Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/171

 attains the elevation of 450 feet above the sea; in the adjoining mountain called Donald's hill, its upper limit rises to 900 feet; it occupies nearly the same level in Benbradagh, and at Cragnashoack the southern point of the chain gains its greatest height, being there 1589 feet above the sea. In this mountain the sandstone and basalt are in contact, the chalk being deficient. Cragnashoack and Fairhead are, it is believed, the only instances in this district where the trap is seen decidedly reposing on any other rock than the chalk.

The sandstone of Benyavenagh, of Kedy and of Donald hill, is red, slightly variegated with yellowish stripes of a rather loose texture; it has a calcareous cement, and contains specks of mica.

The sandstone of Benbradagh has the character of sandstone slate, the texture coarsely granular; colour greenish white; with a calcareous cement, and containing spangles of mica. It extends to Dungiven, and probably reposes on the mica slate, which occupies the left bank of the Roe; its thickness in this hill cannot be less than five hundred feet. About a quarter of a mile from Dungiven, at the opening of Benady glen a sandstone conglomerate occurs, probably connected with this formation,

The insulated primitive district of Coolcroscrahan, which is situated behind Benbradagh on the north east, appears to be encircled with a ring of sandstone and marle.

In Cragnashoack, two varieties of sandstone may be traced, the upper beds consisting of a coarse grey sandstone with a calcareous cement, while the lower strata are more distinctly slaty and micaceous, and have a yellowish colour and a siliceous cement.

From Cragnashoack the sandstone extends to the south, abutting on the north Cast slope of Slieve Gallion. Near this point it appears to repose upon the shell limestone of Desert Martin, ranging from