April 11, 2025
This work builds on previous micromorphology studies at Site 30. Check out O'Connor and Neiman 2024 if you haven't already!
Beneath what appeared to be three simple layers of reddish clay in a small cellar at Site 30, a domestic site that was home to enslaved agricultural workers at Monticello in the late eighteenth century, lies an unexpected story of changing household practices. Using micromorphology—the microscopic analysis of blocks of sediment—we've uncovered evidence that residents initially cooked and ate in their house but later shifted to preparing and consuming food with the residents of a second house on the site, helping explain the puzzling scarcity of ceramics associated with the cellar and the house that stood over it.
Figure 1. Field Research Manager Crystal O’Connor admires the cross-section through the small cellar or subfloor pit. The three layers are well defined on the left half of the section adjacent to the one-foot scale, The square cut into the section on the right of the scale was made to take sediment samples for pollen and phytolith analysis (Photo by Monticello Department of Archaeology).
Stratigraphic excavation has long been essential to archaeologists' ability to decipher bits of history lost to time. Traditionally, archaeologists have relied on the macroscopically visible characteristics of sediments like color and texture to distinguish individual layers in the field and to excavate them and the artifacts they contain separately. However, over the past several decades, archaeologists have begun to recognize that layers themselves contain far more information than we can observe with the naked eye and feel at the trowel's edge. Getting access to it depends on adapting methods developed in geology and soil science. One of the most useful is micromorphology.
Micromorphology is the microscopic study of the composition, orientation, and arrangement of fine-grained sediment and larger inclusions in their original positions in the ground. To make that possible, we map and then carefully remove intact blocks of sediment from a stratigraphic section, making sure that the blocks include the interfaces between visible layers. We then impregnate each block with acrylic and grind it down to a translucent slab a few hundredths of a millimeter thick. Studying these thin sections under a petrographic microscope reveals clues to the human activities and natural processes responsible for the deposit and post-depositional alterations to it.
Last November, we began a collaboration with Howard Cyr, a geoarchaeologist who specializes in micromorphology. Our goal is to use micromorphology to advance our understanding of the lives of enslaved agricultural laborers who lived at a spot we call Site 30, about a third of a mile east of Jefferson's mountaintop mansion. Our work at Site 30 is part of the Monticello Household Archaeology Project, our long-term research initiative designed to chart and explain change in household and community organization on Monticello Plantation in the eighteenth and early-nineteenth centuries.
Based on spatial patterns in the distribution of artifacts across the site, we currently suspect there were at least two and probably three houses on the site in the last quarter of the eighteenth century. So far we have discovered subsurface traces of one of them: a subfloor pit or small cellar, roughly 4 by 5 feet in plan and about 1.4 feet deep. We have excavated half the fill in the cellar, exposing a vertical cross-section in which we could see three layers. All three were comprised of red silty clay. They were distinguished from one another by subtle difference in the shade of red and the abundance of charcoal flecks, and clay daub.
Figure 2. Our measured drawing of the cross section though the layers of fill in the cellar or subfloor pit at Site 30. The drawing show the three major layers that we saw in the field. The numbered rectangles are the locations of micromorphology samples (Image by author).
Based on these differences, we guessed that all three layers represented human-deposited fill. But questions remained. Did the layers accumulate gradually over time or were they deposited all at once? Do they contain clues to the way its residents used the house that stood above the cellar and to the process responsible for its demise?
To answer these questions, Howard carefully carved five block samples from the stratigraphic section. Analysis of the thin sections made from the blocks offers exciting insights into the processes responsible for the formation of the layers.
The bottom block, which included the contact between the natural subsoil floor of the cellar and lowest of the three layers visible to us (Layer 3), yielded the biggest surprise. In our careful inspection of the stratigraphic section, we had missed a layer that Howard could see in the thin section with his petrographic microscope! The layer we missed was rich in fine ash, with tiny bits of bone, seeds, and charcoal flecks. It also contained a few, fine, rounded topsoil "peds." These are aggregates of soil particles derived from A horizon or topsoil outside the house. The peds were tracked in by its residents and fell through the boards covering the cellar. The particles in this layer, unlike the three layers above, had been compacted by downward pressure, likely from storing objects on it and sweeping. The ash points to regular use of the fireplace in the house for cooking, while compaction and the thinness of the layer itself indicate the frequent use and maintenance of the cellar.
Figure 3. Annotated photomicrograph from Howard Cyr showing the microstratigraphic contact between the thin ashy layer at the bottom of the pit that was only visible in the thin section and the lowest layer that we were able to see in the field (layer 3). The dashed red and white line follows the contact. Note the much higher frequency of redeposited topsoil peds (RTP) and redeposited subsoil peds (RSP) in the upper layer (layer 3) (Photo by Howard Cyr).
The next layer up—Layer 3—was the lowest one that was visible to us in the field. It too contained rounded topsoil peds tracked into the house on the feet of its residents and fell through the floor boards. However, these peds were larger and more frequent than the ones in the thin ash layer below. Lower levels of cellar use and maintenance allowed them to accumulate gradually over time, forming a layer thick enough for us to be able to see in the field. The larger ped size indicates less frequent sweeping of the house floor. Charcoal flecks attest that fires continued to be burned in the house, but the lack of ash points to lower frequency of burning and fireplace cleaning. Our current hypothesis is that the house continued to be occupied, but its residents cooked and ate in one of the other houses on the site. This hypothesis receives independent support from the otherwise puzzling dearth of ceramics in and around the cellar.
In the field, we could see that the next layer up—Layer 2—contained more clay and less organic matter than the layer below it (Layer 3). Thanks to micromorphology, we now understand that this visible difference is due to higher frequencies of small, rounded topsoil peds in Layer 3 and higher frequencies of small, rounded subsoil peds in Layer 2. The subsoil is probably derived from a large borrow pit that we recently discovered near the cellar. The site's occupants dug the pit to obtain clay with which to daub log houses and their wooden chimneys, bringing clay subsoil to the surface where it could be picked up on its residents' feet and deposited in their houses.
Layer 2 was the last one deposited when the house was still occupied. Micromorphology revealed the tell-tale signs that after deposition ceased, the now stable surface was exposed to sunlight and rainfall for several years, perhaps a decade. Plants began to grow on it and water began to move clay particles downward through Layer 2 and into Layer 3, initiating incipient A-horizon or topsoil formation. In other words, while it looked to us in the field as though Layer 2 represented a single "event," micromorphology shows it contains evidence for three events: the continued occupation of the house by people who prepared and consumed food elsewhere, the abandonment of the house, and the demise of the structure itself or at least its roof.
Finally, the uppermost layer (Layer 1) seemed in the field to be the most clay-rich of all. Micromorphology confirmed this and revealed that it was comprised of a mix of large, mechanically fractured, angular topsoil and subsoil peds. These characteristics point to a single, rapid event in which people deposited large chunks of dirt, sourced from the surrounding topsoil and subsoil, to completely fill the depression left by the abandoned cellar. The charcoal fragments in this layer that we noted in the field were encapsulated in the topsoil peds, indicating they had been incorporated into the peds before deposition. This pattern differs from the lower layers where charcoal particles also occurred outside peds, indicating their origin inside the house.
The synthesis of traditional stratigraphic excavation with micromorphological analysis offers us exciting new insights into coupled cultural and natural site formation processes. We now understand that behind what appeared as three simple layers in the field lies a more complex story of household and community dynamics, changing patterns of daily life, and site abandonment. The micromorphological evidence from Site 30 demonstrates how members of one household adapted their living arrangements over time, possibly shifting from individual household cooking to shared food preparation and consumption. By looking beyond what is visible to the naked eye, we gain new insights into human stories lost to time.