—Salisbury is home to the highest elevation in Connecticut on the south shoulder of Mt. Frisell at 2,380 feet and also the highest peak on Bear Mt. At 2,316 feet. It is difficult to conceive that the Taconic hills were once as high as parts of the highest mountains on earth, but millions of years ago they were.

Over millenia the forces of erosion and glacial scraping have formed what we now see as our beautiful landscape. Some of the oldest rock in Connecticut is exposed on the hills around Mt. Riga.

Basis for the following is from “Geological History of Salisbury” was written by Mr. Edward Kirby.

The geologic history of any locality cannot be separated from the surrounding region, the geologic events of the continent or even the total planet Earth. For that reason one must view not only the geology of Salisbury, but that of the surrounding area as well.

The crust of the planet Earth in any area is composed of bedrock formations ranging in thickness from five to twenty-five miles. Bedrock formations in Salisbury are very old. The basement bedrock, Precambrian Housatonic massif, formed about 1.2 billion years before the present (y.b.p.), was developed when proto-North America was in its formative stages and still located in the southern hemisphere. The Walloomsac schist, Salisbury’s youngest rock formation, was deposited about 470 million y.b.p. As the Taconic Orogeny was beginning. This orogeny (mountain building event) resulted in the lifting of the Taconic Range into peaks over 20,000 feet in height and changed all of the local bedrock.

Subjected to intense pressure and heat, the sediments of sand, lime and mud became sandstone, limestone and shale. At that point the Stockbridge formation would have contained numerous marine fossils.

As the Taconic Orogeny continued, thrust sheets over-rode the sedimentary rock formations, causing folding and metamorphism. Local rocks were then gradually changed; granite to gneiss, sandstone to quartzite, limestone to marble and shale to slate, phyllite and schist. The intense heat and pressure changed the nature of the Stockbridge formation to the point where fossil shells would no longer be visible. From the east (eighteen to twenty-five miles) the Everett formation was shove over the region and atop the Walloomsac along a low-angle thrust fault. As a result the tops of Salisbury’s highest bedrock are formed of Everett schist..

As a result of these mountain building events the rocks of this town were changed from igneous and sedimentary to the metamorphic class. During the later Acadian Orogeny some 360 million y.b.p., Salisbury’s bedrock was brought to its current stage of metamorphism. Except for massive erosion as the 20,000 foot peaks were worn away, local bedrock has remained essentially the same for the last 300 million years plus.

In reviewing the sequence of local bedrock, it will be noted locally tht the oldest rocks are not always on the bottom and younger rock do not usually appear on top. Collision between tectonic plates in the earth’s crust has formed an overthrust belt where the basement Housatonic Highlands gneiss has been pushed over the younger rocks in some areas.
Bedrock Geology of Salisbury From youngest (top) to oldest (bottom)
A. Walloomsac formation, Ordovician: schist and limited carbonate rock.
This contact zone between the Salloomsac and Stockbridge formations is the source of world
renowned Salisbury iron ore. The high quality limonite and goethite ores that made Salisbury
famous from 1735 to 1923 were mined in this contact zone at the Ore Hill mines, Chatfield
Mine, Porter Mine, Scoville, Mine and several others along the eastern slopes of the Western
Uplands.
B. Stockbridge formation, Cambrian-Ordovician; source of marble and lime.
C. Dalton formation, Cambrian/Precambrian, quartzite, source of hearthstones for blast furnaces
and building blocks.
D. Everett formation, Cambrian/Precambrian, allocthonous schist.
E. Housatonic massif, Precambrian, basement gneiss.
Glacial Geology
During the Pleistocene Epoch the great Ice Age began about 1.9 million y.b.p. Thick continental glaciers coverd northern Europe, Asia and North America. In North America, the ice radiated out of three major centers in Canada, one of which coverd the region from Hudson’s bay to its terminus at Long Island. While evidence suggests that at least two, probably three, of the Pleistocene advances moved across Salisbury, nearly all observable local glacial features are the result of the comparatively recent Wisconsin stage. Even within each stage there wre smaller advances and retreats. As a result of the ice movements the V-shaped valleys of earlier Pliocene times were gouged to the present day U-shaped valley of the Housatonic and its tributaries.

Far to the north the Wisconsin Stage advance began some 120,000 year ago. The Hudson-Champlain Lobe of the glacier slowly bulldoze through northwest Connecticut and by 21,750 y.b.p. reached its terminus forming the Harbor Hill Moraine on Long Island. The ice cap appears to have maintained its position at this terminus until 18,000 y.b.p. During that period the ice in Salisbury lowlands was probably some 4800 feet, perhaps more, in thickness.

The scouring effect of the moving glacier was tremendous. The mass of ice scraped the land, depressed the bedrock and both rounded and steepened the hills. Rounded hills, U-shaped valleys, kames and kame terraces, glaciolacustrine terraces, glacial striations,

erratics and perched boulders, boulder trains, boulder fields, glacial lakes and multiple proglacial lake beds and other landforms have left a record of major continental glaciation.

Salisbury also has two proglacial lakes, lakes formed in contact zones either against an ice mass or against sediment debris blocking narrow valleys.

These were very large short term water bodies. Proglacial Lake Lime Rock was formed by an ice and debris dam across the Housatonic valley near Kirk Road off Route 7 in Sharon. The main street through Lime Rock Village is on ta glaciolacustrine terrace of the former lake at about 550 feet elevation with the opposite former eastern shore at 550 feet elevation where the Housatonic Regional High School stands. The highest level of this proglacial lake was at 600 feet elevation as indicated by the level of the glaciolacustrine terrace at the former Vail Gravel Bed in Falls Village. Proglacial Lake Great Falls (a.k.a. Lake Falls Village or Lake Sheffield) stretched twenty air miles from Great Falls in Amesville to the Stockbridge, MA border.

As in the case of other New England towns, the geology of Salisbury was determinant in how the early settlers lived. Trees were more than ample for building and heating. Plentiful tree bark and water permitted the tanning of hides, Despite the boulder-strewn soils, settlers managed to grow the necessary foods, Running water from Salisbury’s numerous streams provide the power for grist and saw mill. Following the discovery of iron ore in 1731, forges were put into production using limonite and goethite from local mines.

In more recent times gravel from kames and glaciolacustrine terraces was plentiful for the construction of roads and the making of concrete. With the advent of seven blast furnaces in town the tree population began to dwindle because of the use of wood for the production of charcoal fuel. By the 1890′s when larger, more productive dairy farms were in operation, more of the land was cleared for crops and grazing.

Today a portion of Salisbury’s heritage lies in the archaeological treasure constructed in the eighteenth and nineteenth centuries. Not the least of these treasures are the many stonewalls made by farmers clearing their fields annually of glacial deposits pushed to the surface by frost for over two hundred years.

In the present period where rocks are selling for handsome profits, landowners must be encouraged not to disturb these important remnants of a strong agricultural period. Where archaeologically important stone foundations are present, owners again have responsibilities. In regions where any of the local bedrock formations crop out, care should be taken concerning construction of roads, buildings and drilling of wells.
Sources and general location for the iron industry:
Limonite and Goethite—Ore Hill mines, Chatfield Mine, Porter Mine, Scoville Mine and others
between the Walloomsac schist and Stockbridge marble along the eastern slopes of the Western
Uplands
Lime—From Stockbridge marbles quarries primarily in Lakeville and Lime Rock.
Charcoal—From Mt. Riga, Mt. Easter in Lime Rock and Sharon, Sharon Central Highlands
and other areas.

From a Preliminary Geographic Topographic and geologic Review of the Town of Salisbury by
Edward Kirby

Further References:
Flint, Richard Foster (1930). The Glacial Geology of Connecticut (Bulletin #47). State Geological and Natural History Survey of Connecticut.
Kirby, Edward M. (2003). Exploring the Berkshire Hills. Geology Publications, Greenfield, MA.

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