Lli CONTE.l 



Critical Periods. 



323 



ogists do not recognize the greatness of the change. If it were 

 farther away, already completed, and the records of the gradual 

 process lost, it would be recognized at once. As the great mass of 

 a mountain range cannot be seen when we are amongst its peaks, so 

 being in the midst of this great change, and seeing it so close at 

 hand we fail to catch the true perspective and recognize its great- 

 ness. 



If, then, the P,sychozoic be acknowledged as an Era, the Quater- 

 nary ought to be united with the Cenozoic rather than the Psycho- 

 zoic. It is true it may be objected, as has been done by Upham,* 

 that man appeared in the Quaternary. The answer to this is, that 

 he had not yet established his supremacy, but still contended doubt- 

 fully with the great mammals of that time. This is in full accord 

 with the cases of other eras. Reptiles appeared first in the Permian, 

 but the age of reptiles commenced only with the Mesozoic. Mam- 

 mals were introduced first in the Mesozoic, but the age of mammals 

 commenced only with the Cenozoic. So man was introduced in 

 the Quaternary and possibly even in the Tertiary, but the Age of 

 Man commences only with the Psychozoic. The changes must not 

 only commence but be substantially completed and a new order of 

 adjustment established, before a new era begins. 



This critical period, as the last, the nearest to us, and therefore 

 the clearest, may be taken as the type. The attentive study of this 

 one ought to throw abundant light on the true nature of critical 

 periods in general. It is, however, the shortest in lapse of time. It 

 is, also, probably the least so far as physical changes are concerned, 

 and therefore also so far as changes of life-forms produced by phys- 

 ical changes, are concerned. But it is by far the greatest of all so 

 far as concerns the effect of its dominant type in determining 

 changes of all kinds. 



We have taken this one as the type and dwelt upon it, because 

 its significance is not generally recognized. The other examples 

 are well known and their importance recognized. They may be 

 easily explained in the light of this one and therefore may be 

 quickly dispatched, especially as I have already treated them fully 

 in the article previously referred to. 



-Am. Nat., 2S, 980, 1894. 



