IV. On the Dykes of the North of Ireland, 



By J. F. BergeRj M.D. Member of the Geological Society. 



Read November 4thj 1814. 



M' 



.Y object in the following paper is to describe some of the 

 more general characters of Dykes, such as I have lately observed 

 them in the North of Ireland. 



I do not know exactly within what geographical limits these 

 curious geological phenomena are to be met with : they are com- 

 mon on the Western coast and in the Isles of Scotland, and I have 

 observed them also in the Isle of Man. I understand that none 

 have yet been remarked in the South of Ireland, and I did not 

 observe any in the Midland counties through which I passed be- 

 tween Dublin and the Northern coast. In England they have 

 been found in the centre of the island, as at the colliery of Tividale 

 in Staffordshire ; but in the North of Ireland it is only on the verge 

 of the coast that they abound, and it is there that I have principally 

 examined them. Of more than sixty that I noticed, nearly half 

 were situated on the shore ; those which occur in the mountains 

 of Donegal are I believe the remotest from the sea, and those lie 

 within fifteen miles of it. 



I have not found their occurrence to depend upon the absolute 

 elevation of the country in which they appear. I have observed 

 them at almost every altitude between that of the shore and those 

 which I have inserted in the following Table, as being the greatest 

 and somewhat uncommon. 



