GEOLOGY 211 



adjacent parts of Norway. The folding and metamorphism 

 were accomplished during the long Caledonian orogeny which 

 is held to have begun in late Ordovician times. 



These views are applied to the similar Moine and Dalradian 

 groups of the Scottish Highlands. Both these formations are 

 regarded as complexes of rocks of different ages, the Moine being 

 composed mainly of Torridonian, Cambrian, and Lewisian in- 

 liers welded together by extreme metamorphism, the Dalradian 

 mainly of Cambro-Silurian sediments. In support of the latter 

 contention, an impressive petrographical and stratigraphical 

 comparison is drawn between the Dalradian and the Ordovician- 

 Silurian rocks of the Southern Uplands. The analogies be- 

 tween the Scottish region and that of Central Scandinavia are 

 thoroughly exploited in aid of the view that the Scottish schist 

 groups, like the Scandinavian, are not of Pre-Cambrian age, 

 and have suffered but one period of folding and metamorphism, 

 namely the Caledonian. 



Structural conditions are also similar. Fan anticlines are 

 pressed up in the central portions of synclinal depressions con- 

 sisting of Cambro-Silurian strata pinched in hollows of the 

 Archaean basement, and squeezed out laterally with the forma- 

 tion of inwardly-dipping recumbent folds and thrusts. 



Another important point brought out in this paper is the 

 scepticism of present-day Scandinavian geologists as to the 

 enormous distances (80 to ico miles, according to Tornebohm) 

 over which the thrust blocks are alleged to have moved. Frodin 

 reduces the thrust distance in Jemtland to one-tenth of the 

 original figures, thus bringing the Scandinavian thrusts to the 

 same order of size as the Scottish. The details of Frodin's work 

 on Central Scandinavian highland geology, referred to above, 

 are contained in a long and important paper entitled " Uber die 

 Geologic der Zentralschwedischen Hochgebirge " {Bull. Geol. 

 Inst. Upsala, 18, 1922, 57-197)- 



The Scandinavian " mountain-problem " is treated by O. 

 Holtedahl [Quart. Journ. Geol. Soc, 76, pt. 4, 1920, 1-25) for 

 North and South Norway on much the same lines as Frodin for 

 Central Sweden. Few Norwegian investigators, apparently, 

 have ever believed in the pre-Cambrian age of the thrust blocks 

 that overlie rocks of Lower Cambrian age in that country. 

 Materials of different ages make up the thrust blocks, the 

 differences depending on the inclinations of the thrust planes 

 and the depths to which they have reached. Only rarely has 

 their material been brought up from below the pre-Cambrian 

 peneplane surface. Holtedahl gives some illuminating serial 

 sections, showing the progress of events in the Caledonian 

 folding in Finmarken (N. Norway) and the Randsfjord region 

 (S. Norway). 



