Uncovering the Past


As the work day begins at Yat Kitischee, a two-person archaeology team begins work in a new excavation square, its perimeter outlined by white string pulled taut between wooden stakes in each of the square’s four corners. Nearly a hundred other stakes stand erect in neat rows, each stake exactly two meters apart. The stakes are part of the grid system.

Other archaeologists set up the transit and unload tools from the trucks. A few of the volunteers who spent the evening sharpening their trowels climb into open squares to pick up work where they left off yesterday. The crew chief stops and gives instructions for drawing a profile that will show the various soil layers. They disappear into the square to clip roots and shave the walls of the excavated square straight with their sharpened trowels. Coffee steams out of styrofoam cups set in wheel barrows, and bug spray mist chases the mosquitoes back into the dense brazilian pepper.

Back in the new excavation square, the archaeologists use rope to suspend a screen from a large saw-horse-like stand located near the edge of the square, and then move a wheelbarrow underneath to catch the sifted soil. The crew chief squints through the barrel of the transit, peering at a tall, white stadia rod with black and red numbers that one of the crew steadies next to a corner stake. As the crew chief calls out elevations, a second crew member records them on a sheet of paper attached to a clipboard. These elevations will enable the archaeologists to record the exact depth of each artifact and feature they find in this square.

The surface of the unit is nearly level and the crew begins digging. One person carefully scrapes away the soil with a flat shovel, tossing the soil into the screen with a casual accuracy that comes from years of experience. She is dressed in shorts and a loose tee-shirt, and wears flat-soled boots to protect the unit’s floor. Her partner shakes the screen back and forth, barely altering the steady, rhythmic motion to catch the flying clumps of soil. Artifacts, food bone, and shell quickly collect in the screen as the wheelbarrow underneath fills up with a rich dark soil.

Midway through the level the digger notices a circular stain in one corner of the unit. She stops digging, bends down, and carefully scrapes soil away with her trowel. Her partner uses this lull to stop shaking and begin picking broken pot sherds, fragments of bone and shell, and an occasional chert flake out of the screen. "What is it?" he asks, glancing over to her kneeling figure. "Looks like another post," she answers. He places the artifacts he has collected in a plastic bag and walks over to his tool box, grabbing a ruler and clipboard. "Bring the plumb bob," she asks.

Together they draw a map showing the stain’s shape, measure its location, and record its content. The elevation of the feature is recorded with the transit before they consult the master list of identified features in the crew chief’s notebook. This stain will be designated Feature 25—a possible post mold. A large map showing all of the excavated features is spread out on the table by the truck. They look for their square, 908N/914E, and note that Feature 25 and five other post molds in an adjacent square, form a semi-circle indicating the outline of a possible structure.

They walk back to their square and continue digging in all areas of the unit except the stain, which will be removed separately so any differences in artifacts, shell, or soil can be noted. The floor of the square is excavated down one level, or exactly ten centimeters, and the digging stops. The artifacts are sorted and counted. Separate bags are made for the ceramics, bone, lithics, and shell tools. The leftover shell is placed in five-gallon buckets and weighed. Notes are taken. "The recovered sherds all appear rather small in size and are perhaps the result of being walked on and broken, indicating that this area might have once been a living floor," begins the comments. Soil color, shell density, and artifact counts are added to the notes. The team carries the buckets of weighed shell to the edge of the clearing and dumps them on a pile that grows larger every day. From the pile, they can see airplanes landing at nearby St. Petersburg-Clearwater International Airport. An osprey carries a mullet it has caught back to a nearby nest. On the way back to their square, they walk past other crew members getting a completed square ready for photographs and past a volunteer brushing off a pot sherd. In the background they overhear a school group getting a tour of the site. The sun has risen over the tree tops and sweat drips freely off their foreheads. The two archaeologists take a brief break, getting a drink of water and putting on sunscreen before they switch places and begin another level.

W hen people visit an excavation in progress, they typically ask a lot of questions.
In the following pages, we attempt to answer some of the most common ones.

How deep do you go?

Once archaeologists begin to dig, they like to keep digging until they reach sterile soil, or in other words, until there are no more artifacts or features. And even then they don’t stop! It is considered good practice to dig several sterile levels without finding anything whatsoever! This way they can be sure that they are not missing an earlier occupation that may be separated from later occupations by sterile soil.

What are you looking for?

More than artifacts, archaeologists are looking for clues that can help them interpret the past. These clues may consist of physical evidence such as pot sherds or shell tools, although more often they consist of animal bones, plant remains, stains in the soil, or even the chemical composition of the soil. Even more important, however, are the vertical and horizontal relationships of the physical remains. Searching for, recording, and interpreting these clues makes archaeology a lot like detective work. And it is why you will see archaeologists spending a lot of time drawing maps, measuring the locations of their finds, and writing notes, perhaps even more time than they spend digging.

Post Molds
Prehistoric houses and other structures were usually made of wood. A basic construction technique involved placing support posts in the ground to create a frame, and then using other materials (branches, palm fronds, more posts, etc.) to enclose the structure. When the wooden posts deteriorate or burn they leave a stain in the soil that indicates where the original posts were located. These stains are called "post molds" and the holes that were dug to place the posts in are called "post holes". Post molds and post holes are often arranged in a pattern that indicates the structure’s size and shape. At Yat Kitischee, thirty-three post molds were identified during excavation. By themselves, each post mold appears insignificant. But when several post molds are exposed and mapped, the patterns of early structures are revealed. Sometimes wood or charcoal from the original post will be found in a post mold, and by using radiocarbon dating, the archaeologists can determine how long ago the wood for the household was cut.

Stratigraphy
The study of the various strata, or layers of soil, at a site is known as "stratigraphy". Archaeologists are interested in stratigraphy because each layer represents a different period of soil deposition, and distinct strata can be used as markers to separate the different occupations of a site. The different layers are recorded on profile drawings which are used by the archaeologists to interpret the developmental history of the site. For example, at Yat Kitischee four distinct strata were observable and each was related to a different period of site use. Common sense tells us that the deeper an object lies below the surface, the older it is. This basic principle, known as the law of superposition, is the basis for interpreting stratigraphic profiles. Thus, the lowest strata at Yat Kitischee represents the earliest occupation of the site, and the highest strata represents the most recent. In between there was a layer that consisted of many individual deposits of food refuse that accumulated during a period when part of the site was used for trash disposal.  Below this, and above the earliest layer, was another occupation zone that contained many post molds and features.

Why dig square holes?

Archaeologists are very concerned with context, or the horizontal and vertical relationships between artifacts and features. These relationships reveal patterns that are important for interpreting a site and understanding how people lived. The horizontal dimension reflects spatial patterns and the vertical dimension reflects temporal patterns. Square holes are one way that archaeologists are able to maintain and record the context of their finds. They are usually of a standard size (at Yat Kitischee the archaeologists used squares that measured two meters, or about six feet, on a side) and the corners of each unit are tied into a grid system that enables the archaeologists to know precisely where they are within the site. The straight walls are useful for accurately measuring the horizontal position of any artifacts or features found. They also offer four views of the stratification within a site.

Great care is taken so that each excavation unit remains square and that all measurements are accurately made. Archaeologists know that they will have the opportunity to excavate a unit only once. After they finish, what was contained in the ground, the context of the artifacts and features, is gone forever, so archaeologists are careful to notice and record everything they can.

 

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