part 4] THE SCANDINAVIAN ' MOUNTAIN PROBLEM.' 401 



gabbro and the granite at the time when the conglomerates were 

 formed, were cooled, solid masses, exposed at the surface. There 

 are also other features general^ met with in different districts of 

 the eastern zone of deformation, which indicate that the igneons 

 masses were to a considerable extent moved as solid masses. So 

 we may find very commonlv, at the base of the thrust igneous 

 masses, mylonitic zones implying a dynamical crushing of solid 

 material. This might by some perhaps be taken as a proof that 

 the igneous rocks in question, despite other facts, must be con- 

 sidered as of ancient, probably Archaean, age, and not as Caledonian 

 intrusions ; but this is certainly not the case. 



There is no doubt whatever that the crust-movements which 

 Ave call ' the Caledonian deformation ' have lasted for a very long 

 time. As to this question, I might refer to my recent paper 

 on u Palseogeography & Diastrophism in the Atlantic-Arctic 

 liegion during Palaeozoic Time.' 1 It is, further, only natural to 

 assume that the time during which the igneous masses moved or 

 were moved, under constant pressure, from the central zone of 

 deformation to the border-belt 30 to 40 miles away to the south- 

 east, may have been of considerable length. 



We do not, therefore, strain our imagination in assuming that 

 more or less of the sheet-like peripheral part of the igneous body 

 was present as a cooled and solid mass, while in the central 

 synclinal zone of deformation, where the roots of the body have to 

 be sought, magmatic masses still poured forth. As to the relation 

 between the conglomerates of the post-Ordovician Sparagmite Series 

 just mentioned and the overlying gabbro and granite, it is evident, 

 if we assume a considerable lapse of time for the deformation, that 

 an igneous mass, the intrusion of which took place in the earlier 

 part of the period of crust-movement, may very well have been 

 exposed and weathered into conglomeratic material before the 

 deformation, the last effort of which was the thrusting of the 

 gabbro and granite above the conglomerates, was finally at an end. 

 This more or less ' dead ' state of the igneous masses when they 

 reached far towards the south-east in many cases explains the fact 

 that veins and dykes cutting the underlying sediments are missing- 

 here (while they are found in the more central zone of deformation), 

 a fact previously considered as excluding the hypothesis of the 

 later, Caledonian origin of the granites and gneisses. 



An important theoretical question to be taken into consideration 

 by future research is the possibility of the intrusions being more or 

 less a cause of the movement of the bordering sedimentary masses. 

 It seems probable enough that an igneous body, through a combined 

 regional and contact-metamorphism, might physically become very 

 closely attached to the surrounding mass. As has been stated, we 

 find commonly, as in Finmarken, a wholly crystalline contact- zone. 

 When the igneous mass became consolidated and, through the 

 pressure from magmatic masses, still coming forth from the central 



1 Amer. Jcrarn. Sci. ser. 4, vol. xlix (1920), especially pp. 9-10. 



