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ON THE CORALS OP THE

the plesiosaurus must have gambolled, and the goggle-eyedichthyosaurus have darted along the tracts now traversed bythe porpoise and the whale.

The Oolitic deposits in the neighbourhood of Helmsdaleconsist mainly of beds of a laminated, dark-coloured, arenace-ous shale (charged with ammonites and belemnites, serpulaand terebratula), which alternate with beds of a rough conglo-merate, formed chiefly, as has been already intimated, of OldRed Sandstone materials. The corals, especially those ofthe genus Isastrea, occur both in the shales and the con-glomerates ; but it is amid the rocky masses of which thelatter are composed that they seem to have grown • and inthe shale we not unfrequently find them overturned, as ifthey had been tom with violence from their proper habitatson some stony ridge or hard bottom, and buried head-down-wards in the mud. Corals, apparently of two different spe-cies, occur at Brora, but in so defective a state of keeping,that little else can be said regarding them than that theyseem to belong to the genus Thecosmilia. In both, the co-rallum is composite and dendroid; but in the one the branchesstrike off at more acute angles than in the other. Its calices,too, are more rounded at their edges, and its septa less sim-ple, more flexuous, and more prominently denticulated. Soimperfect is their state of preservation, that neither speciesexhibits the exterior coating or epitheca characteristic of thegenus. The place in the system in which they occur is higherthan that of the beds at Helmsdale, but not higher than thebase of the Great Oolite. And such are all the corals ofthe Oolitic system in Scotland with which the explorationsof years has brought me acquainted.

The other subject to which I purpose directing for a briefspace the attention of the Society has a connection, rather in-cidental than direct, with the fossil corals of our country. Onfirst acquainting myself, about ten years ago, with the massive