Dr. M*=Culloch's Supplementary Remarks on Quartz Rock. 55 



while some present the colour and, except in their superior compactness^ the, 

 aspect of red sandstone. A few are mottled with red and white^ in spots^, 

 stripes^ or irregular stains^ such as are well known to occur in many varieties 

 of the lowest red sandstone. This is in fact an instance of the association of 

 quartz with the primary sandstone described as occurring in Sky. 



This mass is followed by a similar gneiss to that which lies below it, and 

 which not only forms the principal part of Ben More^ but extends in succession 

 to the head of Loch Shin, and so on, to a distance which I need not here 

 specify. This is the most conspicuous and satisfactory alternation found in 

 these hills, but not the only one ; since, in crossing the ridge to Loch More, 

 the quartz rock is again found on one of the inferior summits. There are no 

 obvious means, however, of determining whether this mass also alternates 

 with the gneiss ; nor did it appear of such moment as to call for a laborious 

 search, as the fact is sufficiently proved by the appearance of the beds on the 

 shores of Loch Dhu. 



Similar arrangements are seen on the south side of that inlet of the sea 

 which flows through the Cylescuagh, into Glendhu and Glencoul, and which 

 is without a name. 



It is unnecessary to dwell more particularly on these ; since the alternation 

 of the gneiss is established in a similar manner, by the positions of both rocks, 

 and by the conformity of their dips ; while the mineral characters of the. 

 quartz rock are the same as those of the beds already described. The object 

 of this paper not being of a geographical nature, I shall not at present trace 

 the quartz rock further ; since better opportunities of entering fully into this 

 branch of the subject will hereafter occur. 



It would have been desirable, in the particular instance first described in this 

 paper, to have traced the actual contact of the gneiss and quartz rock where 

 the alternation is most demonstrable: but, unfortunately, as is too often the 

 case, the nature of the ground does not admit of it. Those parts of the hills 

 where the rocks are bare, and where these contacts should be seen, are pre- 

 cipitous and inaccessible ; while the flatter, are, from their more gentle decH- 

 vity, covered with an impenetrable mass of rubbish. In every respect indeed 

 the country is of the most difficult access. But the contact in question and 

 the nature of the transition, though they cannot be seen here, are to be 

 found in many other situations where the two rocks exist together. They 

 can thus be traced in Ben Ay, in Ben Klibrigg, and in other parts of 

 Sutherland. In these cases there appears a gradual transition for some space 

 between the two ; the gneiss first putting on the aspect of micaceous schist, 

 which then passes into a micaceous and highly schistose quartz rock, and 



