292 THE HISTORY OF 



instance, pour down a vast ravine which has been cut into 

 a terrace of rock ; and Lyell has pointed out, that the 

 waterfall originally, that is at the close of all the revolutions 

 and deluges, discharged the water over the edge of that 

 terrace, and has gradually washed out that ravine since. 

 This must have required a space of time equal to at least 

 20,000 years ; and thus long, under any circumstances, 

 North America must have existed in its present configura- 

 tion and under the same physical conditions. Another 

 similar example has already heen furnished above, in the 

 Coal, and it would be easy to multiply the proofs that 

 the space of time which we, with boastful self-sufficiency, 

 delight to call the World's History, is but the last fleeting 

 moment of the infinitely long lifetime of our little planet. 



If now we recall to mind the sketches above given of 

 the successive epochs of vegetation, we see that the vege- 

 table world begins in water, under the simplest forms, and 

 in that very family in which the whole plant is represented 

 by a single cell, most frequently, in the present time. In 

 the succeeding periods the other groups are added to this, 

 making their appearance in a series which corresponds 

 through a continually higher organization, i. e., continually 

 more manifold vital processes, to the successively more 

 manifold and complicated physical conditions which come 

 into action. Thus the stemless Cryptogamia are followed 

 by those provided with stems and leaves. Then the 

 Gymnospores (Conifers and Cycadese) enter upon the 

 field ; to these succeed the Monocotyledons, and lastly 

 appear the Dicotyledons. Imperfect as are the documents 

 we have obtained, and little as we have yet decyphered of 

 them, yet in no period do we find the appearance of a 

 wholly new creation, but the organic beings are always 

 , added gradually; the lowest members of one period sue- 



