Vol. 50.] ANNIVERSARY ADDRESS OP THE PRESIDENT. 9 1 



their original position by the effect of the Moine thrust-plane — that 

 most terrible of all deceivers. The horizontal section from the 

 Knockan Cliffs to the Cromalt Hills is another edition of the same 

 story. It is needless to say that such classical sections as Cnoc an 

 drein, Coniveall, Ben More, and Breabag, with all that wonderful 

 slicing and plication which each exhibits more or less, are dealt with 

 in afashion that leaves no doubt, when once the key has been obtained, 

 as to the true structure of those remarkable localities. The section 

 across Ben More shows at a glance what a large proportion of this 

 mountain-range consists of Archaean gneiss with its characteristic 

 basic dykes. To use, with a slight modification, the words of the 

 Authors, the slice of Archsean rocks, bearing the thin capping of 

 Torridon Sandstone and Cambrian strata which constitute the actual 

 summit, is of large dimensions. Here the Archaean gneiss with its 

 basic dykes is exhibited in a grand cliff about 1500 feet high over- 

 looking Dubh Loch More, whence it sweeps across the lofty peaks 

 separating the Oykel from the Gorm Lochs. Though still recognizable 

 as a part of the old Archsean platform, the rocks are stated to have 

 undergone important changes due to the movements which have 

 affected them. It was these changes which formerly prevented 

 geologists, Nicol in most instances excepted, from recognizing an 

 old friend under such altered circumstances. 



We must now proceed to consider the nature of the metamorphism 

 resulting from these post-Cambrian movements. The Authors observe 

 that with each successive maximum thrust there is a progressive 

 alteration in the displaced materials. For instance, the great slice 

 of Archsean rocks brought forward by the Glencoul Thrust does not 

 present any striking evidence of deformation, except close to the 

 lines of disruption. The alteration of the Archsean rocks is more 

 pronounced above the horizon of the Ben More Thrust in Assynt, 

 but it is in the belt of sheared gneiss and green schist underlying 

 the Moine thrust-plane that we have the most remarkable evidence 

 relating to this kind of metamorphism. 



In the basal conglomerate, or ' Button-stone,' of the Torridon 

 Sandstone the softer pebbles of gneiss and the fragments of the 

 basic Archsean dykes have been crushed, flattened, and elongated in 

 the direction of movement. Indeed, in some cases, they have been 

 drawn out to such an extent as to form thin lenticular bands of 

 micaceous or hornblende-schist flowing round the harder pebbles of 

 quartz-rock. The original gritty matrix has been converted into a 



