244 



SCIENCE 



[N. S. Vol. XLI. No. 1050 



Professor R. M. Barton, of the University 

 of New Mexico, has been appointed professor 

 of mathematics in Lombard College. 



DISCUSSION AND COSBESPONDENCE 



THE RATE OF CONTINENTAL DENUDATION ^ 



In an article bearing the above title, pub- 

 lished in Science, December 25, 1914, Charles 

 Keyes contends that determinations of mineral 

 matter carried by such streams as the Missis- 

 sippi are of little or no value, particularly as a 

 basis for estimates of " the rate of lowering of 

 the continental surface through stream cor- 

 rasion" (and transportation?). To the pres- 

 ent writer it seems that the article as a whole 

 and most of the individual statements in it are 

 likely to give many readers a wrong impres- 

 sion, and that some of the statements, for ex- 

 ample that " The elaborate stream measure- 

 m.ents thus go for naught " are altogether and 

 demonstrably untrue. 



The great practical value of the water anal- 

 yses is too obvious to need elucidation. They 

 are essential in water-supply problems almost 

 innumerable, especially in connection with 

 providing water for industrial and municipal 

 use, and for irrigation; in fact they were made 

 primarily for use in solving just such prob- 

 lems, not " with the express purpose of deter- 

 mining the rate of lowering " of the land sur- 

 face. The measurements of stream discharge 

 that have been utilized in calculating the 

 rates of denudation furnish the basic data 

 for many of the greatest public and private 

 hydraulic developments in the United States. 



The educational value of the data afforded 

 by these determinations is equally obvious. 

 That the Mississippi is gathering from the sur- 

 face, mostly from the soil, of its own basin sev- 

 eral hundred million tons of earthy material 

 every year and is dumping this material into the 

 Gulf of Mexico; that practically none of this 

 material is being returned; that some parts 

 of the basin are losing by stream action more 

 rapidly than others; that the earth's surface 

 everywhere is being continually modified by 

 such action — valleys carved, hills razed, and 



1 Published by permission of the Director, TJ. S. 

 Geological Survey. 



so on — these are not facts that it is worthless 

 to ascertain. 



Apparently Mr. Keyes wishes to convince 

 his readers that the stream observations that 

 he assails are futile because the effects of 

 stream action are modified by internal earth 

 movements and by the introduction of wind- 

 blown materials. 



That parts of the Mississippi basin have 

 been uplifted in past geologic time is a matter 

 of common knowledge, but the writer does not 

 see that it affects the precision of conclusions 

 regarding the amount of material now being 

 removed by the streams. The statement that 

 " Since Glacial times — perhaps 10,000 years 

 ago — a very considerable part of the upper 

 Mississippi Valley appears to have been ele- 

 vated not less than 500 or 600 feet" must 

 have reference to the remarkable work of late 

 years on raised Pleistocene beaches of the 

 Great Lakes, but the published reports on this 

 work indicate that only a small part of the 

 Mississippi Valley has been affected by the 

 uplift, and none of it so much as 500 or 600 

 feet. The 500- and 600-foot isobases lie en- 

 tirely outside of the Mississippi basin in the 

 vicinities of Lake Superior and Quebec. 



As to wind deposits, it should be remem- 

 bered that strata of other than wind origin lie 

 at or near the surface throughout the Missis- 

 sippi basin, whereas if dust had been accumu- 

 lating " over the entire Mississippi Valley 

 faster than the river and its tributaries are 

 carrying rock waste to the sea," water-laid 

 and ice-laid materials would not outcrop but 

 would be deeply buried under eolian dust instead 

 of under products of their own decomposition. 

 That large quantities of material have been 

 and are being shifted by the wind no one 

 doubts. The literature on the subject is 

 voluminous, as is shown by the excellent bibli- 

 ography compiled by Stuntz and Free, and 

 many precise data have been recorded. For 

 example, J. A. Udden calculated in 1894 that 

 the capacity of the atmosphere over the Mis- 

 sissippi basin to transport dust may be a thou- 

 sand times that of the river, but he did not 

 fail to observe that the actual load carried by 

 the air is " an insignificant fraction " of its 

 capacity load. Dust, however, is shifted back 



