Excavation Methods

Archeologists record spatial information about a site with the aid of maps. Measuring tools range from simple tapes and plumb bobs to laser theodolites. The accuracy of a map is the degree to which a recorded measurement reflects the true value; the precision of the map reflects the consistency with which a measurement can be repeated.

In the course of an excavation, the archeologist carefully evaluates the sequential order that processes such as the collapse of buildings or the digging of pits contribute to the formation of a site. In addition, the archeologist typically notes such details as soil color and texture, and the presence and size of any stones.

The way the research proceeds at the site will depend on the goal of the excavation. If the purpose of the excavation is to document the placement of all retrieved artifacts and fragments for the purpose of piecing broken objects back together, the level of recording field data will be much finer than if the goal is simply to retrieve large objects. In cases where the goal of the site research is, for example, to recover flakes and chips of worked stone, digging at the site typically involves a trowel and whisk broom, and almost always, screening or sifting techniques. One-quarter-inch (6 mm) screens are usually fine enough for the recovery of most bones and artifacts, but finer meshes may be used in the recovery of seeds, small bones, and chipping debris. When a screen is used, shovels full of soil are thrown against or on the screen so that the dirt sifts through it, leaving any artifacts behind.

Another technique frequently utilized in the recovery of artifacts is water-screening. By using a water pump to hose down the material to be screened, the process of recovery is sped up and the loss of objects that might be missed or damaged in the course of being dry-screened can be avoided. A drawback in using this recovery technique is that it generates large quantities of mud that may cause environmental damage if dumped into a stream.

Elaborate flotation techniques may be used to recover artifacts, seeds, small bones, and the remains of charred plant material. In these techniques, debris from the site is placed in a container of pure or chemically treated water. The container is then shaken, causing small objects to float to the surface where they can be recovered. Archeologists have developed elaborate modifications of this technique, some involving multiple trays for the sorting of objects, to facilitate the recovery of artifacts. Many of these artifacts are analyzed under a microscope to look for clues about manufacture and use. The smallest artifacts, microartifacts such as pollen and seeds, require the use of a microscope for simple identification.

Prior to being sent to the laboratory for processing, artifacts are placed in a bag that is labeled with a code indicating where and in which stratigraphic layer the artifacts were found. All relevant information about an artifact is recorded in the field notes for the site.