Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/197



ADDENDA.

1. Account of certain porphyritic rocks of doubtful formation.

2. Alluvial formations.

Near the centre of the basaltic area, and about seven miles north north-east from Antrim, a very remarkable district occurs, in which a reddish variety of clay porphyry prevails.

This district is situated between Templepatrick on the south and Kells and Connor on the north, including an area of about four English miles; proceeding from Connor in a westerly direction, you first meet the porphyry formation at Camecome, scarcely a mile distant from that village, and continue upon it for about three miles, as far as the source of a small brook called Loonburn, which empties itself into the Six mile water above Templepatrick.

Numerous small hills are scattered over this tract; Sandy-brae, Brown Dodd, Tardree, Forthill, and Carnearny, are the names of the most considerable. These are all low hummocks, exhibiting in their outline a striking approach to regular segments of circles, and, as Dr. Richardson has well remarked, strongly contrasted with the basaltic ridges which every where surround the porphyritic area, and uniformly present an abrupt escarpment on the one side, and a gentle slope on the other. The hill of Sandy-brae rises 537 feet above Doagh, which, from its situation relatively to Lough Neagh, cannot be estimated at less than 200 feet above the level of the sea.

The clay porphyry of this district has a reddish brown basis, containing imbedded in it concretions of smoky quartz, earthy and glassy crystals of felspar, and olivine. Specific gravity 2,43.