132 EELATIVE GEOLOGICAL ANTIQUITY OF TREES. 



periods of time, the attractive forces gradually predominated 

 over the repulsive, the nebulous matter condensed about a 

 common centre, evolved heat and light, and the earth became 

 a radiant star or self-luminous body. Another cycle of ages 

 elapsed, during which there was a continual loss of heat from 

 the surface by free radiation into the stellar spaces ; and that 

 surface was ultimately cooled down to the solid crust which 

 now envelopes the fiery nucleus. The earth is therefore an 

 opaque or dark body ; and if these views be correct, it is an 

 extinguished star. 



About the time that the solid mantle of rock was formed 

 through the cooling of the earth's crust, the air and water 

 were probably separated, the atmosphere was charged with 

 carbonic acid, and the clouds burst in violent showers of rain, 

 originating a hot salt sea. The rind continued to grow thicker 

 as the cooling process went on. In the meanwhile, it became 

 necessarily fissured or cracked in many places, and an uneven 

 surface thus originated, with elevations and depressions and 

 openings, through which poured itself a part of the fiery 

 contents of the earth's nucleus. The earth during this period 

 was covered with an immense number of volcanoes, which 

 were constantly engaged in throwing up showers of ashes, 

 incandescent rocks and melted lava, thus increasing the in- 

 equalities of the surface, and forming, in connection with the 

 operation of the boiling waters of these ancient seas, the 

 laminated or slaty rocks known to Geologists as gneiss, mica- 

 slate, and talcose-slate. Their formation closed the first great 

 geological period, the Azoic period. 



Sublime and terrible must have been the scenery during 

 this epoch ; innumerable active volcanoes incessantly thunder- 

 ing, and illuminating the darkened heavens with their raging 

 fires. In such a condition of things, it was impossible that 

 organic bodies, animals and plants, should exist, and accord- 

 ingly we find no traces of them in these ancient rocks. 



In order for living beings to diffuse themselves over the 

 earth, the temperature must be lessened, and an earthy soil 

 must be created, on which plants can grow, and through them 

 animals be nourished. Plants live on inorganic matter, on 



