some of them rarely, if ever, any where else. They were too small in quantity, and too little connected to admit of a place among the stratified rocks. These are iron-clay, coal, siliceous schist, and a particular sort of jasper. They occur separately or together in different places, but the whole are very conspicuous at Talisker. They are all extremely irregular in their positions, and discontinuous in their lateral extent. The iron clay is the most abundant of these, and forms considerable beds in the cliffs about Talisker, and along that coast as far as Loch Brittle. It is of various colours, red, purple, blue, and gray, and these are often very lively, giving to the cliffs the appearance of having undergone the process of calcination. The coal is rare, but occurs in different places, and its character in such situations is so well known that it is unnecessary to describe it. The siliceous schist is not abundant, but it is found in its most ordinary form, and also in that very remarkable concretionary globular shape, which having described at full length in speaking of the Shiant Islands I need not repeat here. The jasper is rare. I have used this term because I know of no other by which it can so well be characterized. It is yellow or brown, with a lustre approaching to resinous, and is well known as a product of the volcanic island St. Helena. The specimens of Sky differ in no respect from those of this island, which have sometimes, but improperly, been called pitch stones. That they are not such, if proof were necessary, would be sufficiently proved here by the regular gradation which they undergo into clay, appearing indeed to be portions of clay which have undergone changes in consequence of their vicinity to the basalt, resembling the well known ones which sandstones experience in similar situations[1]. The succession of these several substances
- ↑ I have since received similar specimens from Guadeloupe, where they occur among the lavas of that island, adding one more to the numerous analogies already existing between rhe volcanic rocks and the trap family.
