Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne (1867).djvu/40

24 Megaceros Hibernicus, Cervus Alces, Cervus elephas, the wild boar, and remains of a horse.

There are two groups of igneous rocks in this district, of different age and mineral composition—the felspathic and the augitic; or the porphyries and the basalts; the former being of a much greater age than the latter.

1. Porphyry.—The Cheviots, a range of hills protruding through, and rising high above, the stratified rocks in the northern part of Northumberland, and extending into Roxburghshire, are composed of porphyry, which, however, varies in its character. Usually, the rock is a porphyrite, with a red felspathic base, in which are scattered crystals of felspar. In some parts it is a dark coloured dolerite, composed of labradorite and augite; and near to Yetholm it is a pitchstone porphyry. Not unfrequently it passes into a syenite, a crystalline compound of felspar, hornblende, and mica; and in some few cases it becomes a granite, formed of felspar, quartz, mica, and a little hornblende. On the north side of the Cheviot, in the Diamond Burn, there are masses of quartz rock in which appear crystals of quartz, some white or translucent, and a few others brown or amethystine. On the Ridlees Burn, where stratified rocks abut against it, the porphyry is amygdaloidal, with geodes, in which are developed fine quartz crystals, or which are filled with agates and calcedonies. The great mass, however, is felspathic.

The boundary line of this porphyritic range begins on the borders, at Presson, and goes eastward to Brankston, where the battle of Flodden was fought; it then bends southward to Yeavering, and by a series of undulations passes by Akeld, Wooler, Ilderton and Brandon, to Ryle, whence it bends westward to Prendwick, and thence, in a south-west direction, crosses the Coquet, above Linn Brig, to Ridlee Hill; after which it bends to the north-west, and crossing the Coquet again, above Philip, extends into Roxburghshire. Another part of the range is prolonged from Roxburghshire into the north side of the Reed above