Reviews — Thrust Movements in Norway. 131 



interbedded in it are conglomerates essentially composed of gabbroid 

 stones. The problem is to determine the relationship of these 

 conglomerates to some adjacent gabbro mountain masses which owe 

 their present position to thrusting. In an early paper Bjerlykke 

 held that the conglomerate was derived from the gabbro, and was 

 thus the younger formation. In a later communication, however, 

 the contrary opinion is expressed that the gabbro is younger than the 

 " Heifjeldskvarts ", and was intruded between it and the underlying 

 phyllites. Professor Goldschmidt has made a thorough microscopic 

 investigation of these rocks. The massive gabbro is a very characteristic 

 rock composed of very fresh augite, less fresh biotite, and a wholly 

 decomposed plagioclase ; hornblende varieties also occur. The pebbles 

 of the conglomerate exhibit all the varieties of the massive mountain 

 gabbro, from which they are clearly derived. Thus the " Haif- 

 jeldskvarts" cannot be older than the mountain -building movements, 

 since these conglomerates were laid down after the gabbro masses 

 had reached their present position. Again, the conglomerate can be 

 followed to places where it is overlaid by the gabbro and has been 

 strongly pressed, often almost out of recognition. Thus the " Heifjelds- 

 kvarts " cannot be younger than the thrusting movements, seeing it 

 has been metamorphosed during, and as a result of, their evolution. 

 It is not pre-Caledonian ; it is not post-Caledonian ; it is Caledonian 

 — a conclusion of great significance, for it shows that the thrusting 

 took place at the earth's surface, a conglomerate being laid down 

 during the process. The gabbro was eroded in front, whilst it was 

 being pushed forward from behind. 



The second tract examined lies between Valdres and Hemsedal. 

 Here we have a similar type of structure, only the Ordovician 

 phyllites are overlaid by thrust masses of granite instead of gabbro. 

 In the south of the district the conglomerate beds are seen overlying 

 the granite as a normal basal deposit, with no evidences of pressure 

 action. In the north, on the other hand, the conglomerate has been 

 overridden by the granite, and its pebbles have been pressed and 

 drawn out by the movement. Here also the derivation of much of 

 the conglomerate from the granite which now overlies it is established. 



Thus the investigations in both of these districts lead to the 

 conclusion that the sedimentation of the " Haif jeldskvarts " took 

 place whilst the great eruptive masses were being driven forward, 

 and with deposition of material from the erosion of the selfsame 

 masses. By the continuance of the thrusting movements the 

 sediments were covered and metamorphosed. On this interpretation, 

 and in opposition to the orthodox view that the great thrust move- 

 ments have obtained at a considerable depth, it must be admitted 

 that great mass-thrusting can take place "in daylight" at the 

 surface, so that a mass can be driven forward and be subject to 

 erosion at one and the same time, in such a way as to ride over its 

 own debris. After mentioning the great amount of work which yet 

 remains to be done before all the problems of the " Heif jeldskvarts " 

 can be solved, and the flood of light which a full understanding of 

 this series must throw not only on the formation of the Norwegian 

 mountains but on the general principles of tectonic geology, it is 



