testing the dirt

When making Adobe or Cob, it is important to know the makeup of the dirt one is using. Today, I tested the soil in three places on my land. One was the excavated material from the foundation ditch. Another was from dirt 3 feet below the ground. And the third sample was taken from a wet weather creek that runs through the property. Mostly, I am searching for the clay content as it is an important ingredient in making cob and mortar. For this test, I followed the instructions from a book called, "The Hand Sculpted House" by Ianto Evans. I filled a glass jar 1/3rd full with the dirt sample, added water to the top and then a teaspoon of soap. I shook up the contents and then let them settle. Whatever settles in the first 5 seconds is coarse sand, also very important. What settles over the next ten minutes is silt, which doesn't have much use. What settles over the next few days, is clay. Clear layers are formed, which makes the result easy to decipher. I'll soon know the clay content.