Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/160

 in that direction. Were the sea to retire a few fathoms and disclose the foundations of Rathlin, we should very probably discover the trap which constitutes the present surface of that island, resting on the old sandstone; and that rock in its turn reposing upon syenite.

.

A. Limestone underlying the Coal formation.

B. Coal formations.

C. Sandstone formations.

D. Lias.

E. Green Sandstone or Mulattoe.

F. Chalk.

A. ''Limestone The limestone here described appears to constitute a portion of that great limestone formation which may be traced through the counties of Kilkenny, Kildare, Dublin, the Meaths, Roscommon, the soutlr-east of Mayo, Sligo and Fermanagh. The great coal districts of Kilkenny in the south, and of Lough Allen in the north, repose upon it; as also do those of Dungannon and Cool Island described in the next article.

The points described in the text are principally situated on the north-west of the coal formations last mentioned, and near the line separating the sandstone associated with the coal, from the primitive mountains connected with the great chain of Londonderry.

On the south of these coal districts the limestone is yet more extensively displayed, intervening between them and the northern boundary of the greywacke district in Armagh: it is here exhibited skirting the banks of the river Blackwater above Charlemont for several miles; and the country on the south and south-east between Charlemont, Loughgall, Kilmore and Armagh, is principally occupied by this limestone. On the east of this district near Hillsborough and Lisburn, it seems probable that the sandstone and greywacke come into contact, the limestone being wanting: but still farther in the same direction, at Cultra and Holywood, on the southern shore near the middle of Belfast Lough, the limestone again appears in a position intermediate between the sandstone and greywacke, but probably not in immediate contact with the latter, a red sandstone of older formation being said to occur in the interval. This limestone is of the magnesia variety, (which also occurs in the same formation Dublin) its texture compact, but not crystalline, its fracture granular, its colour ochre yellow; it contains cavities lined with calc spar, and presents organic remains: the thickness of the beds varies from one to six feet. underlying or associated with the Coal Formation.''

At the entrance of Cookstown on the road from Coagh, there are quarries of a shell limestone formation supposed to extend itself to the south as far as to Steward's town, and nearly for one mile in the other directions: it is disposed in strata alternately