134 R. Pumpelly—Secular Rock-disintegration. 
hundred to several hundred feet. Even the wagon roads 
become, in time, depressed to a depth of fifty feet and more by 
the removal of the dust by wind. 
here is one more peculiarity of the loess—it not only is 
wholly unstratified, but it contains the remains of only land 
animals, and especially of Jand snails. Alexander Braun ex- 
amined 211,968 specimens of shells from the loess of the Rhine 
between Basel and Bonn, and found that all were land snails 
except only thirty-three individuals, consisting of Limnea 
Planorbis and Vitrina, which came from three isolated points in 
the valley of the Rhine and Neckar. 
The leess, first well known in the valley of the Rhine and in 
France, was recognized later in other parts of Europe and in 
the Mississippi Valley. It was always looked upon as a sub- 
aqueous formation. Fourteen years ago I observed and after- 
ward described some of the great lcess-basins along the bound- 
aries between China and Central Asia. I was lead to the con- 
material is very nutritive and supports the grass of the steppe 
the dust left by the winds and the hill-wash are arrested by 
the grass which they gradually bury while forming the soil for 
new —— In this way, portions of the country become 
in their own and their neighbor’s debris. Great thick- 
nesses thus gradually accumulate undergoing a transformation 
into loess by the rootlets and stems of the vegetation. | will 
