I. Introduction. [C. A. M.] Although Carboniferous rocks form the rock-floor of the greater portion of the County of Dublin, they are so much concealed inland by Glacial Drift as to render their structure and relationships usually obscure. On the coast, however, they crop out in several very good sections, especially near Malahide, about 4 miles north of Dublin Bay, and at Rush, about 6 miles still farther north. The latter is the more extensive and interesting of these two. From the shore south of Rush village, extending northward past Loughshinny to within a mile of Skerries—a distance in all of about 5 miles—the Lower Carboniferous rocks are splendidly exposed: the outcrops being only interrupted occasionally, where the shore is covered by sand, or the Glacial Drift descends to sea-level. At the suggestion of Mr. G. W. Lamplugh, F.R.S., and tempted by the interesting character of the rocks themselves, I was induced (during a temporary residence in Ireland) to make a detailed examination of these beds. In order to understand the coast-section in full detail, a horizontal section of the beds, as shown in the cliffs and along the rocky shore, has been prepared for the whole distance on the scale of 1 inch to 10 feet. As, however, fossils have up to the present been collected only from the rocks near Rush, that is to say at the southern end of the line of section, the present communication will be restricted to that part of the area; but account