INTRODUCTORY OBSERVATIONS. 13 



upon as indicating an analogy in the climate. It is now, 

 to be sure, somewhat inaccurately said by botanists, that a 

 mountain is high enough to enter " into the region of the 

 rhododendrons," just as it was fonnerly said that such a 

 mountain attained to the Hmits of perpetual snow, — an 

 erroneous mode of expression, as admitted by Humboldt, 

 if it be thereby meant to intimate that under the influence 

 of a certain temperature, or any other climatic influence, 

 certain vegetable forms must of necessity be developed. 



Heat and cold certainly produce very different eflfects 

 upon different species of living creatures. A quadruped or 

 bird which has its centre of dominion or characteristic 

 locality in a temperate region will be so far influenced by 

 an amelioration of climate as to extend its range somewhat 

 farther north, under a meridian where, from local causes, a 

 ereater warmth prevails than is customary in the same 

 deorree of latitude ; but a truly northern species, which 

 dwells by preference " in thrilling regions of thick-ribbed 

 ice," would rather extend southward on a meridian line 

 of more than usual coldness. The one would advance in 

 the direction of the Pole, attracted rather than driven 

 northwards by the increase of temperature ; the other 

 would migrate in a southerly direction, not to avoid but 

 to accompany the cold. Thus the musk-ox, one of the most 

 remarkable of the North American animals, which affects a 

 cold and barren district where grass is replaced by lichens, 

 owin<T to the greater mildness of the climate, does not 

 rantre so far to the southward on the Pacific coast as it 

 does on the shores of Hudson's Bay ; for it is neither 

 found in New-Caledonia nor on the banks of the Columbia, 

 nor does it occur on the rocky mountain-ridge at the 

 customary crossing-places near the sources of the Peace, 

 Elk, and Saskatchewan rivers. 



In tracing each parallel throughout its whole extent we 

 shall find, as we advance from the polar and temperate to 

 the equatorial regions, that the species become restricted 

 in their distribution, and that although they may occupy in 

 reality as great an extent of actual space, they yet extend 

 over a smaller portion of the earth's circumference. Thus 

 in the northern hemisphere we find the wolf, the seal, the 

 walrus, and the Polar bear, occupying a large portion 

 of the entire circumference of the higher latitudes, from 



Vol. III.— B 



