64 SECTIONAL ADDRESSES. 



The Jamtland Cambrian rests upon crystalline rocks, mainly granite 

 or porphyry. To the south of the province, however, there is a great 

 development of a fl t-lpng Precambrian formation (sandstone, &c.) called 

 Sparagmite, which is of later date than the granite and porphyry and 

 is often compared with the Torridonian of the Scottish North-west 

 Highlands. 



The Cambro-Silurian succession of the Jamtland foreland is undisturbed 

 in the south-eastern part of its exposure. Gradually, north-westwards, 

 this tranquillity is replaced by isoclinal folding, small-scale thrusting, and 

 intense distributed shearing, unaccompanied by any marked development 

 of metamorphic minerals. Above lies the great Scandinavian thrust- 

 mass or ' nappe,' the cause and origin of all the trouble. 



The contents of this over-riding ' nappe ' are various ; in the main 

 they consist of metamorphosed sediments, which have been somewhat 

 provisionally divided into (1) Precambrian, correlated with Sparagmite, 

 overlain by (2) early Palaeozoic. In both sets of rocks the metamorphic 

 grade increases strongly towards the north-west, but there is good, though 

 not undisputed, evidence that much of the crystallisation of the Pre- 

 cambrian part of the ' nappe ' is of Precambrian date. An important 

 detail, that everybody admits, is the frequent occurrence of recognisable 

 scraps of crushed Precambrian granite and porphyry along the actual 

 thrust. 



The ' nappe ' lies with broad undulations that make it virtually flat 

 over a vast stretch of country. In consequence, erosion has given an 

 extremely sinuous eastern margin to the portion that remains connected 

 with the ' root region ' to the north-west. Moreover, in front of this 

 intricate margin there are great outliers or ' klippes,' the largest of which 

 measures 30 by 10 miles ; while behind there are elongated anticlinal 

 ' windows ' of comparable magnitude, in which we obtain circumscribed 

 exposures of the buried foreland. Altogether we are furnished with a 

 wonderful opportunity for measuring the distance that the mountain 

 region has been driven forward over Baltica. When, in 1888, Tornebohm 

 first propounded his overthrust theory of the Scandinavian Chain, he 

 mentioned sixty miles as a minimum displacement and compared this 

 estimate with the half-mile of overthrusting previously described by 

 himself from Dalsland and with Peach and Home's ten miles from the 

 North-west Highlands of Scotland. In 1896, by which time he had 

 received important help from Hogbom, he was able to demonstrate that 

 the Scandinavian thrusting exceeds eighty miles. One is amazed by the 

 scale of the phenomenon thus elucidated practically single-handed. 

 Tornebohm built upon his own explorations and corrected his own initial 

 mistakes. Jamtland as regards area is comparable with Switzerland, but 

 in Tornebohm's field of inquiry it occupied merely the position of a 

 province. A big man in body and mind, he was faced with a task that 

 required exceptional equipment. Hogbom, writing shortly after Torne- 

 bohm's death in 1911, recalled ' how sometimes his assistants ran away 

 from him because they could not endure the fatigues or follow him when 

 with his great strides he rambled over the mountains.' These words read 

 strangely like a parable, for to-day Scandinavian geologists have turned 

 back to experiment for themselves with all the philosophies of double- 



