326 ROLLIN T. CHAMBERLIN 



In the Yukon region of Alaska, according to Brooks and Kindle, 

 it seems probable that one of the recurrent epochs of crustal dis- 

 turbances took place in early Devonian or late Silurian times, for 

 all the rocks laid down before this period appear to fall into the 

 metamorphic class, though they have suffered a varying amount of 

 alteration. Granitic intrusions are associated with this folding 

 and it is probable that this epoch was closed by an uplift followed 

 by erosion.^ 



In northeast Greenland, what appears to be an orogenic move- 

 ment at the close of the Silurian has been recognized and described 

 by Nathorst as follows: 



The Silurian strata, as we have seen, are folded and compressed and partly 

 metamorphosed. If this bears any relation to the formation of a mountain 

 range, the folding took place before the deposition of the Devonian strata, for 

 the latter show only a relatively slight amount of disturbance. Otherwise it 

 must be surmised that the folding was the result of a depression of the Silu- 

 rian strata along a fault at their eastern border, or perhaps between such a fault 

 and another which can be imagined as passing west of the present boundary 

 of the Archean.2 



This folding in northeast Greenland parallels and may perhaps be 

 related to the great Caledonian folding of Scotland and Scandinavia. 

 In Europe the close of the Silurian was a time of much greater 

 disturbance. Flexing and faulting of the crust at this time devel- 

 oped a chain of stupendous mountains in northwestern Europe. 

 The present stumps of these great mountains run throughout the 

 length of Scandinavia; reappear in the northwest highlands of 

 Scotland, and extend onward into Ireland, Wales, and England. 

 Evidences of these ancient mountains are to be recognized as far 

 south as Devonshire. To this chain Suess has applied the name 

 Caledonian, recognizing it as one of the greatest ranges of the past.^ 

 Both in Scandinavia'' and in the Scottish Highlands^ the formation 



' A. H. Brooks and E. M. Kindle, "Paleozoic and Associated Rocks of the Upper 

 Yukon, Alaska," Bull Geol. Soc. Am., XIX (1908), 312-13. 



^ A. G. Nathorst, cited by Willis, op. cit., p. 341. 



3 Eduard Suess, The Face of the Earth, Sollas trans., II (1906), 82-86; III (1908), 

 386-99. 



4 A. E. Tornebohm, "Grunddragen af det Centrala Skandinaviens Bergbyggnad," 

 K. Svenska Vetensk Akad. Handl., XXVIII (1896), 212. 



s B. N. Peach, J. Home, and others, "The Geological Structure of the Northwest 

 Highlands of Scotland," Me^n. Geol. Survey of Great Britain (1907), 463-594. 



