38 Dr. Mac Culloch's Sketch of the 



found, formed of large gravel or even of fragments, but I have not 

 seen either in Sky, in Soa, or in Rum, any regular beds of conglo- 

 merate connected with it, although I have in these situations had 

 repeated access to the whole thickness of the rock. Although the 

 general colours of this rock are such as I have described, yet it 

 seems occasionally, like the lowermost red sandstone in other places, 

 to contain portions of a different complexion ; one portion of such 

 a bed is seen under Garsven opposite to Soa, where it is of a white 

 colour and intermixed with decomposed felspar, yet still exceedingly- 

 compact. Pebbles of quartz and granite are imbedded in some of its 

 lamiuce. For the sake of those who contend for the doctrine of 

 universal formations of rock, I have recorded the whole of its cha- 

 racters and connections that they may have opportunities of com- 

 paring them with those of other similar rocks, and I can only add 

 to what I have here said, that as I imagine Rum and Sky to contain 

 portions of one common bed, so I am inclined to think that the 

 red sandstone which I have found on the western coast of Scotland 

 in various places, from Loch Ewe to the Ru Storr, appertains to 

 the same series of beds. It is still the same sandstone, as I imagine, 

 which extends to the east coast and finally to Orkney. 



The next bed in order is a bed of limestone, the investigation of 

 which was attended with more labour and doubt than that of all the 

 other rocks of Sky, and of which the. history I am about to give 

 cannot appear less credible to others than it did at first to myself: the 

 demonstration which I at length procured and shall now lay down is 

 however such as to admit of no dispute. It is important in a 

 general view since it shows us how little reliance can be placed on 

 internal characters in assigning the positions of rocks in the system, 

 and since it may possibly lead the way to the explanation of those 

 anomalous limestones to which the examples occurring near Ply- 



