part 4] SCANDINAVIAN ' MOUNTAIN PROBLEM.' 403 



He enquired whether it could be shown that the apparent move- 

 ments from the north and the west, producing the thrusts in 

 Scandinavia, were consequent upon an under-drive of the pre- 

 Cambrian rocks towards the sea, inducing a lagging and piling-up 

 of the overlying Cambro- Silurian strata. 



Mr. E. D. Nicholson remarked that it had been stated by- 

 some writers, more especially the late James Geikie, that the 

 amount of thrust in the Scandinavian ranges is from 70 to 

 80 miles. He asked what was the Author's opinion as to the 

 extent of the thrust. 



Mr. H. W. Monckton expressed his great interest in the paper. 

 He had for many years followed the development of the mountain 

 problem in Scandinavia, more especially with regard to the 

 Author's southern district, with which he was personally acquainted. 

 There was a double question as to the peculiar gneiss-like masses 

 which form some of the highest ground — whether their position 

 was due to overthrusts, and what was their original geological 

 age ? For some time it was believed that they had been derived 

 from the Archsean ; but the Author, while adopting the theory of 

 overthrust, considered the overthrust masses to be newer than the 

 Archaean. The speaker thought that the Author had probably 

 arrived at the true solution. 



The Author strongly emphasized that it was not possible, in 

 a short paper, to go into detail as to all the facts pointing to a 

 younger age of the metamorphosed sedimentary rocks in the 

 various districts that had now been studied. In addition to 

 what was stated in the paper, he would point out that in the 

 Jotunheimen district metamorphosed sedimentary beds lying 

 above less altered ones quite certainly were equivalents of what 

 is called the ' Younger Sparagmite of Valdres,' which was of 

 post-Ordovician but pre-Devonian age. As to the amount of 

 movement, that of the sedimentary masses was probably not, 

 in his opinion, in the southern part of the ' Sparagmite area ' 

 (for example) more than 10 to 20 miles ; while the movement 

 of the igneous rocks in the mountain-zone commonly might be 

 much greater, corresponding to the distance between the eastern 

 border of the igneous masses of the metamorphic cover and the 

 central zone of deformation where the masses had poured forth. 



