no THE POPULAR SCIENCE MONTHLY. 



ly urged as would not only justify the use of the genealogical diagram 

 against which he so strongly inveighed in his admirable address before 

 this Association at the Boston meeting ; but had he adopted this 

 method, a much clearer view of the very points he wished to emphasize 

 would have been aflForded his readers. 



It was the strictures of Agassiz above referred to that led Pro- 

 fessor "W. K. Brooks* to write a pajier on the subject of " Speculative 

 Zoology," in which he most earnestly and ably defends the use of 

 genealogical diagrams, and justly says : "If phylogenetic speculations 

 retard science, speculations upon homology must do the same thing ; 

 and the only way to avoid danger will be to stick to facts, and, strip- 

 ping our science of all that renders it worthy of thinking men, to be- 

 come mere observing machines." 



Since 1876 Professor Marsh and Professor Cope have in various 

 journals and Government publications presented the results of their 

 discoveries of the past vertebrate life of North America. The Gener- 

 al Government has published the two great monographs of Professor 

 Marsh on the Dinocerata, an extinct order of gigantic mammals, and 

 the Odontornithes, an order of extinct toothed birds, as well as Pro- 

 fessor Cope's great volume on the Tertiary Vertebrata, besides other 

 memoirs by the same authors. Space will forbid more than a passing 

 allusion to the varied and remarkable additions to our knowledge of 

 extinct vertebrate life made by these naturalists. 



Had a moiety of the work accomplished by these investigators 

 been known to Geoffroy Saint-Hilaire, the theory of descent would have 

 been established long before Darwin, though to Darwin and Wallace 

 belongs the full credit of defining the true cause. Leidy, Marsh, and 

 Cope have not only brought to light a great number of curious beasts, 

 many of them of gigantic and unique proportions, but forms revealing 

 in their structure the solution of n^any morphological puzzles, and 

 throwing light on the derivation of many obscure parts. 



The discovery in the Western tertiaries of multitudes of huge and 

 monstrous mammals and, earlier still, of gigantic and equally mon- 

 strous reptiles, naturally led at once to an inquiry as to the cause of 

 their extinction. " Nothing can be more astonishing," says Professor 

 Joseph Le Conte,f " than the abundance, variety, and prodigious size 

 of reptiles in America up to the very close of the Cretaceous, and the 

 complete absence of all the grander and more characteristic forms in 

 the lowest Tertiary ; unless, indeed, it be the correlative fact of the 

 complete absence of mammals in the Cretaceous, and their appearance 

 in great numbers and variety in the lowest Tertiary. . . . The wave 

 of reptilian evolution had just risen to its crest, and perhaps was ready 

 to break, when it was met and overwhelmed by the rising wave of 

 mammalian evolution." In this paper of Le Conte's, which is entitled 



* " Popular Science Montlily, ' vol. xxii, pp. 195, 3G4. 



* "American Journal of Science and Arts," vol. xiv, p. 99. 



