C— GEOLOGY. 71 



of their fronts (syntaxis) near Valenciennes on the Franco-Belgian border. 

 The eastern arc he called Variscan, the western Armorican. The names 

 are based on the Latin for the Bavarian town of Hof, Curia Variscorum, 

 and for the French province of Brittany, Armorica. The meeting of the 

 two arcs near Valenciennes is closely comparable with the meeting of the 

 Carpathians and Alps near Vienna. 



The date of the Armorican and Variscan folding varies somewhat 

 according to locality, but lies either within, or at latest shortly after the 

 close of, the Carboniferous. Bertrand, publishing the same year as 

 Suess, classed these mountains on a purely age basis, as part of his 

 Hercynian System (called after the Harz). Unfortunately Bertrand's 

 name Hercynian was preoccupied ; but I propose to use it in his sense in 

 the present description. 



The Hercynian Mountains of Western Europe are on the whole less 

 continuously exposed than the Caledonian. The eastern front of the 

 Variscan Arc is traceable at the foot of the Sudetes bordering the Upper 

 Silesian coalfield that lies north of the Carpathians. From this point it 

 is lost sight of for a long stretch, but reappears, from beneath the North 

 German Plain, in the Ruhr coalfield of Westphalia. Westwards its 

 continuation passes along the Belgian coalfield, where it is very well 

 known, partly in surface exposures, partly in mining operations. Across 

 the French border it joins the front of the Armorican Arc which has been 

 traced, mostly underground, as far as the Pas de Calais coalfield. It is 

 still buried south of Dover, but comes to the surface again in the Somerset 

 and South Welsh coalfields, and is clearly exposed across the south of 

 Ireland. 



The course of this Hercynian front, where hidden, can often be inferred 

 from trend lines in some neighbouring exposure of the interior. The main 

 gap in the evidence, as a whole, is due to the Mesozoic and Tertiary cover 

 that reaches from near Bristol, by the Isle of Wight, the Channel and the 

 Paris Basin, onwards to the Juras. There is, however, no doubt that the 

 Palaeozoic and older exposures of South Wales, Devonshire, Brittany and 

 the Central Plateau, on the one side, belong to the same mountain system 

 as those of the Ardennes, the Vosges and the Black Forest on the other. 

 In between the mountains are buried, not discontinuous. 



The interior of the European Hercynian Mountains developed earlier 

 than their northern periphery. At the close of Dinantian times, that is 

 a little earlier than our Millstone Grit, much of the interior region yielded 

 freely, for the last time, to mountain deformation ; whereas in the peri- 

 pheral belt the main folding took place at some date towards the end of 

 Coal Measure times. The contrast between the two portions of the chain 

 is particularly striking if we compare the Saar Coalfield, on the south side 

 of the Ardennes, with that of Belgium, on the north. The Coal Measures 

 at Saar belong to the Hercynian interior region and are violently uncon- 

 formable to folded Devonian ; whereas those of Belgium complete a 

 conformable sequence extending up from the Devonian, and have shared 

 in the corrugation and overthrusting of the latter. This condition of 

 affairs reminds us of the two stages in the Caledonian folding of southern 

 Scotland, where the date of folding depends upon position with reference 

 to the Girvan-Edinburgh Une. 



