VALLEY LOESS AND THE LANSING FOSSIL MAN 559 



GLACIATION IN THE BERKSHIRE HILLS, MASSACHUSETTS 

 BY F. B. TAYLOR 



An abstract is printed in Science, volume xvii, page 225. 



VALLEY LOESS AND THE FOSSIL MAN OF LANSING, KANSAS 

 BY WARREN UPHAM 



[Abstracl] 



The loess in the Missouri and Mississippi valleys is attributed to deposition b}^ 

 these rivers during a time of somewhat lower altitude of this region, at the begin- 

 ning of the Champlain epoch, when the glaciated area of this continent sank from 

 its previously high elevation to be mostly 300 to 500 feet lower than now. By this 

 depression a temperate climate was restored on the border of the continental ice- 

 sheet, which became greatly reduced by its surface melting, so that much of the 

 drift l)efore contained within the ice was at last exposed on the thinned ice-fields, 

 as now on the Malaspina ice-sheet in Alaska. 



The ice- melting and rains probably swelled these great rivers to twice or three 

 times their present average annual volume; and their supply of silt, brought in 

 abundance by the rills, brooks, and rivers that flowed down from the waning ice- 

 sheet, was very probably fivefold to tenfold more than now. Under these con- 

 ditions of very abundant silt, rivers swollen to floods throughout the summers, 

 and less current of their sluggish descent to the Gulf, it is estimated that the lowan 

 stage of chief deposition of the valley loess, gradually building up the river flood- 

 plains to heights of 150 to 250 feet above the bottomlands of today, may have occu- 

 pied only about a thousand years. 



During the same time the winds are thought to have blown away mucli of the 

 loess from the valley floodplains, and from the ice surface, spreading it far and wide 

 as the general sheet of upland loess, mostly 10 to 25 feet thick, mantling the high 

 and low lands upon the great areas between the rivers with a surprising uniformity 

 of thickness. It is evident also that this silt mantle includes some contribution, 

 most considerable westward, of wind-borne dust from the great western plains, 

 this part being not of glacial origin. 



Alter the accumulation of the loess, and before the moraine-forming Wisconsin 

 stage of the waning and wavering glaciation, this region was uplifted 300 to 500 

 feet, or perhaps somewhat more, on account of the diminution of the ice weight 

 and pressure, thereby giving to the rivers the same steeper gradients and more 

 powerful currents as now. They therefore eroded the valley loess to depths some- 

 what below the present bottomlands, and sculptured the valleys in nearly their 

 present forms, with high inclosing bluffs of loess, before the moraines of Wisconsin, 

 Minnesota, and northern Iowa were amassed along the ice boundary at pauses of 

 its general retreat. 



Again, during this Wisconsin stage much modified drift was borne into the val- 

 leys. Its coarser portion of gravel and sand filled the valleys anew to heights of 

 100 to 200 feet, or more, near the ice border ; but the strong river currents, with 

 nearly their present slopes, carried the fine silt, corresponding to the former loess 

 deposit, far down the valleys to the lower Mississippi and the Gulf. 



Along the Big Sioux valley, on the northwest boundary of Iowa, a floodplain 



LXXVII— Bum,. Geoi,. Soc. Am.. Vol. 14, 1902 



