412 T. C. CHAMBERLIN 



carries a certain measure of presumption that the amphibians 

 were fresh-water derivations. 



In this larger application of the interpretation herein sug- 

 gested, the chordate phylum is made to be essentially from first 

 to last a terrestrial race, whose main habitat was the land waters 

 and the land itself, though still a race that sent its offshoots 

 down to sea from time to time from the mid-Paleozoic onwards. 



The large hypothetical element in the foregoing interpreta- 

 tion is sufficiently evident and needs neither word of caution 

 nor apology. The problem at present admits of no other than 

 hypothetical treatment. The discussion is merely the attempt of 

 a geologist to interpret from the geologic side the imperfect data 

 that bear obscurely on the habitat of the early vertebrates. 



T. C. Chamberlin. 



