6 BIOLOGICAL SOCIETY OF WASHINGTON. 



To the modern naturalist, a belief in the universal distribution, 

 and narrow and rigidly restricted chronological range of organic 

 types which characterize each successive epoch, implies that 

 evolution has occurred in all instances in exactly the same mathe- 

 matical ratio ; for animal as well as vegetable forms ; for aqueous 

 as well as for terrestrial life ; for the life of fresh waters as well as 

 that of the seas ; and under every environing condition of climate 

 and of geological change. It implies the existence of some un- 

 known and unexplainable law which, at the close of each epoch, 

 required the utter and speedy extinction of exactly such types as 

 had specially characterized those epochs, even if the physical con- 

 ditions under which they had formerly existed had continued the 

 same. That such ideas do prevail among paleontologists at the 

 present time one has abundant proof in their published writings. 



In Europe it was found that during the successive geological 

 epochs certain types of plants and vertebrate and invertebrate 

 animals all lived simultaneously ; and the actual and relative rate 

 of progress of evolution of the types in each of these great bio- 

 logical divisions, seeming to be a natural one, was regarded as 

 under the influence of some cosmical law which necessarily made 

 that rate uniform for the whole earth. When, therefore, even a 

 single type, whether of plants or vertebrate or invertebrate ani- 

 mals, such as is known to characterize any European group of 

 strata, has been found in any other part of the earth, it has been 

 customary to hold that the animal or plant, as the case might be. 

 which is represented by that type, existed simultaneously with its 

 European congeners. Although the folly of relying upon such 

 slender evidence has again and again been shown, it is not 

 uncommon to see it presented in important paleontological pub- 

 lications with all the force that such words as ik certainly," 

 "undoubtedly," •• unquestionably," &c, can give it. 



I have made the foregoing statements, first, to call attention 

 to the existence of the erroneous views which I have indicated ; 

 and, secondly, that they may serve as a suggestion of the reason 



