32-2 



SCIENCE 



[N. S. Vol. XXIX. No. 739 



Europe. That peninsular region stretches 

 east of the Mississippi Valley, the region 

 of the Great Lakes and Hudson Bay, and 

 there are doubtless more pronounced geo- 

 graphical differences between this articu- 

 lated part and the continental part of 

 North America than between peninsular 

 North America and peninsular Eurasia— 

 that is, Europe. 



Europe gets its characteristic features 

 from some invasions of the sea. Northeast 

 of Scandinavia a part of the Arctic Sea 

 penetrates into the land and branches here 

 as the White Sea. Farther south the very 

 edge of the continent seems to be inundated, 

 so that Great Britain and Ireland are iso- 

 lated, and from the German Sea the Baltic 

 Sea extends far into the interior of the 

 continent. Still farther south is the Medi- 

 terranean Sea, which separates Europe 

 from Africa. All these features seem to 

 be repeated on the west side of the Atlantic. 

 Here we see the Arctic water penetrating 

 far to the south, foi-ming Hudson Bay. 

 Farther south the eastern corner of North 

 America is inundated; Newfoundland is 

 isolated, like Great Britain; and the Gulf 

 of St. Lawrence extends far into the in- 

 terior of the country, getting its waters 

 from that remarkable group of lakes which 

 in many respects resemble the Baltic Sea. 

 This resemblance was far stronger at the 

 end of the last geological epoch, when a 

 vast body of fresh water existed instead of 

 the Baltic Sea which poured through the 

 river valley of the Sund between Denmark 

 and Sweden into the basin of the German 

 Sea. The resemblance of the Gulf of 

 Mexico to the Mediterranean is such a 

 striking one that Alexander von Humboldt 

 called it a mediterranean sea; and, indeed, 

 it divides America into two separate conti- 

 nents—North America and South America. 



These similarities between Europe and 

 peninsular North America are not merely 

 superficial ones. In a very remarkable 



way, these tAvo sides of the Atlantic repeat 

 the same structural features; there is an 

 astonishing symmetry, as Eduard Suess has 

 shown so clearly. The northeast of Canada 

 and Labrador on one side, and Scandinavia 

 with Finland, the region of Feno-Scandia, 

 on the other, are both composed of the old- 

 est rocks we know of. These have a very 

 complicated structure, being intruded with 

 many eruptive rocks, and in a secondary 

 way only, the surface features of the above 

 regions are dependent on their structure. 

 Both regions had already been leveled 

 down before Cambrian times, and they sink 

 gently down under a cover of horizontal 

 Paleozoic strata. Both were called by 

 Suess shields. The resemblance between 

 these shields is the more conspicuous be- 

 cause both were covered during the last ice 

 age by a glaciation which molded their 

 surface in a similar way. In Sweden and 

 Finland we find the same rounded glaci- 

 ated surface, the same numerous lakes, as 

 in Canada, both regions of the earth claim- 

 ing to be the land of the many thousand 

 lakes. At the border of both regions the 

 horizontal Paleozoic strata begin with an 

 escarpment which is pronouncedly devel- 

 oped south of Lake Erie and south of the 

 Gulf of Finland, called here the "glint," 

 and we shall keep this expression to desig- 

 nate similar escarpments. These strata 

 continue far into the interior of Eurasia, 

 and they do the same in North America. 



In the same way that we compare the 

 Canadian Shield with the Scandtaavian 

 Shield we can compare the region east of 

 the Mississippi Valley with the interior of 

 Russia— both parts of the world have never 

 been compressed by mountain-folding since 

 Paleozoic time. Only a few faults occur 

 here, and the whole geological history con- 

 sists in slight up-and-down warps which 

 brought both regions several times under 

 the surface of the transgressing ocean. 

 Also, here the younger geological history 



