Vice- President s Address. 177 



features all others are of subordinate importance. The two 

 great troughs are belts of depression in the continental 

 plateau itself. The northern one is of extreme antiquity — 

 it is older, at all events, than the Cambro-Silurian period. 

 Even at that distant date, its southern limits were marked 

 out by ridges of Archaean rock, which, as I have said, seem 

 to have formed islands in what is now Central Europe. 

 It was probably always the shallower depression of the 

 two, for we have evidence to show that a^ain and ajrain. 

 in Mesozoic and later times, the sea that overtlowed what 

 are now the central lowlands of Europe, was of less con- 

 siderable depth than that which occupied the Mediterranean 

 trough. 



If we turn to ]N"orth America, we find similar reason to 

 conclude with Professor Dana that the general topography of 

 that region had likewise been foreshadowed as far back as the 

 beginning of the Palaeozoic era. Dana tells us that even then 

 the formation of its chief mountain-chains had been com- 

 menced, and its great intermediate basins were already defined. 

 The oldest lands of North America were built up, as in 

 Europe, of Azoic rocks, and were grouped chiefly in the north. 

 Archaean masses extend over an enormous region, from the 

 shores of the Arctic Ocean down to the great lake country, 

 and they are seen likewise in Greenland and many of the 

 Arctic islands. They appear also in the long mountain- 

 chains that run parallel with the coast-lines of the continent. 

 In a word, the present distribution of the Archaean rocks, and 

 their relation to the overlying strata, leads to the belief 

 that in North America, just as in Europe, they form the 

 foundation-stones of that continent, and stretch continuouslv 

 throuo'hout its whole extent. 



We know comparatively little of the geology of the other 

 great land-masses of the globe, but from such evidence as we 

 have, there is reason to believe that these in their general 

 structure have much the same story to tell as Europe and 

 North America. In South America, Archaean rocks extend 

 over vast areas in the east and north-east, and reappear in 

 the lofty mountain -chains of the Pacific border. They have 

 been recognised also in various parts of Africa, alike in the 



