W. H. Rudleston — Flnt Impressions of Assynt. 399 



visiting the junction of what is usually regarded as Upper Gneiss 

 with the Quartzite. This was at the Stack of Grlencoul (about 

 1700 feet), where the Dolomite is absent. No actual contact was 

 observed here, but the direction and amount of dip of the two 

 formations are, as far as I remember, about the same ; and, what is 

 more, there really seems to be a sort of lithological passage between 

 the regular Quartzite and the fine quartzose flags which gradually 

 conduct to the more micaceous beds. I may be wrong, as the spot 

 is very remote, and only accessible after fatigues which rather impair 

 one's powers of observation. 



Conclusion. — -There are several minor points on which I have not 

 touched. One of these is the relation of the Ledbeg Marble to the 

 Dolomite. These marbles are fragmentary masses lying somewhat 

 in the direction of the strike of the Stronchrubie Dolomite, and 

 apparently associated with Quartzite, which is hemmed in between 

 a ridge of " Logan " rock on the west and the so-called porphyry of 

 Loch Borrolan on the east. These marbles effervesce with acid far 

 more readily than do the dolomites, and from this I infer that the 

 carbonate is principally lime. On the other hand, they contain a 

 considerable development of silicates, either serpentine or malacolite 

 — perhaps both. The magnesia in these beds, therefore, may exist 

 in combination with silica rather than with carbonic acid. One can 

 hardly say whether the difference between these two groups is one 

 of origin, or merely superinduced through contact alteration, as was 

 suggested by Nicol. The subject is an interesting one, but requires 

 close attention and a careful examination of numerous specimens. 

 It certainly seems a little far-fetched to go in search of another 

 geological formation, in which to locate these curious and by no 

 means extensive fragments. 



There is another observation which my short trip to Sutherland 

 has induced me to make, viz. that the local strike of beds cannot 

 always be accepted as an indication of the group to which they 

 belong. There has been too much dogmatism on this point. It is 

 quite possible that a prevalent strike exists for cei'tain groups, but 

 the exceptions to the direction of this are so numerous, especially in 

 the more distui'bed districts, that no one should pretend to be guided 

 by the strike alone to any conclusions of importance with reference 

 to the grouping of beds in limited areas. 



It is not without feelings of regret that I cannot see my way to an 

 Upper Quartzite, and if I have been wrong about the position of the 

 " Logan" rock, I still think that this monster will, in most places, 

 have to be dealt with on the basis of a fold over of some of the lower 

 beds. The sequence at Craig-a-Knockan, showing the superposition 

 of the Upper Gneiss, seems to be unshaken. 



There are workers now in the country, skilled in the interpreta- 

 tion of the older rocks. May it be given to them effectually to 

 pierce the mists of Assynt, and to raise the veil which yet hangs 

 over portions of the North-West ! 



