138 RELATIVE GEOLOGICAL ANTIQUITY OF TREES. 



there is the requisite amount of moisture. In addition to the 

 leaves of the "Willow, those of the Elm and Maple trees have 

 been found. "We also meet with fragments of dicotyledonous 

 wood, marked by perforations of marine animals. 



With the Chalk we close, as it were, the second great series 

 of volumes of the history of the animal and vegetable crea- 

 tion. Every thing up to this point belongs to the past. The 

 fossils, both animal and vegetable, all belong to species no 

 longer in existence ; they are the fossil remains of extinct spe- 

 cies. "With the commencement of the Tertiary formation a 

 new condition of things obtains, and new forms of life make 

 their appearance, beautifully adapted to the ever-changing 

 landscape, some of them belonging to species now in existence, 

 and occupy the places of that organized life which has forever 

 passed away. 



We have shown that in the earlier periods of the earth's 

 formation the climate was nearly uniform over the whole 

 earth, because it was not determined by the sun, but by the 

 interior heat of the earth. In the Secondary epoch the influ- 

 ence of the sun was hardly yet felt, although the earth had so 

 far cooled as to be more susceptible to outward influences, 

 and the atmosphere had become, comparatively speaking, 

 clearer and more pure. But at the time of the formation of 

 the Tertiary beds, the earth had cooled to such a degree that 

 the effects produced by its internal heat had almost entirely 

 ceased, and the heat received by its surface was mainly derived 

 from the sun. Then arose that diversity of climate which is 

 characteristic of the present creation. The sun gradually ac- 

 quired his rightful empire over the world, and all Nature 

 became dependent on his kindly influences. 



The poles of the earth, which obtain the least amount of 

 sunlight, were necessarily cooled more rapidly than the beds 

 of land at the equator, where the greatest amount of light and 

 heat is received, whilst the zone intermediate between the 

 polar and equatorial regions, where the conditions calculated 

 to develope a superior race most abound, became, in course 

 of time, fitted for the reception of humanity, science, and 

 civilization. 



