The paleontology or the study of the fossils of Hook Head is, if it be possible, even more interesting than its physical geology. As soon as ever we cross over the sandstones, and ascend into the higher strata of the Carboniferous series proper, we reach a domain abounding with animal life. Almost immediately above the sandstones which afford the remains of the fossil plants, we reach a zone having a distinct mineral character. This zone consists of a black shale, a substance which was originally black mud deposited by the sea, and this black shale is an important member of the great Carboniferous series of the south of Ireland. At Hook, it is a very degraded form of that member of the Irish carboniferous series known under the name of “carboniferous slate.” In this locality it has a thickness of only a few yards, but westward from Hook the carboniferous slate increases in thickness, until we find it in the county of Cork, separating the sandstone strata below from the lower portion of the carboniferous limestone above, by an interval, in some instances, reaching to about 4,000 feet. At Hook, this ancient muddy sea-bottom seems to have existed for a shorter time than towards the westward, and was succeeded by a sea containing a considerable portion of lime in its waters.