74 SECTIONAL ADDRESSES. 



waters covered mucli of tlie foreland, for instance the greater part of 

 Belgium, England and Ireland, where it encouraged the growth of 

 Carboniferous Limestone. At the same time, the interior Hercynian 

 zone, lying to the south, showed signs of mountain development, and 

 uplifted portions furnished sand and mud to the contiguous sea. The 

 contrast of the limestone facies of the foreland and the mud facies of the 

 mountain belt is very reminiscent of what one has already described in 

 connection with the Ordovician rocks of Canada. It is almost certain that 

 the northward travel of the Hercynian mud was checked by a successor 

 of the Condroz Slope leading down from the shallow waters of the sub- 

 merged foreland to the foredeep of the growing chain. 



Without attempting to sketch this history even in outline, let us pass 

 on to Millstone Grit times, when a slackening in the general subsidence 

 of the foreland allowed deltas from the persistent northern continent to 

 join with others from the growing southern mountains. They met upon 

 the site of the erstwhile Carboniferous Limestone Sea and thereafter 

 placed Scotland in frequent communication with contemporary land 

 regions in France and Germany. Just at this critical time, as Kidston 

 and Traquair have shown, the land flora and estuarine fish fauna of Scotland 

 underwent a remarkably sudden alteration ; whereas the fauna of the 

 open sea showed no corresponding change. The new flora, that all at 

 once appeared in Scotland, is one that has been demonstrated by Potoni6 

 and others to have arisen in a normal gradual fashion on the deltas 

 fronting the nascent Hercynian Mountains ; and I attribute its abrupt 

 introduction into Scotland to migration across the confluent southern 

 and northern deltas of the Millstone Grit. The contemporaneous renova- 

 tion of the estuarine fish fauna of Scotland can also be explained by the 

 meeting of the deltas, since this event made Scottish rivers tributary to 

 the general drainage system of western Europe. Hitherto these rivers 

 had enjoyed biological isolation through emptying directly into the 

 CarboniJFerous Limestone Sea. Henceforward their doors stood open to 

 migration from the South. 



There is another aspect of the deltaic apron of the Hercynian Mountains 

 which used to appeal insistently to the imagination of Marcel Bertrand. 

 This deltaic accumulation gathered in the frontal depression of the growing 

 Hercynian Chain, and to-day it furnishes the greatest belt of coalfields in 

 the whole of Europe. We know it in Upper Silesia and again in the Ruhr, 

 Belgium, North-east France, Dover, Somerset, and South Wales. It is 

 also represented in Ireland, but, as everyone knows, widespread denudation 

 of Coal Measures is one of the admitted injustices that have been dealt 

 out to our sister island. 



Let us now turn to a very interesting feature of tectonics, of which 

 there are two independent illustrations along the course of the Hercynian 

 Mountains of western Europe : I refer to the crossing of mountain chains. 

 In Upper Silesia the front of the Hercynian Chain emerges from beneath 

 the Carpathians, while in the British Isles it obliterates for the time being 

 the south-westward continuation of the Caledonian Chain. 



Where the Carpathians and Alps have trespassed upon the domain of 

 the Hercynian Mountains the latter had already been buried beneath an 

 unconformable cover of Mesozoic and Tertiary marine sediments. This 



