68 STRATIGEAPHICAL GEOLOGY 



there is a conglomerate, the pebbles in which are chiefly of quartz- 

 porphyry and orange-coloured quartzite. The mass of the formation 

 consists of brownish-red or chocolate-coloured felspathic sandstones, 

 in which false-bedding, ripple-marks, and desiccation-cracks are 

 frequently observable. In the higher part thin layers of red shale 

 occur, and there are also intercalated sheets of diabasic lava, some 

 being intrusive sills and others extruded lava-flows which are 

 sometimes amygdaloidal. 



In Scandinavia these Jotnian and Sparagmite sandstones rest 

 nearly everywhere on the rocks of the Protarchsean complex, and 

 the unconformity between them is as striking and profound as 

 that between the Torridonian and Hebridean of Scotland. In the 

 latter country, as stated on p. 39, there is evidence of an inter- 

 mediate formation having existed. In Scandinavia remnants of 

 this (the Jatulian) still exist, but if it ever extended far toward 

 the north it was destroyed before the formation of the Jotnian. 



In the western metamorphosed tract the place of the Jotnian 

 sandstones seems to be taken by the Are schists ; these are mainly 

 quartzose flags and gneissic schists, including white mica-schists 

 and brown garnetiferous schists. ^ Hogbom remarks that petro- 

 graphically and tectonically the Are schists very much resemble 

 the Moine schists of Scotland. Both he and Tornebohm believe 

 that they have originated from the Sparagmite sandstones, the 

 latter becoming " transformed to mylonites, sericite schists, and 

 white mica-schists within the western thrust areas and the crystal- 

 Unity increasing from east to west." There is, however, a greater 

 petrological difference between them than can be accounted for in 

 this way, and there " must also have existed a primary difference 

 between the eastern sparagmites and the western schists, a change 

 of facies characterised partly by the entrance of basic igneous rocks 

 into the western series, partly by the substitution of argillaceous 

 and slaty sediments for the gritty sparagmites and conglomerates. 

 The basic rocks just mentioned, which probably are to a great 

 extent tufaceous (i.e. altered tuffs), repeatedly alternate with these 

 argillaceous beds. Generally speaking, one can say that this 

 change of facies goes on slowly from the east or south-east to the 

 west or north-west." 



REFERENCES 



1 Bonney in Building of the British Isles, by Jukes-Browne. Third edition, 

 p. 21. (Stanford, 1911.) 



2 " Report on Geology of North- West Highlands," Quart. Journ. Geol. Soc. 

 vol. xliv. p. 378 (1888). 



3 See " The Geological Structure of the North- West Highlands of 

 Scotland," Mem. Geol. Survey, 1907, p. 192, etc. 



