DURHAM AND NORTHUMBERLAND. 2S

depth to the surface, are various in their qua-lities, and are distinguished under the namesof the whin-dykes, stone-dykes, clay-dykes,rubbish-dykes, and slip-dykes.

The whin-dykes are formed of basalt,* orwhin-stone, (one of which occurs at Coaly Hill,near Newcastle,) which, according to some the-ories, is supposed to have issued hot from thebowels of the earth ; indeed this idea is muchstrengthened by the coals on each side being re-duced to cinder, and continuing more or lessburnt or scorched to a considerable distance.The most striking instance of this phenomenonappears in a dyke passing from Ayton in Cleve-land, by Bolam, which is seven miles and ahalf north-west of Darlington, in a right line toCockfieldfell, in the county of Durham : itis of a black basaltic nature, and is quarriedfor the purpose of mending the roads, makingthe firmest foundation possible.

The stone dykes are filled with a variety ofimperfect materials, which in general areboth hard and dry, and separated by fissures

* According to Werner, basalt is confined to the Floetz-trap, or secondary trap formation. It occurs in vastmountainous beds, mostly of a conical form, in strata,in banks or dikes, and in veins, and almost always ac-companies coal. Aikin’s Chem, Diet. — D’Aubuisson .