76 SECTIONAL ADDRESSES. 



Carboniferous age of which is shown by associated plant remains. Though 

 folded, cleaved and cut by granite and pegmatite, the Rhode Island 

 Carboniferous agrees with that of Canada in being unconformable to the 

 Caledonian disturbances. 



Where at last the Hercynian Mountain front steps clear of its Caledonian 

 predecessor, one encounters a sedimentary superposition of facies that is 

 quite unknown in Europe. In Pennsylvania there is an immense con- 

 cordant succession from Cambrian to Carboniferous. In the cores of 

 anticlines we find our Durness (Beekmantown) Limestone, because we 

 stand on the north-west foreland of the Caledonian Chain. In the hearts 

 of synclines we discover Upper Carboniferous Coal Measures (Penn- 

 sylvanian) derived from the waste of the growing Hercynian Mountains, 

 and we tollow Bertrand in our thoughts to South Wales, the Ruhr and 

 Upper Silesia. 



The study that we have made of mountain chains with their folds and 

 their thrusts, which individually may be of the order of 100 miles, involves 

 a recognition of some type of continental drift. Of late years Wegener 

 has developed this idea on a particularly grand scale. He has accounted 

 for many recognised correspondences in the geology of the two sides of 

 the Atlantic by supposing that the ocean has flowed in between the Old 

 World and the New, as the two continental masses, with geological slow- 

 ness, drifted asunder. One cannot help feeling that Wegener may perhaps 

 be telling us the truth. The available evidence is crude and ambiguous ; 

 but it is certainly startling to be confronted on the coasts of Britain and 

 America with what read like complementary renderings of a single theme : 

 the crossing of Caledonian Mountains by Hercynian. 



