossing the Wasbeck, near 

 Morpeth. 



These are a few examples of dykes discussed by Mr. Teall, but 

 they indicate some of the general features of such phenomena. 



1 Teall, Q. J. G. S., vol. xl. 2 "Geology of Northumberland." 



