Science behind Stone Walls

Science behind Stone Walls

Stone walls are ubiquitous in New England, most of us take them for granted, not giving them a second thought, yet there is a rich history regarding these seemingly innocuous structures. The book “Stone by Stone: The Magnificent History of New England’s Stone Walls”, written by University of Connecticut geology professor, Robert Thorson explores the geoarchaeology of stone walls and their winding tale which begins with the last glacial era, wanders through colonial and early New England farming, falls to the wayside during industrialization and finally to today where he advocates for their conservation as important, historical landforms.

Stones used to construct New England's stone walls were removed from bedrock by the retreating Laurentide glacier, 15 to 30,000 years ago.

Stones used to construct New England’s stone walls were removed from bedrock by the retreating Laurentide glacier, 15 to 30,000 years ago.

According to Thorson, New England’s stone walls originated from the retreating Laurentide ice sheet, approximately 15 to 30,000 years ago. The glacier’s retreat stripped the remnants of ancient soils, leaving bare bedrock, lifting and scattering great stone slabs about the region. The melting and receding of the ice sheet deposited a range of geological materials ranging from clay to huge boulders broken from slate, schist, granite, gneiss and bedrock. It also helped form the rich soil comprising New England’s rolling hills and meadows; “lodgement till”, 60 meters thick in places. Just above the lodgement till was a thinner, looser layer of rocks and sand, called “ablation”, mostly the stones comprising ablation were large, angular, abundant and easy to carry. Stone walls in New England are comprised, for the most part, of rocks from the ablation.

Although popularly thought of as being constructed during the colonial era, inhabitants of that time used rail fencing to pen animals, while stone walls were not built until the latter half of the 18th century. Pioneers clear-cutting New England’s forests from 1830 to 1880 would find stones buried deeply, under thousands of years of composted soils and old growth forests.

Deforestation produced by clear-cutting to build houses and heat houses and farm exposed soils to extremely cold temperatures, colonization coincided with the “Little Ice Age”, the unusually cool climatic period that lasted from the mid-1300s to the mid-1800s. Keeping New England farmhouses warm used about 35 cords of wood per year. Newly exposed soils froze deeper than they had previously, accelerating frost heaving and gradually lifting up billions of stones through soil layers, bringing them to the surface. Stone were not conducive to farming, so farmers used oxen to move them to the outer edges of their property, basically dumping them into piles which delineated their property from the forest. Later these piles would be arranged with more intention to form the stone walls we know today.

Stone walls were abandoned along with farmland when New England farmers moved west.

Stone walls were abandoned along with farmland when New England farmers moved west.

The oldest stone wall in New England, found north of Portland, ME along the estuary of the Kennebec River, dates back to 1607. However, Thorson terms the period between 1725 to 1825 “The golden age of stone wall building”. During this period thousands of stone walls were built and more were repaired. Over the next couple of generations, through painstaking, back-breaking labor, New England’s network of stone walls was constructed. By the 1830s to 1840s farms were effectively established, so most of the land clearing activities cam to a halt. Farming techniques were improving, new tools and methodologies were implemented with great success, but the so-called “volcanic winter” of 1816 forced many farmers to abandon their lands. Mount Tambora in Indonesia erupted in 1815 ejecting ash and particulates into the global atmosphere, crops were devastated. Between the loss of a year’s worth of crops and the impending industrial depression New Englanders felt the answer lay west, and moved to New York, Chicago and beyond. The exodus lay fields fallow and allowed stone walls to become overgrown with unchecked vegetation.

The Journal of Archaeological Science published an article in March 2014 talks about fascinating research into what currently lies beneath the forests that grew and replaced abandoned farmland. University of Connecticut geographers Katharine Johnson and William Ouimet are using LiDAR technology for aerial surveys of heavily forested areas in three southern New England towns. Remnants of the former agropolis were found, networks of roads and stone walls which have been buried beneath dense forests for centuries. Thorson’s stonewall initiative, through the Connecticut Museum of Natural History (http://www.cac.uconn.edu/mnhhome.html), aims to ensure that stone walls, “New England’s iconic landform”, remain in place for generations to come.