XOETHUMBERL.VND X^D DURHAM. 29 



in the river, and is there overlaid by a granular white limestone. 

 At High Force and Cauldron Snout the river cuts through it, 

 and tumbles over cliffs, exposing a limestone below, which is 

 metamorphosed, white and crystalline. This basalt extends 

 nearly as fai' as Middleton, but in the lower part, at a little 

 distance from the river. 



Throughout its long range the rock is essentially the same, 

 being composed of felspar and augite ; the iron entering into its 

 composition is in the state of a protoxide, and indeed occasionally, 

 as at the Parne, it possesses polarity. At Budle it is amygda- 

 loidal ; and at Ratcheugh some portions are porphyritic, having 

 large felspar crystals scattered through it. Wh.ere in great mass 

 the rock has a pillared structure, the columns being rude prisms, 

 irregularly jointed ; and some even approach the hexagonal forms 

 seen in Fingal's Cave. They are grand and impressive objects, 

 massive, though rude ; and, towering majestically to a great 

 height, we could imagine they had been piled up by the fabu- 

 lous giants of the olden time. 



The metamorphic action of the basalt on the strata above, as 

 well as on those below it, is favourable to the view, that the 

 Basaltic Sill is a lateral dyke intruded among the strata after 

 their deposition ; and the displacements of strata effected by the 

 eruption lead to the same conclusion. At the Fame Islands, 90 

 feet of limestones, shales, and sandstones have been torn from 

 the mass with which they were originally connected, and are 

 lifted up and altered in structure. At Howick, too, there are 

 evidences of violent mechanical action ; and near to Little Mill 

 there is a marked instance of the same character — for on the 

 western or basset side of the basalt, limestone and shales are 

 highly inclined against it : their dip is to the south-west from 

 60° to 45°, and the upper shale-beds are bent and thrown over ; 

 blocks of limestone, too, are enveloped in the basalt, and meta- 

 morphosed and penetrated with veins of the igneous rock, the 

 whole being firmly welded, as it were, into one mass. Though 

 in Northumberland this sill never appears anywhere, excepting 

 in the calcareous division of the Mountain Limestone, and gene- 

 tally among its upper beds, yet its position varies considerably 



