The specimens that accompany this paper will shew to the common observer the difference between the limestone when in contact with, or at a distance from the dyke, as well as that between the dyke itself and the ordinary whin rocks of the county, such as those which are found on the Cheviot, and which form large masses on that range. Indeed all the whin dykes that I have seen in the northern district of Northumberland, the two which are so near to each other in Holy Island, and those which form the Fairn Islands, no less than that at Beadnel, bear a striking and uniform resemblance to each other; and are unlike those ranges of whin which are composed principally of hornblende, and which prevail to such an extent in the north-western parts of the county.
