CONCLUSIONS. 385 



exclusively on fish, which is not to be obtained without great 

 toil and peril, should present the same characteristics, either 

 bodily or mental, as those who idly regale on the spontaneous 

 bounties of tropical vegetation. 



[ 635. Many other causes still more intimately connected 

 with the aspect of our globe have also a great influence upon 

 the distribution of the animals and plants living on its 

 surface. The form of continents, the bearing of their shores, 

 the direction and height of mountains, the mean level of great 

 plains, the amount of water circumscribed by land, and form- 

 ing inland lakes or seas, each shows a marked influence upon 

 the general features of vegetation. Small low islands, scat- 

 tered in clusters, are covered with a vegetation entirely 

 different from that of extensive plains under the same lati- 

 tudes. The bearing of the shores, again, modifying the cur- 

 rents of the sea, will also react upon vegetation. Mountain 

 chains will be influential, not only from the height of their 

 slopes and summits, but also from their action upon the 

 prevailing winds. It is obvious, for instance, that a moun- 

 tain chain like the Alps, running east and west, and form- 

 ing a barrier between the colder region northwards and 

 the warmer southwards, will have a tendency to lower the 

 temperature of the northern plains, and to increase that of the 

 southern below or above the mean which such localities would 

 otherwise present ; while the influence of a chain running 

 north and south, like the Rocky Mountains and the Andes, 

 will be quite the reverse, and tend to increase the natural dif- 

 ferences between the eastern and western shores of the conti- 

 nent, laying open the north to southern influences and the 

 south to those of the north, thus rendering its climate ex- 

 cessive, i. e. its summer warmer and its winter colder. 



[ 636. Again, the equalizing influence of a large sheet ot 

 water, the temperature of which is less liable to sudden changes 

 than the atmospheric air, is very apparent in the uniformity of 

 coast vegetation over extensive tracts, provided the soil be of 

 the same nature ; and also in the slower transition from one 

 season into another along the shores, the coasts having less 

 extreme temDeratures than the main land. The absolute de- 

 gree of temperature of the water acts with equal power ; as 

 the aquatic plants of the tropical regions, for instance, those 



c c 



