Topography of Hozi'ard Co., la. — Calvin. 377 
cut in the recently deposited loess, but in general the amount 
of erosion since the loess was laid down as a comparatively 
thin mantle over the trenched surface of ancient Kansan, is sq 
small as to be scarcely appreciable. For a measure of the 
amount of erosion that has taken place since the period of loess 
deposition we may turn to the lowan plain, for in the matter of 
age the lowan drift is contemporaneous with the main body 
of the loess of this part of the Mississippi valley. The fact is, 
that with very few and very unimportant exceptions, 'the sur- 
face of the younger drift remains practically as the glaciers 
left it. Over ninety-nine per cent, of its area and more, the 
erosion of the surface, from the withdrawal of the lowan ice to 
the occupation and cultivation of the territory by the white 
man, would have to be expressed by zero. Except in some 
trifling and unimportant details, therefore, the topography of 
the Loess-Kansan region is not due to erosion of the loess, 
but is controlled by surface forms which had been developed 
long before any loess was deposited. All deep cuts for roads 
or railways or for whatever purpose made, in Loess-Kansan 
areas of Iowa, whether in Howard county or in other portions 
of the state, show that the present loess surface is essentially 
parallel with the old eroded surface of the Kansan till. xA^t 
the risk of seeming to indulge in unnecessary reiteration it 
may be stated tliat all field evidence is overwhelminglv in 
favor of the view that the topography of Loess-Kansan areas 
— such topography as is shown in figure i — is fundamentally 
pre-loe^sial. The loess did not level up the surface as some 
have supposed. Over the greater part of the area in which 
it is distributed it has not been eroded to any appreciable ex- 
tent since it was laid down. Its thickness and general rela- 
tions to the surface have never been very different from what 
'they are to-day. 
A marked departure from the type of topography gener- 
ally prevailing i^i the Loess-Kansan area of Howard county 
is found in the charmingly picturesque valley of the U])per 
Iowa or Oneota river. This valley is a deep trench cut into 
the indurated rocks.. In some of its characteristics it resembles 
the valleys of the Driftless Area. The topography of the 
greater part of the northeastern division of Howard county 
is post-Kansan in age. It was developed, as already noted, 
