They are often very interested in the structure of the soil itself. It can give clues as to whether the buried portions of the site have been disturbed and tell, through the use of the principles of stratigraphy, how old things are and when they were buried. Special maps of the sides of excavations units are called profiles. Profiles help show the different layers of soil and the location of some of the artifacts. These are the fundamentals of archaeological excavation.
Many archaeologists consider excavation more of an art than an exact science.
When you're out in the field conditions are always different and experienced excavators are what keep many a project from going awry. Most people attend archaeological field schools to learn the basics and then spend several seasons brushing up on their skills. Archaeologists don't just go out and start digging, there's a lot of preparation, planning and learning involved before they every move a single clod of dirt. Click HERE to see a short movie of a Historic archaeological site in Central Texas, where archaeologists are uncovering the remains of a grist mill, during full blown excavation.