[CHAPTER XVI.]
The Pholas, &c.
(ROCK-BORERS.)
'He that of greatest works is finisher
Oft does them by the meanest minister.'
XVI.
At certain parts of the Scottish coast, the 'dykes,' or walls built near the road-side, are constructed entirely of rough-hewn pieces of hard sandstone rock, brought from the neighbouring shore. Sometimes a dyke will extend for two or three miles, without presenting an isolated fragment, in which the honeycomb-like perforations of certain species of the boring Mollusca are not more or less apparent.