RECAPITULATION AND CONCLUSION 437 



gauge with some security the duration of these intervals by a 

 comparison of the preceding and succeeding organic forms. We 

 must be cautious in attempting to correlate as strictly contem- 

 poraneous two formations, which do not include many identical 

 species, by the general succession of the forms of life. As species 

 are produced and exterminated by slowly acting and still existing 

 causes, and not by miraculous acts of creation; 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 organism 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 relative, though not actual lapse 

 of time. A number of species, however, keeping in a body might 

 remain for a long period unchanged, while within the same pe- 

 riod, several of these species, by migrating into new countries 

 and coming into competition with foreign associates, might be- 

 come modified; so that we must not overrate the accuracy of 

 organic change as a measure of time. 



In the future I see open fields for far more important researches. 

 Psychology will be securely based on the foundation already well 

 laid by Mr. Herbert Spencer, that of the necessary acquirement 

 of each mental power and capacity by gradation. Much 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 independently created. To my 

 mind it accords better with what we know of the laws impressed 

 on matter by the Creator, that the production and extinction of 

 the past and present inhabitants of the world should have been 

 due to secondary causes, like those determining the birth and 

 death of the individual. When I view all beings not as special 

 creations, but as the lineal descendants of some few beings which 

 lived long before the first bed of the Cambrian system was de- 

 posited, they seem to me to become ennobled. Judging from the 

 past, we may safely infer that not one living species will trans- 

 mit its unaltered likeness to a distinct futurity. And of the species 

 now living, very few will transmit progeny of any kind to a far 

 distant futurity; for the manner in which all organic beings are 

 grouped shows that the greater number of species in each genus, 

 and all the species in many genera, have left no descendants, but 

 have become utterly extinct. We can so far take a prophetic 

 glance into futurity as to foretell that it will be the common and 



