184 Dr. Berger on the Geological Feature i 



much iron and standing in a situation approaching to perpendicular 

 in many instances, might In time become natural magnets, with 

 the south pole uppermost and the north pole lowermost. 



This however, I have never found to be the case ; but I re- 

 marked a complete polarity in a rounded block of greenstone that 

 was lying rather deep in the ground on the top of Donald-hill in 

 the county of Londonderry : the needle of a pocket compass that 

 had been laid upon it went half way round and stood there per- 

 manently, the north pole of the needle pointing to the south and 

 the south pole to the north. 



The pillars of Fairhead, and the adjacent summit of Fairhead, 

 are composed of greenstone containing augite. 



Basalt passes Into greenstone in the most Imperceptible manner : 

 in the first stage, the felspar exists under the form of short, scaly 

 parts either white or greenish ; the texture becomes more finely 

 granular and crystalline; the fracture In the great Is not into flat 

 conchoidal pieces, but more usually into irregular and blunted 

 fragments. This finely granular and almost compact greenstone is 

 also more tough than common floetz-trap. 



3. Greenstone, 



It Is difficult to determine the precise geognostic relations of the 

 basalt and greenstone in this district ; but since the latter here 

 occupies an extent comparatively small. It must be considered as a 

 formation subordinate to the former ; whether however they form 

 distinct beds, or pass insensibly into each other by a gradual tran- 

 sition, is as yet undecided. 



The greenstone columns of Fairhead and Cross hill are destitute 



