C— GEOLOGY. 75 



relation is particularly clear in certain anticlinal re-exposures of the old 

 mountains furnished by the Alpine massifs of the Aar and Mt. Blanc. 

 Where the Hercynian front crosses the Caledonian Chain in Ireland the 

 new mountains, at the present level of denudation, consist of Devonian 

 and Carboniferous sediments ; and the old mountains can only be seen 

 to the north of them, uncovered by denudation along gentle anticlines 

 developed in the foreland. In South Wales the crossing of the Caledonian 

 Chain by the Hercynian does not proceed very far, for the strike of the 

 older structures veers round into approximate parallelism with that of 

 the modern chain at the line of mutual contact. It is not known whether 

 this curvature is original or superinduced. 



We may recall that the crossing of the two Palaeozoic mountain chains 

 of south-west Britain is one of the topics dealt with by De la Beche in 

 1846, in the first volume of memoirs published by our Geological Survey. 

 ' This,' says Suess in his Anilitz der Erde, ' I cannot mention without an 

 expression of deep gratitude to the author, now long since dead, since it 

 exercised many years ago a decisive influence on my own views as to the 

 structure of great mountain ranges.' If I were to continue the quotation 

 it would lead on to the subject of granite intrusions in relation to folded 

 mountains — but space absolutely forbids touching upon this side of the 

 subject. 



For the last time let us take boat across the Atlantic, there to visit 

 the American representative of the Hercynian System. We know exactly 

 where to go. From New York southwards, the north-west front of the 

 Appalachian complex consists of folded and often overthrust Palaeozoic 

 eediments that extend upwards into Coal Measures. This belt it was 

 that gave the brothers Rogers material for their ever-famous address 

 delivered in 1842 before the American Association of Geologists. We 

 need only recall how the two brothers demonstrated to a spell-bound 

 audience the asymmetry, isoclinal packing, steep thrusts and general 

 travel of the Appalachians ; and how their work was immediately recog- 

 nised as of international importance. 



It has been said above that Coal Measures are affected by the folding 

 of the portion of the Appalachians now under consideration. The last 

 great movement seems to have been in the early Permian. Accordingly 

 Marcel Bertrand, in 1887, placed this frontal Pennsylvanian belt of the 

 Appalachian Complex in his Hercynian System. 



The most interesting peculiarity of the Hercynian System in America 

 is ite penetration to Laurentia, to the north-west foreland of the Caledonian 

 System. The crossing of the chains, begun in the British Isles, is com- 

 pleted in New England. The actual front of the Hercynian Chain cannot 

 be mapped with precision in the American part of the zone of crossing, 

 because the critical district has been largely denuded of its Carboniferous 

 rocks. At the same time important Carboniferous outliers do occur in 

 the southern States of New England and are strongly folded ; whereas, it 

 will be remembered, the Carboniferous spreads of the maritime provinces 

 of Canada are toleralaly undisturbed. The best known of the New England 

 outcrops crosses Rhode Island, and its prevailing rocks are conglomerate, 

 arkose and slate. There are also a few beds of graphitic coal, the Upper 



