Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/184



In Carintogher and Cragnashoack the chalk appears to be wanting, and the basalt to repose immediately on the sandstone; but in the insulated mass of secondary strata which cap the primitive mass of Slieve Gallion (on the south of the great valley of denudation, through which the Mayola flows) the chalk again appears underneath the basalt, and there attains its greatest elevation, being quarried at the considerable height of 1460 feet above the level of the sea, the deposit is however thin and the strata much split.

On the east of Slieve Gallion is a valley about three miles in breadth, occupied chiefly by red sand and marle, and succeeded near Moneymore by a ridge of elevated ground, exhibiting chalk, rising over the sandstone and surmounted by basalt; this ridge rises from Lough Neagh. At Ruskey it is but little raised above the level of that lake; it ranges in a direction towards the north, passing a little to the west of Magherafelt, a continuation of it may be traced to the east of the insulated primitive district of Coolcoscrahan, thence bending round the source of the Kelvin, and joining the lofty chain before described near Ballyness. The western escarpment of this ridge may be considered as limiting in that direction the great basaltic area. Benbradagh, Cragnashoack and Slieve Gallion, which lie without the boundary so assumed, forming insulated and outlying masses, separated from the principal and continuous basaltic region by vallies of denudation.

The elevation of this ridge does not appear to be very considerable; it seems probable that the mulattoe will be found underlying the chalk in this ridge as it does in the hills with which it is connected from Ballyness to Benyavenagh.

The south western limit of the area of chalk would be determined by a line from Moneymore to Magheralin, this passes diagonally across Lough Neagh, the strata which occur along it are of course concealed