DAACS Seriation Method
This page summarizes a frequency-seriation based chronology for the Building s site that was developed by DAACS staff (see Neiman, Galle, and Wheeler 2003 for technical details). DAACS seriated ceramic assemblages, with more than 5 sherds, from individual excavated contexts and from stratigraphic groups -- groups of contexts that field records indicate were part of a single stratigraphic layer or deposit. DAACS assigned such contexts to the same stratigraphic group. Stratigraphic groups have a SG-prefix, which precedes the group number (e.g. SG01 equals Stratigraphic Group 1). For example, at Building s, a single deposit, interpreted by the excavators as “occupation zone east of structure s”, spanned 3 adjacent quadrats (827, 828, and 839). This zone was excavated in 10 contexts (827C1, 827C2, 827C3, 827C4, 828D1, 828D2, 828D3, 828D4, 839B1, and 839B2). DAACS assigned these contexts to a single stratigraphic group (SG10). Not all contexts have stratigraphic group assignments.
DAACS chose to base the seriation chronology for the Building s site on ceramic assemblages aggregated at the level of contexts and stratigraphic groups, and not at the level of features. This is because most contexts and stratigraphic groups on the site were not parts of features. For the relatively few cases where seriated contexts and stratigraphic groups were parts of features, the relevant feature numbers and descriptions are included in the seriation chronology table below.
DAACS computed the frequency of mean-ceramic-date (MCD) types in each stratigraphic group and each individual context that had no stratigraphic group assignment. The seriation chronology is derived from a correspondence analysis of these MCD-type frequencies. Seriated stratigraphic groups and contexts were assigned to 4 phases. Phases are groups of assemblages that have similar correspondence-analysis scores and are therefore inferred to be broadly contemporary. Phases assigned by DAACS have a P-prefix that precedes the phase number (e.g. P01 equals Phase 1).
The stratigraphic relationships among stratigraphic groups and unassigned contexts are summarized in the Harris Matrix for the site. Phase assignments from the seriation are shown on the Harris Matrix in color, facilitating comparison of the seriation chronology and the stratigraphic chronology of the site.
Building s Site Phases
Based on the correspondence analysis, DAACS divided the Building s site occupation into 4 phases. Mean ceramic dates for the 4 phases are given in the table below. The table also includes two estimates of the ceramic TPQ for each phase. The first TPQ estimate is the usual one – the maximum beginning manufacturing date among all the MCD types in the assemblage. The second estimate -- TPQp90 -- is the 90th percentile of the beginning manufacturing dates among all the shreds in the assemblage, based on their MCD-type. This second TPQ estimate is more robust against excavation errors and taphonomic processes that might have introduces a few anomalously late sherds in an assemblage. As the table reveals, all 4 phases at Building s contain post-Jefferson material (note the 1840 TPQ’s for all phases). But the mean ceramic date and TPQp90 estimates indicate the first three phases are dominated by Jefferson-era material.
Phase 1, which contains the majority of the material at the site, represents the early occupation of Building s, as shown as the Mutual Assurance Plat of 1796. The stratigraphic groups assigned to this phase include fill layers (SG01, SG02, SG03, SG04) in the small subfloor pit (F01) beneath Building s. One of the postholes (F15) associated with construction of a parking lot fence in the 1930’s yielded a small assemblage that fell in Phase 1. Phases 2 and 3 are comprised of successively later assemblages to which Jefferson-era occupation was the most important contributor. Only two assemblages from features were assigned to these phases. The assemblage from a second posthole associated with the 1930’s fence line (F16) fell in Phase 2, while the assemblage from a ditch at the northern edge of the site (F04) fell in Phase 3. Phase 4 is dominated by post-Jefferson deposition, perhaps associated with the later Brick Pier Structure (FG05: F22,F23) that sits on the western edge of the site and extends onto the adjacent Building r site.
A Seriation Chronology for the Building s Site
The following table presents a seriation chronology for the Building s site. We use the indefinite article to signify that it is not the only chronology possible, nor the best. DAACS encourages users of Archive data to help explore improvements.