140 Evolution of Animal Life. 



versa!, and identical effects, or consequents, must be ascribed 

 to identical causes, or antecedents. We are conscious of in- 

 definite liability to mistake in the application of this prin- 

 ciple ; but our faith in it remains unaltered and fundament- 

 al. Hence, when we are able to say with high probability 

 of any phenomenon that it is, together with all related phe- 

 nomena, in all respects exacthj as if it had been caused in a 

 certain way, we conclude, subject to correction from larger 

 knowledge, that it was so caused. 



And while waiting and working for such larger knowledge, 

 we proceed, and are right in proceeding, exacAly as if our 

 inference were correct. In scientific phrase, we make it 

 our ''working-hypothesis." Thus, when we find rocks dis- 

 posed in layers exactly as i/' they had been deposited as sedi- 

 ments of sand or clay from water, we conclude that they 

 were so deposited. When we find in them forms which re- 

 semble perfectly the remains of animals buried in such sedi- 

 ments, we conclude that the bodies of animals were so buried. 

 The monkish fathers, who declared fossils to be but evi- 

 dences of the Almighty power which was able to make such 

 simulacra, to mock the human reason, were as false to 

 religion as to science. God issues no counterfeit bills. 

 The inscriptions He writes — if we can only make them 

 out — are true. The question then is, what do the phe- 

 nomena of animal life and its records in the earth's crust 

 indicate as the probable cause of the present and past variety 

 of species ? 



IV. Admitted Facts. 



It is a remarkable circumstance that there should be so 

 little controversy as to the facts, liowever much opinions 

 differ as to their significance and relative importance. The 

 following list will suffice to recall the facts admitted by 

 all parties. 



A. The lapse of vast periods of time since the intro- 

 duction of aidmal life on the earth. 



B. Continuous change in geological, geographical, topo- 

 graphical, climatic and other conditions, constituting the 

 environment. 



C. The successive appearance of different species, in a 

 certain general order, exhibiting the laws of differentiation, 

 progress of the whole, and cyclical movement. The first 

 law is shown in " prophetic types," or forms combining the 

 characteristics of two groups, which are found to have ex- 



