Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/220

 range of promontories in the neighbourhood of the Giant's Causeway, commences. Since the chalk, which is here placed on the same level with the highest of these strata, must certainly in its regular place occur beneath the lowest, and since the whole series has been ascertained considerably to exceed 400 feet in thickness, the subsidence of the basaltic mass at this point must have been very great.

The neighbourhood of the causeway, with all its remarkable features, its superb storied façades, distinguished by a double order of columns, its whin dykes and its caverns, have been so fully and ably described by Dr. Richardson in the Philosophical Transactions, that they are already familiar to every reader interested in such subjects. His list of the strata here ascertained has been already given, page 177. On the strand near the mouth of the Bush, are two parallel ledges of chalk and basalt.

The appearances of the cliffs between Bushfoot Strand and Portrush Strand, are so similar to those which we have already found frequent occasion to notice, that this part of the section does not appear to require further elucidation. Near the termination of the chalk cliff on the west, a very inexplicable phenomenon presents itself; a large spherical mass of basalt, appearing to be completely enveloped in the chalk.

The singular peninsula of Portrush demands more particular attention; a long line of strand separates it on either side from the cliffs which rise at about the distance of a mile to the east and west.

The peninsula itself, which may be about a mile in circumference, is fenced with low cliffs on the west, north, and east; those on the west present a rudely prismatic greenstone; those on the north and east tabular masses of greenstone, overlying, and in