72 SECTIONAL ADDRESSES. 



A further complication is encountered in the Variscan Arc, if we look 

 behind the commencement of Carboniferous time. We then find that 

 the frontal line of the Variscan Arc occupies a median position as regards 

 a local Caledonian arc that is recognisable in much of Belgium and southern 

 Germany. Actually within the breadth of this early arc there is a great 

 unconformity between Silurian and Devonian ; whereas in the concavity 

 to the south there is conformity, as exemplified in Bohemia. The limits 

 of the Belgio-German Caledonian arc are very imperfectly known. It 

 may, for instance, connect westwards, through Cornwall, with the main 

 Caledonian Chain of Britain and Scandinavia. 



The Franco-Belgio-German coalfield at the northern front of the 

 Hercynian Mountains has long provided a favourite theme among 

 tectonists. As far back as 1832 Dumont published a map with sections 

 elucidating the isoclinal folding, but not the thrusting, of the Li^ge district 

 in Belgium. He emphasised that ' one cannot employ dip to establish 

 the relative age of primordial rocks.' He understood the position so 

 clearly that he defined ' basins ' and ' saddles,' not by the inclination of 

 their marginal exposures, but by the downward or upward direction of 

 their convexities. Having satisfied himself of the basin arrangement of 

 the Coal Measures of his district, he worked outwards into the older rocks, 

 and made substantial progress in zoning what we now call the Lower 

 Carboniferous and Devonian. The referees who crowned his memoir 

 for the Brussels Academy remarked that his work demonstrated violent 

 folding with reversal, and that it suggested the effect that would follow 

 from ' the gliding of a section of the earth's crust down an inclined plane 

 with resultant lateral pressure ' upon the country standing in the way. 

 I do not think that any other country can boast of so advanced a tectonic 

 study of such early date. 



In 1849 H. D. Rogers was able to point out that the district presented 

 ' precisely analogous features ... [to those] which had been observed 

 [by himself] in the Appalachians.' In 1877 Cornet and Briart, and in 

 1879 Gosselet, announced large-scale over-thrusting, the first of the kind 

 to be recognised in European Palaeozoic chains. Peach and Home, it 

 will be remembered, published on Scotland in 1884, and Tornebohm on 

 Scandinavia in 1888. 



A peculiar interest attaches to Gosselet's paper, for Bertrand in 1884 

 made it the basis of his famous comparison between Belgium and the 

 Alps, and derived from it conceptions of much more extensive thrusting 

 in the latter region than had hitherto been imagined. Bertrand's boldness 

 has since been justified by Schardt's 1893 interpretation of the Prealps 

 and all the marvellous consequences that have flowed therefrom. 



I do not propose to go into detail regarding the marginal northward 

 thrusting of the Hercynian Chain. It is of the same type, though not, in 

 my opinion, so extensive, as the Caledonian thrusting of Jamtland, 

 Scotland and Canada. Of recent years much the most delightful addition 

 to our knowledge of the ground has been afforded by Fourmarier's 1905 

 interpretation of the Window of Theux, south of Lifege. The frame of 

 the ' window ' consists entirely of Cambrian and Lower Devonian, whereas 

 the * window ' exposure, some eight miles broad, shows, in addition, every 

 group from Middle Devonian to Middle Carboniferous. The boundary of 



