418 LAKE SUPERIOR. 



We have in other instances, ridges of mountain chains intersecting 

 the plains and forming prominent walls in various directions across 

 the more level country. We have again isolated peaks rising like 

 pyramids above the surrounding country, shallow waters covering 

 large flats, deep excavations extending over considerable parts of 

 the ocean, or narrow chasms, precipitous holes increasing the diver- 

 sity of the bottom of the sea, as mountain chains, volcanic cones, 

 high plateaus, deep valleys, rolling hills, and flat plains modify the 

 aspect of the main land. And all these differences, all these pecu- 

 liar features have been introduced gradually and successively by the 

 combined action of the elevation of the land, and recession of the 

 sea ; by the uplifting of the solid crust by volcanic and plu tonic 

 action, and by the abrading influence of water currents, and the 

 regular undulations of the ocean tides. 



Taking the whole globe in its general appearance, we can thus 

 trace to the agency of a few influences, repeated at long intervals in 

 different ways, all the phenomena we observe upon its surface. And 

 the order of succession of the isolated events which have thus modi- 

 fied the surface of our globe has been ascertained with such unex- 

 pected precision, that at present, the relative age of the different 

 geological events is established with as much certainty as the great 

 periods in the history of mankind. 



There is, however, one direction in which these investigations 

 need to be followed out still farther. The secondary events of 

 minor extent and less prominent importance have to be studied with 

 the same precision, and'perhaps with even more detail, than the 

 general phenomena have been, up to the present time. After work- 

 ing out the general history of our globe, we have, as it were, to 

 write its memoirs, the anecdotic part of the relation, and try to 

 contribute in this minute investigation to a fuller illustration of its 

 history. After ascertaining, in a general way, that the elevation of 

 mountain chains, the rise of extensive tracts of land, have marked 

 out the general outlines of continents and their limits with reference 

 to the ocean ; knowing, for instance, that the Scandinavian Alps de- 

 termine the general form of Norway and Sweden ; that Spain is 

 separated from France by a high mountain range ; that it owes its 



