RECAPITULATION AND CONCLUSION 439 



attempting to correlate as strictly contemporaneous 

 two formations, which include few identical species, 

 by the general succession of their forms of life. As 

 species are produced and exterminated by slowly 

 acting and still existing causes, and not by miraculous 

 acts of creation and by catastrophes ; and as the most 

 important of all causes of organic change is one which 

 is almost independent of altered and perhaps suddenly 

 altered physical conditions, namely, the mutual relation 

 of organism to organism, — the improvement of one being 

 entailing the improvement or the extermination of 

 others ; it follows, that the amount of organic change in 

 the fossils of consecutive formations probably serves as a 

 fair measure of the lapse of actual time. A number of 

 species, however, keeping in a body might remain for a 

 long period unchanged, whilst within this same period, 

 several of these species, by migrating into new countries 

 and coming into competition with foreign associates, 

 might become modified ; so that we must not overrate 

 the accuracy of organic change as a measure of time. 

 During early periods of the earth's history, when the 

 forms of life were probably fewer and simpler, the rate 

 of change was probably slower ; and at the first dawn 

 of life, when very few forms of the simplest structure 

 existed, the rate of change may have been slow in an 

 extreme degree. The whole history of the world, 

 as at present known, although of a length quite in- 

 comprehensible by us, will hereafter be recognised 

 as a mere fragment of time, compared with the ages 

 which have elapsed since the first creature, the pro- 

 genitor of innumerable extinct and living descendants, 

 was created. 



In the distant future I see open fields for far more 

 important researches. Psychology will be based on a 

 new foundation, that of the necessary acquirement of 

 each mental power and capacity by gradation. Light 

 will be thrown on the origin of man and his history. 



Authors of the highest eminence seem to be fully 

 satisfied with the view that each species has been inde- 

 pendently created. To my mind it accords better with 



