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Cob: blue clayTim Kring tkring at mindspring.comSun Apr 28 10:47:12 CDT 2002
The blue or gray clay is commonly due to reduction of iron in the soil. This is a normal part of soil formation. ( I am speaking primarily of the soils here in Georgia , Ultisols formed in coastal plain marine sediments (Where Pat Newberry lives) and Piedmont material forming from Granite/ acid crystalline rock formations. Think of the soil as being a neutral to gray in color to start with. You could think of it like the color of sheet rock. Because of the huge amounts of iron (red color) and other minerals in the soil, the dirt will have a reddish, brown or yellow hue or color. During saturated periods, the soil microbes (bugs) will consume the oxygen out of the soil water. When this oxygen has been used up, they will basically utilize /strip the iron off the soil particles or peds themselves. Once this iron has become mobile due to reduction, it washes out as the water table moves down and out of the soil profile. The soil no longer has its red color which has now been removed, the remaining color is the soil color gray or blue. This is sort of like stripping the red wall paper off of the sheet rock. You can fist see the signs of this as you dig down into the ground on a transitional position on the landscape, the deeper you get, the more gray spots or mottles you may find depending on how the site is draining. A lot of water moves laterally in the ground not just strait down. If it didn't, there would be not creeks and they certainly wouldn't be flowing during dry periods. By the time you move down the hill or side slope to a creek and or flood plain position, the soils may be very gray in and around such bottom land areas. Frequently, you may have to dig down somewhat, due to frequently deposited organic matter that is in the surface layers, or depth of water table. Tim in Georgia
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