20 THE HISTORY OF CREATION. 



down to the present day — into a hundred equal parts, and if 

 then, corresponding to the thickness of the systems of 

 strata, we calculate the relative duration of the time of the 

 live main divisions or periods according to percentages, we 

 obtain the following result : — 



I. Arcliilithic, or primordial period 



II. Palaeolithic, or primary period . 



III. Mesolithic, or secondary period 



IV. Csenolithic, or tertiary period . 



v. Anthropolithic, or quaternary per.od 



53.6 



32.1 



11.5 



2.3 



0.5 



Total ...■ 100.0 



According to this, the length of the archilithic period, 

 during which no land-living animals or plants as yet existed, 

 amounts to more than one half, more than 53 per cent.; on the 

 other hand the length of the anthropolithic era, during which 

 man has existed, amounts to scarcely one-half per cent, of 

 the whole length of the organic history of the earth. It is, 

 however, quite impossible to calculate the length of these 

 periods, even approximately, by years. 



The thickness of the strata of mud at present deposited 

 during a century, and which has been used as a basis for 

 this calculation, is of course quite different in different parts 

 of the earth under the different conditions in which these 

 deposits take place. It is very slight at the bottom of the 

 deep sea, in the beds of broad rivers with a short course, and 

 in inland seas which receive very scanty supplies of water. 

 It is comparatively great on the sea-shores exposed to strong 

 breakers, at the estuaries of large rivers with long courses, 

 and in inland seas with copious supplies of water. At the 

 mouth of the Mississippi, which carries with it a consider- 



