60 Dr. Mac Culloch's Sketch of the 



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 dif- 

 ferent 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 ap- 

 pearance of having undergone the process of calcination. The coal 

 is rare, but occurs in different places, and its character in such situ- 

 ations 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 expe- 

 rience in similar situations*. The succession of these several sub- 



* I have since recrlvod similar specimens from Guadaloupe, where they occur among the 

 lavas of that island, adding one more to the numerous analogies already exit;ting betwcca 

 ihe volcanic loeks and the trap family. 



