BASALTIC DYKE 171 



Having described all the strata, or flat rocks, of our district, it 

 now remains, that we attend to a rock of a different nature, which 

 intersects a large portion of them, viz. 



THE BASALTIC DYKE. 



This singular rock (marked r) crosses our alum hills in the 

 form of a vein, intersecting the strata nearly at right angles. It is 

 one of the most remarkable whinstone dykes in Britain, as it has been 

 traced on the surface to the extent of 60 or 70 miles, and is in some 

 places 70 feet wide, or upwards. It runs nearly in a direct line, 

 north-west and south-east, from Cockfield Fell in the county of 

 Durham, to Maybecks. 



In several parts of its course, the dyke protrudes to a consider- 

 able height above the surface ; as at tlie ridge called Parker's hone, 

 in Glazedale ; at a place in Lownsdale ; and especially at Cliffrigg, 

 and Langbargh, in Cleveland ; where it forms a very prominent ridge, 

 crossing the plain from the Avest side of Rosebury to the Tees, to 

 which it proceeds by Nunthorp and .Stainton. In other parts, it 

 barely reaches the surface, or rises a foot or two above it ; as in its 

 course from Maybecks to Silhoue, and its descent from thence to- 

 wards the Mirk Esk. In many other places, it does not reach 

 the surface, being covered by alluvium, often to a great depth. 

 Whether there be any spots where it is also covered by a part of the 

 regular strata, remains to be ascertained. In a quarry at Whitley near 

 Cullercoats, where there is an extensive mass of the magnesian lime- 

 stone, detached from the great beds of the county of Durham, there 

 is a similar dyke or vein, which intersects the coal and sandstone 

 strata, under the limestone, but does not pass through the latter. It has 

 been supposed that, in a similar way, our basaltic dyke passes under 



