| II. | Transition Rocks[1] |
| 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 accompanying
map (Pl. 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 rooting 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, Binty 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 intervening 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 sandstone 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.
