WHITE.] SURFACE FEATUEES PAEKS AND BASINS. 9 



otber displacements of the strata; and both simultaneous and sub- 

 sequent subaerial denudation of the strata thus elevated. The latter 

 process has produced what may with propriety be called the drainage 

 features of the region. These are really the most conspicuous features 

 of all, for the elevated portions of the great flexures have been mostly 

 removed by the erosion just referred to. A part ot^the drainage of this 

 district, like a large part of that of the whole great region within which it is 

 located, is antecedent.* That is, it was evidently established before the 

 principal displacements, including the great flexures, were produced. 

 This view of the subject implies that the flexures were produced very 

 slowly, and that before the strata began to bend the streams were already 

 established upon the surface, and traversed the future sites of the flexures 

 at various angles; aud furthermore, that the streams continued to retain 

 their original positions by a constant erosion, equivalent in amount with 

 the elevation that was in progress. I am not unaware of the weighty 

 objections that may bo urged against this theory, but it seems to accord 

 with the greatest number and most important of known facts. 



It is a most remarkable fact that during this elevation of the strata 

 the streams seem to have been very little influenced in or changed from 

 their courses by either the favorable or unfavorable conditions for 

 erosion of the strata themselves; mountain masses of quartzite not 

 forcing a divergence, nor the softest strata inducing a departure from 

 their predetermined courses. !So far as my observation has yet ex- 

 tended, it is those channels only or mainly which have a greater or less 

 flow of perennial water that are referable to the category of antecedent 

 drainage. On the other hand, the present location of the dry drainage- 

 channels of the region, as well as the unequal depth and extent to which 

 the erosion has reached in them and upon the surface they drain, is 

 largely due to the difference in the lithological characteristics of the 

 strata out of which the surface features have been carved, but modified 

 and controlled by the displacements which the strata have been sub- 

 jected to. In other words, this part of the drainage system is mainly 

 subsequent to or consequent upon the great movements that have 

 resulted in the present displacements of the strata. This "consequent" 

 drainage, although consisting mainly of those numerous minor branches 

 which are dry during a part of the year, has produced present physical 

 features that are scarcely less conspicuous than those which have been 

 produced by all other causes; for by its agency almost all the immense 

 erosion and degradation which the region has suffered has been accom- 

 plished, while the principal streams have served as vehicles for the trans- 

 portation of the material thus removed from the surface. 



PARKS AND BASINS. 



The terms "park" and "basin," as names of geographical features, 

 have been variously and somewhat loosely used by different wi iters. 

 Finding it necessary to use them in this report for purposes of descrip- 

 into, I shall apply the term " park" only to those expansions of the river- 

 valleys that contain more or less broad spaces of comparatively level 

 land, a part of which is susceptible of cultivation by irrigation, and 



* This explanation of the relation that the river-valleys of the great Eocky Mount- 

 ain region generally hold to the displacements that the strata have suffered, by assum- 

 ing that the displacements took place after the rivers were established, vrithout mate- 

 rial change in the course of the rivers, was first suggested by Dr. Hayden in the 

 American Journal of Science and Arts for May, 1862, aud afterward in his Eeport for 

 1872, page 85. The subject was afterward well elaborated by Professor Powell in his 

 reports. 



