TJie Upland Loess of Missouri. — Hcrshey. 369 
THE UPLAND LOESS OF MISSOURI — ITS MODE 
OF FORMATION. 
By O. H. Hershet, BrHgdon, California. 
Several years ago professor J. E. Todd, of South Dakota, 
and the writer conducted, through the correspondence depart- 
ment of "Science," a brief discussion of the question of the 
mode of deposition of the sheet of gray loamy clay or "upland" 
loess which mantles the whole of northern Missouri, professor 
Todd maintaining that it was formed under distinctly fluviatile 
conditions, while the present writer was equally certain that 
the m.edium of transportation and deposition of the fine silty 
mziterial was essentially lacustrine or even marine in character. 
It came to an untimely end through my failure to reply to 
professor Todd's third letter. 
It is not my purpose to resume the discussion, but a series 
of observations made last summer during an extended pedes- 
trian trip across Missouri, has thrown new light on the sub- 
ject and seems worthy of record. 
At the close of the Kansas epoch of the Quaternary era, 
nearly the whole of northern Missouri was a remarkably level 
drift plain.* This had a perceptible but very slight slope 
southeastward, southward and southwestward toward the Mis- 
sissippi and Missouri rivers. Had the upland loess been de- 
posited upon this drift-plain before its dissection, the idea that 
the silt was carried r.nd spread over the land by great rivers 
flowing away from the lowan ice-sheet on the north, would be 
tenable. But if there is one fact in the Quaternary geology of 
Missouri which is absolutely certain, it is that a long interval of 
erosion elapsed betw-een the Kansan glaciation and the deposi- 
tion of the lowan loess. This resulted in the formation of 
l)road valleys, seventy-five to one hundred and fifty feet in 
depth, the original drift-plain being thoroughly dissected, and 
remaining only in narrow, widely-separated strips along the 
main divides. Northern Missouri is essentially a hilly coun- 
try. It is characterized by rather elongated but dendritic 
.systems of drainage. These have deeply eroded the old drift- 
plain, and given the country almost as uneven a surface as 
many of the unglaciatcd districts of southern Missouri. 
Upon the old drift soil of this uneven middle Quaternary 
land surface, the u])lan(l loess rests, pretty well mantling the 
