MATERIAL UNIVERSE. 63 



tion of the poles with the equator has been 

 changed ; assuming that a part of the earth, 

 near the poles, emerged from its watery submer- 

 sion before the temperature of the water was 

 reduced below 98 : and the difficulty of ac- 

 counting for the remains of tropical animals and 

 plants, found in the now frigid zones, will at 

 once vanish. 



Again : during the first ages of the earth's 

 existence, when the crust was thin compared 

 with what it now is, the hills not being so much 

 elevated, nor the valleys so much depressed, we 

 may reasonably assume that a very large portion 

 of that under the water was sufficiently shallow 

 to be left nearly dry for a great part of the time. 

 This may account for the existence of amphib- 

 ious animals, not now known ; and for those 

 herbivorous monsters which, from their structure, 

 probably inhabited places partially covered with 

 water. The temperature, at that time, would 

 favor the luxuriant growth of aquatic vegetables 



