A Date with Dendrochronology

We had something really cool happen at White Plains this summer. We found out the house’s construction date through Dendrochronology. Ever heard of it? I hadn’t either until our friends at the Fairfield Foundation and Camille Wells shared this fascinating process with us.

Since we moved to the house at White Plains, there have been so many possible dates offered to define its construction history: Legend places the house’s build date in the 1720s; the Thornley family bible talks about family members born there in 1750; architectural historians have placed it closer to 1815; and yet tax records place it at 1795! In an effort to definitively narrow down its build date, we requested that dendrochronologists William Callahan and Dr. Edward Cook perform a tree-ring analysis of selected structural timbers.

Did I need to know? No. But as someone who likes to know things based on fact, it’s a great feeling. And somehow it allows you to better understand the house within a specific cultural setting, time period, and life cycle in relation to the people who lived here.

Timbers - White Plains
Attic timbers, White Plains

Callahan and Cook describe the process’ history:

Dendrochronology is the science of analyzing and dating annual growth rings in trees.  Its first significant application was in the dating of ancient Indian pueblos of the southwestern United States. Andrew E. Douglass is considered the “father” of dendrochronology, and his numerous early publications concentrated on the application of tree-ring data to archaeological dating.  Douglass established the connection between annual ring width variability and annual climate variability which allows for the precise dating of wood material. The dendrochronological methods first developed by Douglass have evolved and been employed throughout North America, Europe, and much of the temperate forest zones of the globe.

Bill arrived at White Plains in early August for two days of sample collecting to complete the dendrochronological analysis of the timbers. He brought an elaborate, and very well-organized, tool collection that included several bores, all handmade by a famous dendrochronologist in Sweden. 13 samples, all oak, were collected from both the basement and attic timbers using the bores, heavy drills, and lots of patience.

Bill Callahan - Dendrochronology
Bill showing the huge handmade wood bores

The wood samples collected were processed in the Tree-Ring Laboratory, part of the Lamont-Doherty Earth Observatory at Columbia University by Dr. Edward Cook following well-established dendrochronological methods. As described in the final report, “the core samples were carefully glued onto grooved mounts and all were sanded to a high polish to reveal the annual tree rings clearly. The rings widths were measured under a microscope to a precision of ±0.001 mm….A total of 13 oak samples were analyzed in the laboratory, with all 13 samples providing firm dendrochronological dates.”

Bill Callahan - Dendrochronology
Bill drilling a primary beam timber in the basement

The final analysis and report by Callahan and Cook dates the timber cutting and likely construction within a very specific time frame:

Selected timbers of the house strongly indicates a major construction (or renovation) phase for the building beginning in very late 1785 or early 1786. Cutting of the bark-edged timbers occurred … during approximately November to February of 1785 and 1786 respectively. Usage of the materials took place shortly thereafter, for close in situ inspection of the oak timbers indicated that most if not all of the materials were utilized soon after cutting, in keeping with historical woodworking and carpentry techniques. Thus, the specific year of this construction activity is most likely during 1786, perhaps eventually continuing into 1787. The consistency of the datings between elemental locations within the house is noteworthy.

White Plains House
White Plains, 1786

Although the current structure can be dated to 1786, there is no evidence to disprove the theory of an earlier building on the same site. Thornley family stories and writings describe old Aaron Thornley as being born at White Plains in 1750, but it was likely in a different house elsewhere on the property or in an earlier house on the same site, assuming that the family folklore is even accurate. But THIS house can be undeniably dated to 1786, just three years after Aaron Thornley laid out the site plans for Port Conway, VA, making the house at White Plains one of the rare 18th-century buildings in King George County still retaining both its original footprint and historical integrity.


And now we know. I’m so glad that we took this opportunity while we had the chance. Bill was fantastic to work with and we, perhaps regrettably, gave him the unique cultural experience that is Horne’s restaurant. Oh, Bill… next time we promise to take you somewhere with more than one beer option!

Although too many to list, here are some of other regional dendrochronological projects that you may know, also completed by Callahan and Cook:

Gadsby’s Tavern, Alexandria, VA
Hanover Tavern, Hanover Courthouse, VA
Independence Hall, Philadelphia, PA
Marmion, King George County, VA
Menokin, Richmond County, VA
Sabine Hall, Richmond County, VA
Shirley, Charles County, VA
Wilton, Westmoreland County, VA

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