394 W. S. Hudleston — First Impressions of Assy nt. 



same beds are again passed over. This is admirably shown by the 

 different bedded igneous rocks, which now reappear in reversed 

 order. With such evidences of rolling over and instability of dip, 

 one is naturally led to question the value of the apparent super- 

 jDOsition of the Quartzite to the Dolomite, which is seen below, though 

 it would be going too far to say that the evidence of this section in 

 favour of the existence of an Upper Quartzite is altogether to be 

 discai-ded in favour of the notion of a reversed fault at the junction, 

 This is the only place seen by me where there could be any grounds 

 for requiring the existence of an Upper Quartzite. 



In the great mountains of the eastern range there really seems 

 very little evidence of the true stratigraphical relations of the vast 

 beds of Quartzite to the fragments of Dolomite, which are pitched 

 about in all directions on some of the lower grounds. As far as one 

 can judge from such a chopped-up district, it would seem that there 

 is a very considerable convergence of dips towards Loch Maolach 

 Corrie, and thus that the Quartzite, on the east of the large area of 

 dolomitic limestone thereabouts, underlies the limestone just as it does 

 on the west. It follows, therefore, that the Quartzite of Breabag, 

 etc., is a mere repetition, possibly with some thickening, of the 

 regularly bedded Quartzite of the western range usually known as 

 the Lower Quartzite. 



But, quitting individual sections, there remains the general im- 

 pression derived from an inspection of geological majDS, and based 

 upon the presumed continuance of an easterly dtp in all the beds, 

 that those quartzites occurring to the east of the dolomite escarpment 

 must be Upper Quartzite, unless the contrary can be shown. It is 

 just possible, however, that the explanation which fits so well for 

 the Quartzite of Breabag may, with modification, apply along the 

 whole line. This supposes a roll up of the Lower or western 

 Quartzite in a series of convolutions to the east of the Dolomite 

 which has been assumed to pass beneath it. Much stress has 

 been laid upon the presumed lithological differences between the 

 Lower and the alleged Upper Quartzite. As far as I could see, 

 these differences amount to very little, their leading features, even 

 to the purplish colour of some of the beds, appearing very similar. 



2. What is the nature and geological position of the " Logan " roch ? 

 — This mystei'ious rock has had so many aliases that its individuality, 

 as identified by various writers, runs some risk of being lost. Prof. 

 Heddle has given an excellent summary of the different views 

 respecting it,^ and in a paper read before the Eoyal Society of 

 Edinburgh, on the 17th July last, he assigns the following sequence 

 to the rocks of the North-west Highlands : — Torridon Conglomerates, 

 Lower Quartzite, Dolomite Series, " Logan " rock, Upper Quartzite, 

 Upper Gneiss. 



It may well happen that in the long range from Whiten Head 



to the Sound of Sleat more than one class of rock has been 



enumerated under this head. At present we are more especially 



coiicerned with the Assynt district, though the term "Logan" 



^ Mineralogical Magazine, No. 22, p. 43 et seq. 



