574 KANSAS CITY REVIEW OF SCIENCE. 



away the mountain has been elevated 3,000 feet above the river. The time re- 

 quired for all these changes must far exceed all our conceptions of duration. 



It is an undoubted fact that the topography of the present surface of the 

 earth has been largely affected by erosion. This process is constantly going 

 -on, degrading the eminences, changing the declivities, and gradually wearing 

 away the whole surface of the land. The sum of this erosion, since the last 

 great geological changes, is enormous. The amount of erosion over many por- 

 tions of England is estimated at xo,ooo to 11,000 feet. 



In the Appalachian region it is proved that the erosion has amounted in 

 some cases to not less than 20,000 feet in depth. In portions of the Rocky 

 Mountain regions this erosion has been still greater. Professor Powell informs 

 «s that in the Uintah region the amount of erosion has exceeded five miles in 

 depth in some places, with an average depth of three and a half miles over 

 2,000 square miles of country. The time necessary for the removal of so large 

 an amount of material of course would depend on the agencies employed and 

 she energy with which they operated. It would undoubtedly be vast. 



Water, aided by frost, is probably the principal agent operating in produc- 

 ing all the erosion that has taken place on the earth. The power of water to 

 '^' wear away a stone" is witnessed in the wonderful channels' they have cut for 

 themselves during the present geological age. The Niagara River has cut a 

 channel about 200 feet deep a distance of seven miles. Mr. Lyell estimates 36, 000 

 years as the time necessary for the accomplishment of the task ; but as we know 

 neither the present nor the past rate of progress the river has made, such esti- 

 mates are perfectly unreliable. 



A very noted example of river erosion is exhibited by the Grand Canon of 

 "ihe Colorado River, which is 300 miles long and from 2,000 to 6,000 feet deep. 

 But we have no data from which to estimate the time required for the river to 

 cut its way through this distance of rock. We do not know the present rate of 

 recession, nor do we know but the river simply followed and enlarged a crevasse 

 that had been formed by some convulsion of nature. As all such data are unre- 

 liable, all conclusions drawn from them must be fallacious. 



The general erosion of the whole surface of the earth may be estimated by 

 measuring the amount of sediment that is now carried down by the rivers of the 

 globe. As we have previously stated, the amount of materials composing the 

 sedimentary rocks is the amount that has been eroded. This, it is estimated, 

 would be equivalent to 2,000 feet in depth over the whole surface of the earth; 

 and if taken from the present land surface, it would equal an average of not less 

 ■than 6,000 feet over the whole land surface. The average erosion of the general 

 surface of the earth as estimated from river sediment cannot be less than one 

 foot in 5,000 years. At this rate it would require, to remove an average thick- 

 ness of 6,000 feet no less than 30,000,000 of years. And this is tl;e estimate 

 some would place on the age of the earth, since the first sedimentary rocks were 

 laid down. 



But two facts present themselves for consideration here, that go far to vitiate 



