570 



ERUPTIVE AND METAMORPHIC ROCKS. 



Dyke traverses the Bernician rocks on the coast further south. In the north of 

 England the term Dyke is hkewise applied to faults ; thus the Burtreeford Dyke, 

 so named from Burtreeford in Weardale, and which occurs also in Teesdale, is 

 simply a fault that displaces the strata at some points as much as 800 feet.'' 



There are many other Dykes of Eruptive rock in the north of England which 

 have been fully described by Mr. Teall. 



The Cleveland, Cockfield, and Armathwaite Dyke commences six miles south of 

 "Whitby, and extends across the Eden Valley, a distance of more than 90 miles in a 

 W.N.W. direction. It is intrusive in the Lias and Oolites, and is probably of 

 Tertiary age. It is a dark grey or bluish-grey rock, an augite-andesite, 18 to 80 

 feet wide, and sometimes forms a conspicuous feature in the landscape. In some 

 localities where it does not reach the surface it has been proved in colliery 

 workings ; but coal in proximity to the eruptive rock becomes anthracitic and 

 ultimately worthless. The rock is quarried in many places.- (See p. 181.) 



Fig. 97. — Diagram Section at the High Force, Teesdale. 

 (C. T. Clough.) 



South. 



North. 



C. Basalt. 



B. Sbale 14 to 20 feet. 

 A. Limestone. 



Yoredale Series. 



The Ilett Dyke extends from the escarpment of Magnesian Limestone at 

 Quarrington Hill, east of Durham in a W.S.W. direction, through the Coal-field. 

 It occurs in the Coal-measures, but does not, however, penetrate the Permian 

 strata. It consists of diabase, which is probably contemporaneous with the rock 

 of the Great Whinsill. In thickness it varies from 6 to 15 feet. It was formerly 

 quarried between Tudhoe and Hett, and has subsequently been worked by shafts. J 



The High Green Dykes rear Bellingham are formed of Diabase. The Ackling- 

 ton Dyke penetrates the Carboniferous rocks at Broomhill Colliery near Acklington. 

 It has a thickness of about 30 feet, and is composed of Augite-andesite, and has 

 been traced westwards into the Cheviot porphyrites. This Dyke also is probably 

 of Tertiary age. The Dykes of Morpeth, Hebburn, Tynemouth, Brunton, Seaton, 

 and Hartley are composed of Melaphyre, and closely resemble one another. The 

 Hebburn Dyke emerges from beneath the Magnesian Limestone near Cleadon, 

 and passes in a N.N.W. direction by Hedworth and Hebburn to the Tyne at 



1 W. Gunn and C. T. Clough, Q. J. xxxiv. 27. 



* J. J. H. Teall, Q. J. xl. pp. 210-238 ; see also C. F. Strangways and G. 

 Barrow, Geol. Whitby and Scarborough (Geol. Surv.), p. 50 ; and J. W. Kirkby 

 and J. Duff, Nat. Hist. Trans. Northumberland, iv. 193 ; Lebour, GeoL North- 

 umberland, ed. 2, 1886. 



