146 Dr. Bergfr 0// the Geological Features ' 



II. Transition Rocks.* 



A. Greywacke. 



B. Transition limestone. 



C. Transition trap. 



D. Old red sandstone. 



A. Greywacke and Greywacke Slate 



occupies a great part of the baronies of Ardes, Castlereagh, and the 

 two Iveaghs in the north of the county of Down, whence they 

 extend through Armagh and Monaghan into Cavan. The accom- 

 panying map (PI. 8.) will convey a sufficiently accurate idea of 

 their extent. Their characters do not differ from those which 

 they exhibit in other countries already frequently described. 



The greywacke slate is worked extensively for roofing slate at 

 Ballyalwood in the center of the peninsula of Ardes : a variety 

 however, still better adapted to this purpose, remains yet neglected 

 at Cairn Garva, on the west-south-west of Conbigg hill. 



At Cultra, on the north-east of Belfast lough, flinty slate and 

 drawing slate occur as subordinate formations in the greywacke. 



Lead and copper ores have been found in this formation at 

 Conbigg hill, between Newtown Ards, and Bangor, and I believe 

 at some other places. A mine was formerly worked at Conbigg, 

 but is now abandoned. 



* The term transition is here employed merely as the name of a class of rocks inter- 

 vening in their position and intermediate in their character between the primitive and 

 secondary classes, no other or hypothetical meaning is attached to it. The old red sand- 

 stone here described, has been associated with these rather than with the secondary rocks, 

 because it appears in one instance at least to alternate with greywacke. 



