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THE POPULAR SCIENCE MONTHLY.

ly urged as would not only justify the use of the genealogical diagram against which be 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 afforded his readers.

It was the strictures of Agassiz above referred to that led Professor W. K. Brooks[1] to write a paper on the subject of "Speculative Zoölogy," 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, stripping our science of all that renders it worthy of thinking men, to become 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 General 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 Professor 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 many 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 monstrous 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,[2] "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

  1. "Popular Science Monthly,' vol. xxii, pp. 195, 364.
  2. "American Journal of Science and Arts," vol. xiv, p. 99.