404 SCIENCE PROGRESS 



graptolites belonging to the lower part of the true Silurian, 

 in the eastern series. These fossiliferous beds are held to 

 support the view that the schists of the area are altered Lower 

 Palaeozoic rocks. This, however, is the one conclusion in 

 Scandinavian geology which foreign geologists may be most 

 excused if they hesitate to accept, until further evidence has been 

 published that the fossiliferous beds cannot be younger rocks 

 folded or faulted in among older schists. The solution which 

 Prof. Bonney gave of the same problem in the Lepontine Alps 

 may be applicable to the schists of the Trondhjem district. 



The belief that these schists were all Silurian was, however, 

 naturally adopted at first, because unaltered fossiliferous Lower 

 Palaeozic rocks are found in places beneath wide sheets of schist 

 and gneiss. It therefore appeared necessary to accept the upper 

 beds as the younger in age. But it has been proved that, as in 

 Scotland and the Alps, the superposition of the schists is due to 

 earth movements. And in Scandinavia the overthrusting has 

 taken place on a scale greater than has been established in any 

 other part of the world. 



The development of these views may be seen from the 

 successive explanations of the geology of Areskutan in Jemtland, 

 one of the best known Swedish mountains (4,645 ft.). The lower 

 eastern and western slopes of this mountain consist of the normal 

 Lower Palaeozoic rocks of the eastern facies ; they include the 

 Cambrian alum shales, above which are more shales, and the 

 Pentamerus Limestone of the base of the true Silurian. The 

 whole of the upper part of the mountain consists of crystalline 

 schists of the Seve Group ; they include hornblende schist, mica 

 schist, crystalline limestone, and garnetiferous gneiss. The base 

 of the crystalline schists is a quartzite or quartz-schist, which 

 is in places a conglomerate. " The contact between this quartzite 

 and the Silurian clay rocks I saw laid bare," says Tornebohm,^ 

 " in a small stream that descends from the western side of 

 Areskutan. The dip is here not more than 15° or 20° to the east, 

 and the superposition is very clear. The boundary between 

 both formations stands out very definitely, yet without any 

 marked discordance. Over the quartzite, which is not very 

 thick, follow first hornblende schists, which alternate with mica 

 and quartzitic schists, and include some small layers, only a few 

 inches thick, of white crystalline limestone ; further up come 



^ Tornebohm, Afhmtdl. Sver. Geol. Unders. No. 9, 1873, P. 4i- 



