SANDSTONE OF THE WESTERN COAST. 95 



Alsh and Loch Duich. In Sutherland the examples are 

 numerous, and may be witnessed at Loch Eribol and in 

 Glen dhu (Assynt) ; the substance in contact, and imme- 

 diately subjacent, being often that quartz rock which in the 

 same vicinity alternates with the red sandstone. 



The alternations of the two latter rocks are also frequent 

 in Sutherland; and throughout this country the quartz rock 

 forms an essential part of the series, as it does in Sky ; 

 occurring in so interspersed a manner that it is rarely 

 possible to distinguish the two on a map, however large its 

 scale. It is from this cause, apparently, that some of the 

 mountain summits in this tract present quartz rock sur- 

 mounting red sandstone, or occupying that position on 

 the gneiss which the latter rock does in Ross-shire. There 

 is indeed no reason to doubt that the quartz rock is here, 

 as in Sky, a part of the red sandstone series ; although 

 differing in no respect from that substance as it is found 

 alternating with micaceous schist in Isla and Jura. 



Lastly, it must be remarked with respect to the position 

 of the red sandstone, that it is often unconformable to the 

 gneiss. As it is unnecessary to multiply examples, I 

 need only say, that instances of this relative position occur 

 in Suil veinn, and in many other parts of the extensive 

 tract under review. In these, the gneiss lies at angles 

 considerably elevated, while the beds of sandstone are 

 nearly horizontal. Wherever the contact of the two is 

 to be observed in these cases, an intimate union will be 

 found to exist; the irregular surface of the gneiss being 

 filled with a breccia formed of its own fragments, strongly 

 adhering, as in the instances already mentioned in Lewis 

 and in Rasay, and the stratified structure of the sand- 

 stone commencing only after these irregularities are filled. 

 Whatever difficulty may be imagined to exist in explaining 

 this double relation which the sandstone possesses to the 

 gneiss, there is no reason to doubt the identity of the 

 whole deposit, as the points of connexion and continuity 

 are nevertheless of frequent occurrence. 



