te BULLETIN OF THE 



•pears as upheaval it is but little faster than atmospheric degra- 

 dation, but such faulting may he paroxysmal and intermittent. 



III. Faults discovered by the position of monoclinal ridges 

 have been erroneously explained as " lateral faults." The 

 position of the ridges is in fact due to vey^tical faults by which 

 two parts of the same flexure are differentiated, the region 

 having the greatest amplitude of flexure having its monoclinal 

 ridges curved farther back from the axis of upheaval. 



lY. If the rate of upheaval is greatly accelerated, the rate 

 of degradation is greatly accelerated. If in two parts of an anti- 

 clinal upheaval, the one has an upheaval exhibiting 10,000 feet, 

 the other 20,000 feet, the latter, ceteris paribus, will have a 

 general surface but slightly elevated above the former. In other 

 words, the rate of degradation is chiefly determined by the rate 

 of displacement. 



Mr. C. E. Button complimented Mr. Powell on the character 

 of his work, and on the interesting results obtained by him ; and 

 proceeded to remark on some of the peculiar features of the geol- 

 ogy exhibited in the Colorado region. Not only were these fea- 

 tures on a scale perhaps nowhere else exhibited — as, for example, 

 in the range of palpable denudation and erosion, in the channelled 

 canons extending for hundreds of miles, and as much as a mile 

 deep or even more, in the great faults of several thousand feet 

 displacement, reaching for several hundred miles, etc. ; but the 

 features were more exposed to observation, being less disguised 

 superficially by vegetation, etc , as if here the geologist had 

 found nature in her nakedness. Hence this great region was pre- 

 eminently favorable to geologic study, and permitted results to 

 be arrived at which elsewhere would require a far longer and 

 more tedious process of exploration. 



Mr. W. B. Taylor remarked that the results brought to view 

 by Mr. Powell in his extensive reseai'ches and ingenious exposi- 

 tions, appeared indirectly to have quite an important bearing on 

 the much disputed question of the thickness of the earth's crust. 

 He (the speaker) had himself been disposed for some time past 

 to abandon the idea of a large amount of solidity or rigidity in 

 the earth, as supported by the plausible mathematical argument 

 of the distinguished physicist and mathematician, Mr. Hopkins, 

 and to recur to the earlier conception of a very thin crust resting 

 upon or enveloping a molten and fluid spheroid. Every geologi- 



