412 LAKE SUPERIOR. 



main land has been lifted above the ocean at different rates in differ- 

 ent parts of the country ; and it would be a most important investi- 

 gation to have their absolute level, in order more fully to ascertain 

 the last changes which our continents have undergone. 



From the above mentioned facts, it must be at once obvious that 

 the various kinds of loose materials, all over the northern hemisphere, 

 have been accumulated, not only under different circumstances, but 

 during long-continued subsequent distinct periods, and that great 

 changes have taken place since their deposition, before the present 

 state of things was fully established. 



To the first period, the ice period, as I have called it, belong 

 all the phenomena connected with the transportation of erratic bould- 

 ers, the polishing, scratching and furrowing of the rocks and the 

 accumulation of unstratified, scratched, and loamy drift. During that 

 period, the main land seems to have been, to some extent at least, 

 higher above the level of the sea than now ; as we observe, on the 

 shores of Great Britain, Norway and Sweden, as well as on the east- 

 ern shores of North America, the polished surfaces dipping under 

 the level of the ocean, which encroaches everywhere upon the erratics 

 proper, effaces the polished surfaces and remodels the glacial drift. 

 During these periods, large terrestrial animals lived upon both conti- 

 nents, the fossil remains of which are found in the drift of Siberia, 

 as well as of this continent. A fossil elephant recently discovered in 

 Vermont adds to the resemblance, already pointed out, between the 

 northern drift of Europe and that of North America ; for fossils of 

 that genus are now known to occur upon the northernmost .point of 

 the western extremity of North America, in New England, in North- 

 ern Europe, as well as all over Siberia. 



To the second period we would refer the stratified deposits resting 

 upon drift, which indicate that during their deposition the northern 

 continent had again extensively subsided under the surface of the 

 ocean. 



During this period, animals, identical with those which occur in 

 the northern seas, spread widely over parts of the globe which are 

 now again above the level of the ocean. But, as this last elevation 

 seems to have been gradual, and is even still going on in our day, 

 there is no possibility of tracing more precisely, at least for the 



