74 



THE AMERICAN NATURALIST 



[Vol. XLVII 



distribution of these curiously endowed stones has been 

 largely brought about through their possession of the 

 floating adaptation. 



Probably a geologist would not mention adaptation in 

 this connection ; he might succinctly state the apparent 

 specific gravity of pumice, and might then proceed to pre- 

 sent the case in terms of this internal character and in 

 terms of more or less quantitatively known features of 

 the surroundings ; for the idea of adaptation here takes 

 account of the low specific density of the rock and the 

 ability to float upon water implied thereby, and to state 

 that pumice is adapted to float is redundant, after we 

 know its specific density. For aught I know also, there 

 may be different species of pumice, some of which might 

 be observed to float higher or a longer time upon water, 

 and in such case, what we might term the varying de- 

 grees of adaptation in the different species should be 

 quantitatively brought out — and then dismissed — by an 

 adequate study of the internal qualities of the rocks. 



But not nearly all of the potentialities discoverable in 

 natural objects are of this realized, and consequently di- 

 rectly observable sort. The future is no doubt pregnant 

 with hitherto untested adaptations and our imagination 

 frequently suggests these as problems. Of course mod- 

 ern natural science responds to the proposal of this sort 

 of adaptation, try it and see if it is true, and many of us 

 are busy just now in doing this very thing. 



If we find observational proof of the suggested prop- 

 erty, interest in its adaptational aspect fades, for the 

 case then passes over into my first category, of actually 

 observed adaptations. Also, the experimental test of a 

 proposed potentiality— as to whether it is attributable or 

 not to the object considered— is but a ease of observation, 

 properly prepared for. Not readily finding the necessary 

 conditions and the object together in nature, we find 

 them separately (at different places or times) and pro- 

 ceed to bring them together. Thus my first experience of 

 the Salton valley was had at a time when it contained 



