SKY. GEOLOGY. SILICEOUS SCHIST. 355 



not have been examined without interrupting the order 

 of the preceding account. These are, siliceous schist, 

 chert, and coal; and as the two former occur in the 

 same circumstances, and occasionally in conjunction, their 

 history may in a great measure be united. 



These are found in detached fragments under the 

 high cliffs on the eastern shore of Trotternish, oc- 

 curring in considerable abundance and variety among 

 the fragments of the common strata that strew this 

 beach. The coast is very difficult of access even in 

 fine weather, and with a wind off shore ; in other cases 

 it cannot be approached, and, as the cliffs are perpen- 

 dicular and inaccessible, the natural position of these 

 substances cannot be discovered even after a successful 

 landing. As it is only by the colours, the dimensions 

 of the strata, and similar indications, that we can judge 

 of the nature of the different rocks in these cliffs, there 

 are no means of distinguishing between those beds that 

 consist of common shale and those that may be formed 

 of siliceous schist, and we must therefore be here 

 content with examining the fallen fragments. But as 

 these substances are accessible in other parts of Sky, 

 disposed among the ordinary strata and accompanied in 

 the same manner by trap, we are justified in con- 

 cluding that they exist in the eastern cliffs in the same 

 positions. 



The siliceous schist presents various tints, varying from 

 a pale to a dark grey and to an intense black. Occa- 

 sionally the two colours are found disposed in stripes 

 perfectly even and parallel, presenting a singular ap- 

 pearance when long rolled on the beach, as the grey 

 variety becomes white on weathering while the black 

 retains its original hue. On fracture, the cause of this 

 appearance is found to consist in the alternation of laminae 

 of different colours; many of the fragments resem- 

 bling striped jasper, some of the well-known specimens 

 of which are evidently but varieties of this substance. 



