Mineralogy of Sky, 165 



usual place in the one case as the graywacke is in the other. But 

 the island of Sky is very often unsystematical : that which follows 

 perhaps still more so than that which has preceded. 



In attempting to trace the red sandstone below, or rather beyond 

 the white quartz rock, it is not found to terminate on the north- 

 western shore of Sleat, at the place where, according to the line of 

 direction prolonged from Isle Oransa, it should end. Instead of 

 that, the alternations of sandstone and schist continue. Gradually 

 however they increase in frequency, and becoming at length undu- 

 lated and contorted, they cannot at a distance be distinguished from 

 gneiss in their general aspect and disposition. In examining the 

 substances, the first alteration perceived is the gradual induration 

 of the sandstone, which becomes first a compact quartz containing 

 grains of red felspar. At length the felspar acquires a laminar 

 tendency, the schist still remaining unchanged, the rock thus 

 becoming an irregular gneiss (if it may be so called) consisting of 

 laminse of quartz, felspar and graywacke schist. Approaching the 

 point of Sleat the schist gradually becomes green and glossy, thus 

 passing into chlorite slate, and here we arrive by an insensible 

 gradation to the variety of gneiss which I formerly described as 

 found there. In thus pursuing the red sandstone on the western 

 side of Sleat, the reason appears why I could not when speaking of 

 that rock, define the boundary of the gneiss on this side of the 

 island, and I need now scarcely repeat, that any attempt to examine 

 rocks so constituted, in the interior country, would leave nothing 

 but doubt and uncertainty ; for which reason I have limited the 

 description to the sea coast, where every foot of the rock through 

 all its transitions admits of free examination. 



I have no commentary to offer on these facts, which seem cal- 

 culated, if not to excite disbelief, at least to set our present systems 



Vol. iv. y 



