62 De Vi Physica 



dications, we argue, that there is between 

 them a real family relationship, a true 

 genealogical filiation : that the later were 

 lineal descendants of the former ; reasoning 

 inductively from some cases when we seem 

 to see, though dimly, the line of descent, 

 to all the others, the vast majority, where 

 we cannot see it at all. But when we at- 

 tempt to go into details, the way is blocked 

 as it were by a door of iron. As if on pur- 

 pose to mock us, in exactly the two points 

 of all the most interesting, the most vital 

 to be known, geology is dumb. What is the 

 meaning, and what were the causes, of those 

 mysterious periods of discontinuity, the geo- 

 logical BREAKS? By what organic alchemy, 

 and under what conditions, assuming that 

 the later forms issued from the loins of the 

 earlier, was the actual metamorphosis per- 

 formed ? For by heaven and earth ! it is 

 very strange. Who ever saw an animal give 



