I've fished every river mile of the Connecticut River from the Massachusetts border to the mouth at this point in my career, much of it extensively. Over the years I've taken note of how much of the bank structure, especially from Hartford to Haddam, consists of what would be considered non-native rock. Basically, non-native rock is any stone that originated elsewhere and was brought in. That can occur through natural alluvial or glacial processes but I'm specifically referring to quarries stone here, because there is a lot of it along the Connecticut. Being the artery of commerce, stone quarried nearby was often moved using the river. Some stone was also used to build landings and shore up banks. I'm more interested- at least in this context -in the history and origins of this stone than the impacts of it in an ecological sense. Of course putting rock along the edges of a stretch of river that flows otherwise through clay, sand, and gravel certainly does have consequences. I'm just a nerd here to talk about the history and geology of quarried stone in Central Connecticut because I think it's cool.
The vicinity of the Connecticut River, especially around halfway down it's journey through Connecticut, just so happens to be through some of the most exploited geology in the entire state. A map of Bedrock Mines and Quarries of Connecticut, compiled by Robert J. Altamura and published by the Connecticut Geological and Natural History Survey in 1987, shows just how densely clustered quarries and mines are in the area of South Glastonbury, Portland, Middletown, and Haddam. This is owed to a clash of different geologic formations. The Eastern Border Fault divides sedimentary sandstones to the west from metamorphic formations to the east along the Bronson Hill Anticlinorium. This metamorphic rock- including the Collins Hill Formation, Glastonbury Gneisses, and the Middletown Formation -is intruded by numerous pegmatites. Pegmatite is a coarsely-grained granite formed by intruding magma that cools slowly underground. It can be rich in feldspar, mica, quartz, and beryl, all of which have been historically very important in industry. Feldspar can be used as flux in ceramics and glass making. Connecticut was the chief producer of feldspar in the country around 1908. Quartz is also used in glass making as well as timepieces, and beryllium can be used in electronics and aerospace technologies. The heyday of these pegmatite quarries has long since passed, but they dot the wooded landscape not far from the Connecticut River. Some of this rock was moved via the Connecticut River, and some of it was left behind often as parts of the landings scattered along the banks. The discerning eye may even be able to parse which quarries this pegmatite came from simply by it's makeup. A minority of these pegmatites have lithium rich zones, denoted by the presence of minerals like cleavelandite, lepidolite, and elbaite. Bits of purple lepidolite and sugary white cleavelandite I found along the river bank one day, along with the proximity to the quarry itself, suggested I was likely walking on stone that had come from the Strickland Quarry or Schoonmaker Mine on Collins Hill. These piles of pegmatite are scattered about, mostly on the east banks with some on the west, from Glastonbury down to Haddam Neck.
Newer to the river basin is what we colloquially call traprock. Geologically this can be diabase or basalt, what I see most along the Connecticut River is more commonly basalt and is a more recent fill compared to the stone I've discussed already, some of it visibly fresh compared to the brownstone and granite pegmatite. The history of quarrying traprock also leans toward the present, comparatively, though some operations in this state do date back into the 1800's. Basalt is still a very heavily favored aggregate. Hard, fine grained, and fracturing into angular, sharp stones, it makes idea railroad beds, raid grades, asphalt, and as fill. As opposed to rounded stone, a hard and angular stone pile holds it's shape far longer. These characteristics are a result of the stone's chemical structure. Basalt is formed by the rapid cooling of iron and magnesium rich lava. That quick cooling means the crystals are small. The minerals that make it up- plagioclase, pyroxene, and olivine, are similarly hard. Unlike granite pegmatite, whose crystals are large and of widely varying hardness and often breaks along the edges of individual crystals, basalt has far less defined edges along which to cleave. The exception is columnar basalt which breaks along fissures formed while the magma cooled, but even within the individual columns any further fractures are going to be irregular. Basalt quarried in Connecticut has kept a lot of commerce and travel from going tits up throughout the years. The same properties make for a bank fill that won't wash out easily. These, in my opinion, are the ugliest man made rock piles along the river. I am not a fan of them and will dwell on them no longer. Instead, here is an image of basalt in it's natural habitat to end this little journey through the geologic history of rocks that do now but didn't always adorn the banks of Connecticut's namesake river.
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