274 TRAP OF CORNDON, WOFERTON, CREST HILLS, BLACK KNOLLS, ETC. 



42. 



In the Crest Hill and Black Knolls are the following varieties of trap : 



1. Compact felspar rock. 2. Do. porphyritic. 3. Do. porplryritic and concretionary, with grains of hornblende, crystals 

 of common felspar, and iron pyrites. 



Near the Crest Hill some of the traps exhibit clear proof of having been intruded into the shale 

 posterior to its consolidation, particularly in the ascent from Wotherton, where a porphyritic felspar 

 rock b bursts up through shale a containing graptolites, in the singularly irregular forms exhibited 

 in this diagram. 



43. 



This shale could not originally have been deposited in its present highly contorted and broken 

 form : but the peculiarity of the intrusion consists in this, that although the shale is much fractured 

 yet it is wholly what geologists would call wwaltered, being as soft and thinly laminated as if the 

 layers were in their original position. Here, therefore, where from the condition of the beds of 

 schist, and the irregular forms of the trap, there can remain no doubt as to the latter having been 

 forcibly intruded, we see that circumstances which we are unable to explain have prevented the 

 induration of the schistose strata so common in similar cases. Another line of trap, which must 

 have aided in elevating the ridge of Meadow town, terminates near Leigh Hall, and is instructively 

 exposed in the centre of Whitsborn Hill, (PI. 32. fig. 2.) at the north north-eastern end of which 

 it is largely quarried as a road stone. 



44. 



The trap has a maximum width of forty feet, but diminishes in parts to about twenty-four feet, 

 and is arranged in irregular columnar masses c, the ends of which are, as in the Kin ton dyke, at 

 right angles to the highly inclined beds of schist d. These beds lie immediately on the western side 

 of the great axis of the Corndon, of which Whitsborn Hill is one of the north-north-eastern spurs. 

 The trap consists, for the most part, of a dark greenstone, made up of felspar and hornblende, with 

 veins and flakes of white carbonate of lime, with thin films of asbestus, and crystals of iron pyrites. 

 This passes in the centre into a fine, hard greenstone, which, although without veins, contains car- 

 bonate of lime minutely disseminated. Another variety is a grey felspar, of a rough fracture, whilst 

 the exterior of the band is in parts a grey porphyritic compact felspar. These varieties show that 

 even in a mass of this size, it is difficult to assign any one descriptive name to the rock. We may 

 safely term this a dyke, although I am disinclined to use that term without explaining that the 



