50 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Near the middle of the first or northernmost mass of trap, and 

 entirely insulated by it, a patch of limestone was found. This 

 was in some parts attenuated to a thin lamina, and in others ter- 

 minated in long and slender strings. It was imbedded in the 

 trap to the depth of about a foot. 



As to the mineralogical character of the Bleadon trap, it is of a 

 reddish-brown, or greenish-grey colour, and is usually traversed 

 by veins and strings of calcareous spar, which often pass into 

 yellow crystalline limestone. It contains, in abundance, small 

 spherical kernels of calcareous matter, which are usually coated by 

 red oxide . of iron. Less frequently it contains steatite, and still 

 more rarely glassy felspar. The rock is rather tough than hard, 

 and decomposes so freely, that specimens of it adhering to the 

 limestone are not readily procured. 



The altered limestone has lost its original blue tint, and, in pro- 

 portion to the alteration it has undergone, has become, first, light- 

 red; secondly, buff; thirdly, bright deep yellow; and lastly, deep- 

 red. In all its bright and deep-red stages, it is crystallised into 

 obtuse rhomboids, like calcareous spar, into which it passes. All 

 the above gradations are frequently seen in the same bed. From 

 its original state of extraordinary hardness the altered limestone 

 has become very crisp and brittle. 



The distance from the trap to which the alteration of the lime- 

 stone extends, is from 5 to 25 feet. 



The author is of opinion that the principal shifts, faults, and 

 dislocations which are observable in the limestone beds at Blea- 

 don, took place prior to the intrusion of the trap, and are not 

 attributable to. that intrusion. In two instances, however, joints 

 are observable which run through the limestone and the trap con- 

 tinuously; though they are more obscure in the latter than in the 

 limestone. * 



Reasoning on the preceding facts, the author states his inability 

 to account for them, on the supposition that the trap was injected 

 or forcibly intruded into its present position. 



Referring to the southernmost mass of trap, visible on the west 

 side of the cutting, it will be seen that the outlines of the limestone 

 on the southern and northern margins of the trap do not corre- 

 spond ; so that it cannot be supposed that the beds have been 

 parted asunder ; nor do the beds adjacent announce anything of the 

 sort. If it be supposed that the limestone, which filled the space 

 now occupied by the trap, has been forcibly removed, the over- 

 lying beds bear no evidence of any displacement at all ; the deep 

 acute-angular indentations of the mass would be very unfavourable 

 to such removal ; and there is no mass of limestone visible above 

 or elsewhere, which in any way agrees in form with the mass of 

 trap. 



If it be supposed that the trap was injected into some previously 

 existing cavities, into the hollows and inequalities of which it be- 

 came moulded, that would not account for the extent to which 



