HOW PHENOMENA ARE INTERPRETED. 69 



of the earth are changing slowly. In time they can change 

 to an unlimited extent. Geologists explain all geologic phe- 

 nomena as due to physical causes such as are now going on ; 

 but the implication is that, given simply time, everything 

 we observe of this character is easily understood, with no 

 appeal to other than such factors as are at work before our 

 eyes, and, with such a background as is afforded by an appeal 

 to astronomy, there is good reason for holding that no other 

 physical factors than the ordinary type have been involved in 

 the geologic phenomena. Geological facts are explained by 

 presenting their physical antecedents, and the explanation stops 

 when traced to these, that is to say, when in the territory of 

 astronomy or physics. 



Once more : only a generation ago men believed that all 

 species of animals and plants upon the earth were descended 

 from similar forms without modification from the original ones 

 created by fiat. The horse of to-day is like his ancestor of 

 thousands of years ago, the lily like the original. In like 

 manner all plants and animals and men represented in form 

 and qualities their prototypes. Not because any one had ever 

 been a witness to such a process of creation nor because there 

 were other evidences which deserved attention, but it was a 

 kind of habit of mind to pretend to explain phenomena by 

 referring to some inexplicable process out of all relations with 

 experience. In 1846 a book was published anonymously, called 

 Vestiges of Creation. It attempted to show that all the present 

 forms of life might have resulted from the simplest forms of 

 life by a series of small, almost insensible changes in the 

 organisms, if these were continued for a great number of 

 generations. The idea was condemned by almost everybody 

 interested in the question, not from defective evidence, but 

 simply because it required the abandonment of a belief that 

 had not a particle of evidence in its favor. That is to say, an 

 attempted explanation which had much experience in its favor 

 was rejected by theologians and naturalists alike, and another 

 explanation, having not a particle of evidence and no degree of 

 probability, was held to. Since the time of Darwin all that 

 has been changed. The view advocated in Vestiges, though not 



