Geology and Mineralogy 643 



trine of base levels, and the definition of antecedent, conse- 

 quent, and superimposed drainage. These ideas have proved 

 richly fruitful. As they have been developed by Gilbert, 

 Davis, and others, they have marked an epoch in dynamical 

 geology. With, perhaps, the exception of Dana's doctrine of 

 the permanence of continents, these conceptions in regard to 

 drainage have been the most characteristic contribution to 

 geologic science which this country has made. Nowhere else 

 in the world could these ideas have been so well developed as 

 in presence of the gigantic, yet strangely simple, features of 

 the plateau country through which the Colorado and its tribu- 

 taries have carved their way. The doctrine of base levels is 

 as natural a development of the American cordillera as the 

 notion of plains of marine denudation is of the wave-beaten 

 island of Great Britain. 



It is, indeed, probable that the course of the Green River 

 through the Uinta Mountains is not a perfectly uncomplicated 

 example of antecedent drainage. Probably Davis is correct in 

 saying that "the mountains wrenched the saw that afterwards 

 cut them in two." It may even be true, as supposed by Em- 

 mons, 2 that the river is superimposed, rather than antecedent. 

 But, however this may be, the formulation of the general prin- 

 ciples of drainage in the exploration of the Colorado has been 

 no less truly epoch-making in its influence. 



III. THE NATIONAL MUSEUM 



THE collections of the National Museum have exerted a potent 

 influence in the advancement and diffusion of knowledge in 

 the geologic as in other scientific fields. The treasures 

 gathered by the various exploring expeditions, and studied 

 under the direction of the Institution by specialists both 



1 National Geographic Magazine, Volume II, page 103. 

 2 " Report of the Geological Exploration of the Fortieth Parallel," Volume II, page 197. 



