ORIGIN OF THE LOI<:SS 141 



4. The structure of the loess, as well as its fossils, indicate only land 

 agencies. 



AQUEOUS ORIGIN OF THE LOESS 



Without attempting here to show the weakness of the eolian hypothesis, 

 I will mention some of the facts which api3ear to sustain the aqueous. 

 The first and most significant fact bearing on the origin of the loess con- 

 sists in this, that there have been two thorough investigations and dis- 

 cussions of the loess by competent geologists, who spent much time and 

 labor on its distribution, mode of transportation, and its origin and rela- 

 tive date. I refer to that of Chamberlin and Salisbury and to that of 

 W J McGee. These long continued and able researches resulted in the 

 adoption of the aqueous theory. The report of Chamberlin and Salis- 

 bury is published in the Sixth Annual Report of the United States Geo- 

 logical Survey, and the report of McGee in the Eleventh Annual Report 

 of the same survey. These reports, which for thorough, impartial, and 

 patient research, will long remain classics of American glacial geology, 

 can not lightly be set aside.* 



In the second place, it is found that the loess is a direct and contem- 

 porary variation or derivative from till. It was in 1877 that the writer 

 made the first recorded observation and publication to that effect. In 

 making the survey of Rock and Pipestone counties, in the extreme south- 

 western corner of the state of Minnesota, this most important fact was 

 discovered. 



" The northern part of Pipestone county lies not far from the coteaudes prairies, 

 which is a vast glacial moraine. In traveling southward there is a gradual super- 

 ficial change in all its characters. This change pervades at first but a small thick- 

 ness of the deposit, but by degrees involves the drift to the depth of 20 feet. At 

 first there is a diminution in the number of visible boulders; then a smoothness 

 in the creek bluffs ; then a gravelly clay on the surface, fine and close ; then a close- 

 ness in the prairie soil ; then in digging wells a few limy concretions are seen 

 mingled with small gravel stones, and at last a fine crumbling loam clay which 

 cannot be distinguished from the loess-loam, which extends to iSioux City in Iowa, 

 and there is known as the loess-loam of the Missouri valley. Wells dug in the 

 southwestern part of Rock county demonstrate also a perpendicular transition from 

 loam to drift clay. . . . 



" The writer had abundant and favorable opportunity for observing this change 

 in the grades and cuts of the new railroad from Luverne to the state line, and veri- 

 fied it in wells dug and being dug in that part of the county. In some places the 



♦Professor Chamberlin has more recently modified his views by suggesting what he has desig- 

 nated a " fluvio-eolian" hypothesis, supposing that wind modified and distributed over higher 

 lands the alluvial loess first formed, the whole having been derived by wash from glacial drift; 

 while the loess of China has been found by Professor G. F. Wright to have been originally aqueous, 

 and afterward considerably redistributed by wind, Journ, Geol., vol. v, Nov. -Dec, 1897, pp. 795- 

 802; Bull. Geol. Soc. Am., vol. 13, 1902, pp. 127-138. 



XX— Bull. Geol. Soc. Am., Vol. 14, 1902 



