364 7 ON THE CORALS OF THE 
hardened mud had been washed away from the calcareous 
nuclei; and I was not a little surprised to find, that the seem- 
ing concretions were massive corals, apparently all of one 
species, and evidently of the family Astreide. The masses 
in this unique bed, each a corallum, are of irregular form, 
but usually flat and oblong, and vary in size, from nine or ten 
inches in length by six or eight in breadth, to from three to 
four inches in length by from two or three in breadth ; while 
in thickness they vary from about two-and-a-half inches to less 
than an inch. They are thickly covered on all sides by shal- 
low polygonal calices, irregular both in size and form, for they 
vary from nearly half an inch to little more than a line and 
a-half in breadth, and -present from four to six sides. The 
dividing walls are thin, and not prominent, and each calice is 
traversed by from thirty to sixty septa of unequal size. A 
coral of the Inferior Oolite, Jsastrea tenuistriata, resembles this 
Tsastrea of the Lias more closely than any other fossil species 
yet figured ; but in the Oolitic Isastrea the calices seem to be 
more equal in size, and more regular in form; and, from the 
smallness and fragmentary character of the specimen given in 
the monograph, I was unable to determine whether it possessed 
what seemed to be the most marked characteristic of the Skye 
coral. In all the other species of Isastrea I have yet seen, 
each corallum has a determinate base, from which the coralites 
radiate ; whereas in the Liassic species they seem congregated 
together on all sides of the corallum (which appears to have 
had no base), like the cells in a honeycomb, and even cover 
wen-like protuberances on the general surface, in a way that 
precludes the possibility of their having radiated from any 
common axis or centre. 
The history of this coral bed of Skye, so unique in the Lias, 
seems to be simply as follows: In what is now the Inner 
Hebrides, as in other parts of the British islands, the Liassie 
