402 PROF. OLAF HOLTEDAHL OX THE [vol. lxxvi, 



part of the zone of deformation, was pushed towards the south- 

 east and thus a thrust-plane had to be developed, this jjlane might 

 in some cases be developed far below the igneous body, in the less 

 altered sediments, and the whole overlying mass moved as a unit 

 (compare fig. 4, p. 396). 



The future study of the detailed mechanics of the igneous 

 masses in the eastern part of the Scandinavian mountain-zone, 

 these masses being considered not as Archaean tracts of rock, but 

 as parts of Caledonian magmatic bodies, will certainly be one of 

 considerable general interest. 



Discussion. 



Sir Jethro Teall said that the paper was of great interest to 

 him. It had been his good fortune to be associated with the work 

 of the late Prof. Lapworth in the North- West of Scotland in 1883, 

 and afterwards with that of the Geological Survey. It was obvious 

 that there were resemblances and differences between the two 

 regions. Both Lapworth and the Survey bad proved that in 

 certain places undoubted Archaean rocks had been superposed on 

 fossiliferous Lower Palaeozoic rocks by powerful earth-movements; 

 but the question of the age and date of the rnetamorphisni of the 

 crystalline schists of sedimentary origin, which occupied the same 

 position in other parts of the North- West, had not as yet been 

 definitely settled, although there Avas evidence pointing to the 

 conclusion that the metamorphism at least was of post- Cambrian 

 date. Certain igneous rocks of peculiar composition resembling 

 rocks that had been intruded into Cambrian strata — the Canisp 

 porphyrite, for example — had been incorporated as part and parcel 

 of the Moine Schist Series. 



The Author maintained that certain crystalline schists over- 

 lying the thrusts in Scandinavia were of post-Cambrian age. He 

 (the speaker) would welcome such a conclusion, but would like to 

 study the paper very carefully before expressing an opinion on this 

 point. If clearly established, it would have an important bearing 

 on Scottish geolog} r . He had a perfectly open mind as to the age 

 of the metamorphosed sediments and associated igneous rocks, also 

 metamorphosed, which occupied so large a part of the Scottish 

 Highlands. 



Mr. Bernard Smith commented upon the Author's statement 

 that the movements giving - rise to thrusts had been from the 

 north and the north-west. In studying phenomena related to 

 Caledonian and later movements in North Wales, the speaker 

 and his colleague (Mr. C. B. Wedd) had been driven to the 

 conclusion that certain structures apparently caused by move- 

 ments from a northerly or north-westerly direction were really 

 due to deep-seated movements of underlying rocks in the opposite 

 direction. The deep-seated more rigid rocks had moved forward 

 relatively first, while the younger less rigid rock had lagged behind. 



