The Geology of Colonial New England Stone Walls
BY COREY SCHWEIZER
The stone walls that are found throughout New England are some of the most important and beautiful walls ever built. These walls were used for anything from animal pounds, to boundary lines to animal fencing. In the nineteenth century, when a stone wall was finished it needed to be inspected by a fence viewer. A fence viewer was a municipal worker that would inspect fences to make sure that they are structurally sound.
If a stone wall was deemed sound, then the owner was not liable for damage done to his crops by other farmer's animals.
As farming grew more popular in New England, the need for adequate fencing also increased. Before stone walls were widely used, wooden rail and zig-zag fences were the practical solution for fencing in a farm. This quickly became a problem because once the land was cleared for a farm, few trees were left to build the wooden fences. The wooden rail fences would also rot over time and need to be replaced. Farmers soon switched to using rock in their fences to replace the old rail and zig-zag fences and to make use of stone found in their farm. By 1871 approximately one-third of the 61,515 miles of fencing in Connecticut were stone. 
Once the act of making fencing out of stone became the standard in New England, farmers were faced with the problem of obtaining the stone. Some farmers could build a wall with stone that was found on their farmland. Most farmers however, had to steal or buy the stone. Farmers could also hire stonemasons to build the wall. "Some experienced stonemasons were paid as much as $3.50 for 10 hours of work, while un-experienced stone masons were paid up to 1.25 an hour". 
The period from 1775 - 1825 was known as the golden age of stone wall building. During this time period, more stone walls were built than any other period of time. This period of time was also when more and better designed stone walls started to take the place of older stone walls. The increase of stone wall building during this period of time is due to a few factors. The main reason for the increase was directly linked to an increased interest in farming in New England. The increase in stone wall building from 1775-1825 is also the direct result of population increase. New advances in travel and farming allowed stone walls to be built faster.
The type of rocks that masons used to build stone walls in New England varied. Most of the time the rocks that were used in a wall were granite, limestone or gneiss. These rocks were the most popular to use because they were found in abundance across New England. These are also the few types of rocks found in New England. When a mason or a farmer requested rocks, they usually had to be drilled or mined out of caves. A substantial amount of rocks used in stone walls were also those found in farms and in woods.
The reason why so many stones were found throughout farms and woods is because of glaciers. When the glaciers were formed, they trapped many rocks within them. When the glaciers melted across New England, they would dump millions of tons of rocks in random places such as woods or land that would be used as farm later on. The only types of rocks that could survive a glacier are the really hard ones, such as granite and gneiss.  Glaciers also left many fieldstones and other rocks rather smooth because a glacier would tumble and tend to smooth out many rocks. Because of the round shape of these rocks, they were not very useful in building walls. The rocks that were not rounded however, were very hard and durable once put in a wall.
Granite is the most common rock found throughout New England. Granite is extremely hard and did not smooth out easily, which made it the optimum rock of choice with which to build walls. There are three categories out of which a rock could fall under: igneous, metamorphic and sedimentary. Granite falls under the both the igneous and metamorphic class of rocks. Igneous rocks are formed by the cooling and hardening of magma found within the earth. As the magma cools, most rocks will already be hardened or crystallized. The last rocks to crystallize are potassium feldspar, muscovite mica, and quartz, which are the major components of granite. 
Rocks also fall under the categories of acidic, intermediate or basic. Metamorphic rocks are formed under particular temperature, pressure, and chemical conditions that produce rocks with different textures and minerals. These rocks are formed under the earth's surface by great stress and high temperatures. 
Granites show evidence of both the igneous and metamorphic processes. Some granite has a crystallized melt form, which is found only in the igneous process. Other granites however, show evidence that they were formed through the metamorphic process. The metamorphism of a granite rock is called granizitation. 
Gneiss is another important rock used in building stone walls. Gneiss is similar to granite in that it is formed through the metamorphic process, and that it can survive a glacier. Gneiss is different in other ways. Gneiss is formed by the magma in the earth heating up as opposed to granite, where it is formed by magma cooling down.  Gneiss is a coarse rock and is usually not very smooth. Gneiss is also a rock with very distinct banding, usually of light and dark layers, and forms when the atoms of minerals break down chemically, segregating into different layers, each of which with its own distinct mineralogy. 
Limestone is another metamorphic rock found in the building of stone walls. Limestone is an extremely basic type of rock that is found in few stone walls. Most limestone found in a stone wall is used as mortar or is put in accidentally after being mistakenly identified as granite or gneiss. It is rather brittle and is not very useful. "Limestone consists of consolidated carbonate muds precipitated from seawater or of carbonate skeletal remains of marine organisms". 
The third type of rocks are sedimentary. Sedimentary rocks tend to be created by weathering from the elements. Sedimentary rocks are formed by the heating of magma in the earth, weathering from wind and water, and breakdown caused by intense pressure from the earth. Sedimentary rocks tend to be rather brittle because of all the weathering they have endured.  Because of this, most sedimentary rocks are not very helpful when building a stone wall. Gravel is one of the few sedimentary rocks that are helpful in building a stone wall. Gravel can be placed under a stone wall in a trench to prevent the wall from easily moving or sinking. 
Once the materials necessary to build a stone wall are in place, the building of the wall can begin. Rocks are placed usually with the largest ones at the bottom and using the method of "one on two and two on one". This method means putting two smaller rocks in between two larger rocks and vice-versa to stabilize the wall.
Throughout the farming centuries in New England, many farmers would find that their farmland would have many stones on it that weren't there previously. Before a farmer plowed a farm, there were probably few rocks scattered throughout the farm. When a farm is plowed however, it causes layers of soil beneath the surface to push up their rocks from different soil layers to another.  Eventually, the soil would run out and the rocks would be forced out of the soil and into the farmland. This problem was especially evident in New England because of its rocky and stone filled soil. Many farmers would have to remove the rocks on their farm if they wanted to plow it again, only to find that they would have to repeat the process of removing stones. Many farmers either sold this stone found on their farm or put it into their own stone walls.
Throughout the centuries of farming in New England,
stone walls played an important role. Stone walls were more than
just the mere decoration that they serve today. Stone walls were
used as fencing, property lines, and animal pounds. Most stone walls
today are unnecessary as fencing and have become a sign of wealth.
Stone walls are an important part of history that should not be
 Ibid. 165.
 Ibid. 66.
Charles A. Rocks and Minerals. (New York: Golden Press, 1973)
 Ibid. 7
 Ibid. 8
 Ibid. 10
 Robert M. Thorson. Stone by Stone. (New York: Walker and Company, 2002) 31.
 Chet Raymo, and Mareen E. Raymo Written in Stone. (Connecticut: The Globe Pequot Press, 1989) 26.
 Sorell, Charles A. Rocks and minerals (New York: Golden Press, 1973) 12
 Kevin Gardner. The Granite Kiss. (New York: Country Man Press, 2003) 169.
 Thorson, Robert. Stone by Stone. (New York: Walker and Company, 2002) 45.