PHYSICAL GEOGRAPHY. 



due to solar light and heat, decreases, as a general 

 rule, in a regular gradation from the tropics to the 

 poles. It is owing to the greater or less exposure 

 to the sun that we have such a variety of seasons 

 and of climates in different latitudes, and no one can 

 contemplate this wise arrangement without enlar- 

 ging his conceptions in regard to the wisdom and 

 benevolence of the Supreme Being. From numer- 

 ous geological phenomena, it has been concluded 

 that the temperature of the earth has undergone im- 

 portant changes. This supposition rests chiefly on 

 the discovery of vegetable and organic remains, im- 

 bedded in situations where, from the want of a conge- 

 nial temperature, such animals or vegetables would 

 now be unable to exist. For example, tropical 

 plants and fossil elephants are found in great quan- 

 tities in high northern latitudes, in such a state of 

 preservation that it seems next to impossible that 

 they could have been drifted there from a distance. 

 In accounting for this phenomenon, Mr. Herschel, the 

 astronomer, considers that a diminution of the sur- 

 face temperature might arise from a change in the 

 ellipticity of the earth's orbit, which, though slowly, 

 gradually becomes more circular. Mr. Lyell, again, 

 supposes that this decrease of temperature might 

 arise from such a variation in the relative position 

 of land and water, and in the elevation and form of 

 land, as may cause the climate, in any given portion 

 of the earth's surface, so to change, that a greater 

 heat may precede a less heat, and the land be capa- 

 ble of supporting the vegetables and animals of hot 

 climates at one time, and incapable of doing so at 

 another. It supposes a combination of external and 

 internal causes ; the latter raising or depressing the 

 land in the proper situations, the former supplying 

 the necessary heat. This, though a highly ingenious 

 theory, and not without some slight support from 

 facts, is yet too improbable to meet with much fa- 

 vour. It cannot be denied, however, that there is 



