I think we need to remember that it's not just the stuff in the pit which fell into disuse, but the pit itself. Farmers had to redig ice pits, tobacco ordering pits, privies, etc and the old pits had to be filled. The old pits may have collected a lot of garbage over a short period of time simply because farmers were anxious to have a potential hazard filled up. So, old pits became targets for garbage and soil from the new hole, and the appearance of a subassemblage may be an artifact of this fact. Many of the ice pits I have seen are filled with early+ 20 c garbage because there was no new pit dug, so there was no soil from a new hole available to partially or completely fill the old hole. So it's just a hole with mason jars, car parts, bricks, shoes, you name it. Why no new hole? Ice boxes and commercial ice became more reliable and more widely available after the first decades of the 1900s, plus after about 1912 the climate in the Mid Atlantic to upper south got too warm for ice to be gathered in any significant quantity from farm ponds. Rovner's comment also notes the need to consider how stuff gets into and moves around in an open pit, especially if it is later sealed. A lot of small stuff and organics could work way down in a pit left open for any length of time. In short, my point is that we have to treat the pit as an artifact with a context before we can understand the artifacts that went into it.