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March 7, 1997:
Further Mysteries of the Mud Mass

Overhead shot of excavation After we have defined the walls and their faces in the muddy surface under the sand in our squares, our next task is to remove the tumble from between the walls. This debris, composed of dislodged bricks, wind-blown sand, some broken pots and collapsed plaster, is often difficult to differentiate from the material which makes up the walls themselves. However, once it is exposed to the sun and dries out a little, the random patterns of loose bricks and short, broken lines of plaster become clear. Working away from the walls we have defined, we begin to remove the tumble in level "passes," paying careful attention to the way bricks and pot sherds lie. At the point where the bricks and pot sherds begin to lie flat, it might be a clue that we are approaching a different level or feature.

Man brushing carefully at partially-buried shards In practice, this seemingly simple operation can be quite difficult. The preserved tops of intact walls are seldom perfectly level. Walls are often covered with tumble and pottery of different thicknesses, so parts of the same structure will be revealed at different times. This is why the excavator has to form hypotheses not only about where walls might be, but which way they run, how thick they are, and where doorways might be found so that more careful work can expose the preserved tops of the architecture. In this way—patiently trowelling in areas where walls are suspected, and more aggressively removing layers known to be tumble—we hope to preserve the remaining mudbrick structures and expose the occupational debris underneath the fallen bricks.

Man washing pieces Another aspect of excavating tumble is how we treat the soil we remove. Ideally, we not only want to save all pot sherds, bone fragments, stone tools, pieces of charcoal and mud sealings we find as we dig, but we also want to sieve all our soil to catch anything we miss. Even after sieving, most of the clumps left over are difficult to sort because they are covered with wet sand and mud. Usually this left over material is "wet sieved," which means that we pour it into a fine screen and gently rinse it with water to clean off all the obcuring sand and mud. What is left is laid out to dry and sorted into bags the following day. This process is time consuming and labor-intensive but its rewards can be great. So, in order to make the best use of our limited time in the field, we will only wet sieve a small portion of the soil we judge to be from collapsed walls. We hope that the time we save here can be better used later to screen the underlying material which was deposited when the building was in use.

In addition to wet sieving, every feature, whether tumble or occupational debris, is sampled for flotation. This means that, periodically during the excavation, we will fill half a sandbag with unsorted, unscreened material from the feature. Later, Mary Anne Murray, our paleobotanist this season, will mix some of this sample with water and run it through a series of finer and finer sieves to collect seeds and other plant and animal remains. We hope that what the largest of her screens strains out (what we call "heavy fraction") will help us check what we might be missing during excavation.

Using these techniques, we hope to clear our walls and rooms down to any floors we might have. Then, with the mysteries of the mud mass behind us, we will see what story our site will reveal this year...

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Photos: Carl Andrews

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