Draw four irregular, horizontal areas on a piece of paper. Put the letter A on the top, B on the second, C on the third and D on the bottom. Draw a small pit cutting through A and B but stopping in C. You’ve just made your own stratigraphy diagram, complete with deposits, boundaries, and a feature that interrupts other layers.
The point of stratigraphy is to determine the order of deposits and features in a sequence. In general, the deepest deposits were laid down first, and deposits above them came later. This is known as superposition. It gives us a relative, not an absolute date. We know that D is older than C, but we don’t know if either deposit was created 50 or 500 years ago.
Cuts are slightly more complicated because they cut across other deposits. In our sketch, the pit cuts through layers A and B and ends up in C. Therefore, the pit must be younger than both A and B, as well as C. Any fill in the pit was put there after the pit was dug. The cut and the fill might have separate context numbers, since they were created at different times, first, the hole was dug, then, the hole was filled in.
It’s easy for novices to be distracted by the shape or color of a layer, and miss the connections between contexts. A thicker layer isn’t necessarily older than a thinner one, and a dark soil matrix isn’t necessarily a hearth. What matters isn’t which layer is more significant, but what the relative positions of contexts are with respect to each other. Did one sit above another? Below? Against? Through? These connections are what give rise to a sequence.
Read the diagram from the most recent context backwards. Start at the top surface and list all the pits, fills, walls, floors, etc., that relate to it. Carefully follow the boundaries. Keep going down until you get to deposits that weren’t cut by later activity. List each connection in a single sentence: “Context 12 was placed above Context 15,” or “Cut 18 cuts through Context 20.” Don’t jump to interpretations; just observe.
Positions of finds can help establish sequences, but only if the find’s context is secure. A piece of pot within a sealed pit fill is part of the fill, not necessarily part of the adjacent layer. A find placed right at the boundary between two deposits requires special attention because it could have moved either in the excavation process or in the original formation of the site. The coordinates, depths, section drawings, and field notes should all corroborate the find before using it in an interpretation.
Reading a good stratigraphy diagram doesn’t require inventing a complex historical narrative. It simply requires establishing a timeline of events that affected the deposits. Deposit D occurred. Deposit C was added above D. A pit was dug, cutting through subsequent deposits. The pit was filled. Once the timeline is established, we can begin to look at artifacts and features in light of that sequence. The easiest way to know when you’re getting better at stratigraphy is when you can follow every boundary in a diagram back to the event that caused it.