346

ON THE CORALS OF THE

round, concealing their true character; but where the edge ofthe bed was exposed to the lashings of the surf, the hardenedmud had been washed away from the calcareous nuclei; andI was not a little surprised to find, that the seeming concre-tions were massive corals, apparently all of one species, andevidently of the family Astreidae. The masses in this uniquebed, each a corallum, are of irregular form, but usually flatand oblong, and vary in size, from nine or ten inches in lengthby six or eight in breadth, to from three to four inches inlength by from two or three in breadth; while in thicknessthey vary from about two-and-a-half inches to less than aninch. They are thickly covered on all sides by shallow poly-gonal calices, irregular both in size and form, for they varyfrom nearly half an inch to little more than a line and a-halfin breadth, and present from four to six sides. The divid-ing walls are thin, and not prominent, and each calice is tra-versed by from thirty to sixty septa of unequal size. A coralof the Inferior Oolite, Isastrea tenuistriata, resembles thisIsastrea of the Lias more closely than any other fossil speciesyet figured; but in the Oolitic Isastrea the calices seem tobe more equal in size, and more regular in form; and from thesmallness and fragmentary character of the specimen givenin the monograph, I was unable to determine whether it pos-sessed what seemed to be the most marked characteristic ofthe Skye coral. In all the other species of Isastrea I haveyet seen, each corallum has a determinate base, from whichthe coralites radiate; whereas in the Liasic species they seemcongregated together on all sides of the corallum (which ap-pears to have had no base), like the cells in a honeycomb, andeven cover wen-like protuberances on the general surface, ina way that precludes the possibility of their having radiatedfrom any common axis or centre.

The history of this coral bed of Skye, so unique in theLias, seems to be simply as follows :—In what is now me