30 



THE WORLD OF LIFE 



CHAP. 



completely ice-clad during the glacial epoch, while much of 

 southern Britain was free. Germany is poorer than France, 

 partly on account of its severer continental climate, but also 

 owing to France possessing a greater variety of surface, owing 

 to its including a portion of the loftiest Alps in the south-east, 

 the isolated Pyrenees in the south, the Jura and Vosges 

 mountains on the north-east, and its central volcanic ranges, 

 together with its southern Mediterranean coast, and a very 

 extensive western and northern coast-line. It also has a 

 more diversified soil, owing to far less of its surface being 

 buried under glacial debris. Italy has still greater advan- 

 tages of a similar kind, and its slight superiority to France, 

 with less than half the area, is about what we should expect. 

 It well illustrates the fact, already ascertained, that difference 

 of area within moderate limits is of far less importance than 

 comparatively slight advantages in soil and climate. 



Turning now to North America, the following figures 

 from the latest authorities have been supplied by my friend 

 Mr. T. D. A. Cockerell :— 



Effect of Latitude. 



Area, 



Square Miles. 



Montana and 

 stone Park . 

 Nebraska 

 Colorado 

 California 



Yellow-" 



No. of 

 Species. 



1934 



I 50,000 



118,000 1478 



104,000 2872 



158,000 2700 



Two subdivisions of the eastern United States show well the effects 



of latitude. 



Remarks. 



Data in 1900 

 1898 



» 

 »> 



1900 

 recent 



Central and north-east' 

 States — Michigan to 

 Virginia, Kentucky 



South-east United States . 



736,000 

 630,000 



3298 

 6321 



Recent estimate 



The number of species in proportion to area and position 

 is apparently less than in Europe, though the corresponding 

 latitudes are farther south. Germany and Switzerland com- 

 bined, with an area less than one-third of the north-eastern 

 and central States, have about as many species ; while France, 



