MADISON COUNTY. 423 
depend very largely on the modification of the drift surfaces and these 
details can, in many cases, be very well explained without any recourse 
to the underlying beds. All of the questions that concern the county, 
whether relating to.its topograply, its soils or its water-supply, con- 
nect themselves with the origin and history of the deep drift-deposits, 
by which its entire surface is now covered. 
DRIFT AND SOILS. 
The subject of the Drift has been taken lup so many times, and from so 
many points of view in the reports of the survey already published, that 
it is unnecessary here to treat of it from a general or theoretical point of 
view. 
The deposits of the Drift in Madison county fall under the ordinary 
heads. The lowest and oldest of these deposits is a heavy bed of bowlder 
clay, which covers the face of the country universally. It is a tough, 
waxy, “dark-blue clay, in which scratched and striated pebbles and 
bowlders are abundantly distributed, and occasional seams of sand and 
gravel, varying in thickness from one inch to two feet are found, but 
without regularity or constancy. 
This member of the drift series exceeds the rest very largely in volume 
and also in the importance of its offices. As has been before stated, 
borings of 60 feet are sometimes made without exhausting the bowlder 
clay. These facts seem to indicate that the average thickness of this 
member of the series is not less, certainly, than 60 feet. 
In considerable areas of the county, the bowlder clay forms the present 
surface, or rather the bowlder clay as modified by the action of the atmos- 
phere and of vegetable growth and other organic agencies, upon it. These 
areas constitute the coldest and most intractable lands of the county. 
The soil formed from their weathered surfaces is a black clay one foot or 
a foot and a half in thickness. The action of the atmosphere is shown to 
have reached below the surface in the conversion of one or two additional 
feet of the blue clay into yellow clay. These weathered deposits pass by 
insensible gradations into the underlying deposit. The lands of this 
description are less varied in the natural forest growth than the other 
lands of the county. They are susceptible, however, of considerable 
amelioration by underdraining, and possess all the elements necessary for 
long continued productiveness. 
By far the larger part of the county is covered with another order of 
drift-deposit, viz., those that have been modified and re-arranged 
during a period of submergence to which the original beds have been 
subjected. Ifa bed of the yellow clay already spoken of as formed from 
