66 SECTIONAL ADDRESSES. 



nearly to North America than to the rest of Britain. This fact was 

 recognised in the fifties of last century by Salter when he described C. W. 

 Peach's collections from the Durness Limestone. He had already had the 

 good fortune of familiarising himself at first hand with Canadian material. 

 There is no chance of unravelling the original relations of the American 

 and British facies of the early Palseozoic in Scotland, or even in Norway, 

 where Holtedahl has recently recognised the American facies of the early 

 Ordovician on the Island of Smolen, west of Trondhjem. Let us 

 therefore set sail for America. 



The Atlantic seaboard of North America,' southwards from New- 

 foundland, is constituted of Palaeozoic mountains, partially concealed, it 

 is true, from New York to the Gulf of Mexico beneath a coastal spread of 

 Cretaceous and Tertiary rocks. American geologists call their ancient 

 mountains the Appalachian System. To European eyes they appear as 

 a complex of two systems, rather than as a single system ; but for the 

 moment we may let this pass. Beyond the Appalachian Mountains lies 

 an enormous interior region, the Laurentia of Suess, that, like Baltica, 

 has remained unaffected by folding since late Precambrian days. 

 Laurentia, again like Baltica, has two main elements ; a vast exposure 

 of Precambrian rocks, the Canadian Shield, recalls at once the Baltic 

 Shield ; while the Great Plains, with their cover of Cambrian and later 

 formations, correspond with the Russian Platform, and are bounded on 

 the south-west by a Mesozoic-Tertiary cordillera. The comparison^ may 

 be pushed to matters of detail, for a narrow offshoot of flat Palseozoic 

 rocks extends from the Great Plains along the St. Lawrence Lowlands 

 to separate the Canadian Shield from the Appalachians, just as a strip of 

 flat Palseozoic rocks runs up through Jamtland to separate the Baltic 

 Shield from the Scandinavian portion of the Caledonian Chain. 



With so many points of comparison, it is not surprising to find that we 

 can go farther still. The age and relations of the portion of the Appalachian 

 complex, which borders the St. Lawrence Lowlands, justifies our grouping 

 it with the Caledonian System. It was Marcel Bertrand who, in 1887, 

 saw that the Appalachian Mountains, as a whole, could be partitioned among 

 the two great Palaeozoic systems that, on our side of the water, meet in 

 South Wales. In Newfoundland, Canada and northern New England the 

 Appalachian Mountains belong to the Caledonian System, in the sense 

 that their main movements were completed before the close of the 

 Devonian period. We may quote from Young in his Geology and Economic 

 Minerals of Canada published by the Canadian Geological Survey in 1926 : 

 ' Before the close of the Devonian period,' he says, ' the Appalachian and 

 Acadian regions were uplifted and the strata folded and faulted, and 



1 Last year I had the privilege of sharing, with my friend Collet, in the Princeton 

 Summer School excursion organised by Field, and anything I have to say on American 

 Geology is directly or indirectly the result of this experience. 



2 When in Nature, November 5, 1927, 1 developed the idea that ' the North 

 American Continent is, broadly speaking, a magnified mirror image of much of 

 Europe,' I was unaware how closely I was following 0. Holtedahl in ' Some points of 

 Structural Resemblance between Spitsbergen and Great Britain, and between Europe 

 and North America,' Aihandl. Norske Videnskeps-Akad., Oslo, I, 1925, No. 4. 



