PLANT ARCHEOLOGY. 273 



vierges clu Bre"sil et de Java, aux valines profondes du Nepaul, aux 

 savanes noyees de l'Orenoque, ou la vie surabonde, ou une lumiere 

 ardente, vive et doree, ondule de toutes parts, souleve de tiedes 

 vapeurs, joue avec l'ombre, et fait resplendir les formes des plus 

 merveilleux vege'taux! Sous les tropiques, l'homme se sent ecrase" 

 par une vie exuberante, il lutte incessament pour maintenir sa place 

 au milieu de la nature, dout il est domine" ; ses plus fortes eeuvres sont 

 envahies en peu de temps ; les arbres immenses reprennent possession 

 du sol, des que celui-ci est abandonne" a lui-meme. Dans l'extreme 

 Nord, la faiblesse de l'homme est encore plus eVidente, mais c'est 

 du poids de la nature inerte qu'il est accable". Les elements regnent 

 seuls dans ces regions deVastees, oil l'atmospliere se trouve livree a 

 d'epouvan tables tourmentes. La neige derobe les asperites du sol, la 

 glace couvre la mer d'un sol factice, souvent mobile et toujours dan- 

 gereux ; la confusion est partout, le calme nulle part ; cbaque pas est 

 penible, la vie elle-meme devient un effort que l'energie la mieux 

 trempee ne peut soutenir longtemps sans succomber." (p. 212.) 



The modifications of this contrast through the actual dis- 

 tribution of land and water, winds and currents, are then con- 

 sidered. As these have a fixity secondary only to the funda- 

 mental elements of climate, — namely, the heat of the sun, the 

 inclination of the earth's axis to the plane of its orbit, and 

 the relative density of the atmosphere according to the eleva- 

 tion of the land-surface, — the climate of any part of the world 

 might be supposed to have been constant, oscillations excepted, 

 through the long periods that have elapsed since existing 

 species or their immediate ancestors were introduced. It is 

 not very long ago that Arago demonstrated, to his own and 

 the general satisfaction, that there has been no appreciable 

 change of the earth's climate iu man's time. Plants are the 

 thermometers of the ages, by which climatic extremes and 

 climates in general through long periods are best measured. 

 For at least five or six thousand years the Vine and the Date- 

 palm have grown in proximity, and have furnished grapes 

 and dates to the inhabitants of the warmer shores of the 

 Mediterranean. Yet a very moderate change either way in 

 the temperature would have excluded the one or the other. 

 So Arago concluded that man had witnessed no sensible 

 changes in the climate of Europe ; a good conclusion, if re- 



