DAACS Seriation Method
DAACS staff developed a frequency-seriation based chronology for the Building o site (see Neiman, Galle, and Wheeler 2003 for technical details). DAACS seriated ceramic assemblages, with more than five 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 o, two portions of a single layer, described by the excavators as “orange clay with greenstone,” spanned two adjacent quadrats (536 and 537). The two layer segments were excavated as 536C and 537B. DAACS assigned these contexts to a single stratigraphic group (SG13). Not all contexts have stratigraphic group assignments.
DAACS chose to base the seriation chronology for the Building o 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 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 o Site Phases
Based on the correspondence analysis, DAACS divided the Building o site occupation into five phases. Mean ceramic dates for the five Building o phases are given in the table below. The table also includes two estimates of the 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-types. This TPQ estimate is more robust against excavation errors and taphonomic processes that might have introduces a few anomalously late sherds in an assemblage.
The phases are massively time averaged. This is the result of both site formation processes and excavation and analytical errors, which may have combined, in a single context or stratigraphic group, deposits from different time periods. Each phase represents deposition over many decades and there is considerable overlap between the periods represented by successive phases.
Phase 1 includes a pit (F10, SG04) dug into a buried-A horizon (SG10) that the excavators referred to as "the occupation zone." Although there were no artifacts associated with it, the southeast-corner foundation segment (F01) may also date to Phase 1. Phase 2 is comprised of assemblages from contexts associated with Building o, as described on the 1796 Mutual Assurance Plat for Monticello. This structure (FG02) is represented by the southern and western wall segments (F02, F03), the brick paving (F04), and two subfloor pits (F06, F05). Only the larger of the two subfloor pits (F06, SG09) contained a sample of ceramics large enough to be included in the seriation. Most artifacts from Phase 2 occur in the buried-A horizon (SG10) that surrounded these features. Phases 3, 4, and 5 include assemblages from layers that overlay SG10. Phase 3 includes the displaced subsoil (SG13) that was probably excavated upslope in connection with construction of the south dependency wing of Monticello mansion in 1801. Phases 4 and 5 contain significant amounts of post-Jefferson era material.
A Seriation Chronology for the Building o Site
The following table presents a seriation chronology for the Building o site. We use the indefinite article to signify that it is not the only chronology possible, nor even the best one possible.