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Green Pond Conglomerate (GPC) is a maroon colored quartzite with white quartz pebbles, a classic “puddingstone”. GPC derives from a NW-SW-trending sliver of Paleozoic sediments, the “Green Pond Outlier”, surrounded by older metamorphic and igneous rocks of Morris and Passaic Counties. Buildings, retaining walls, field fences, and monuments incorporate the durable and attractive stone, in a distinct geographic area of Morris County. Several instances of structures completely constructed or faced with GPC occur in and around Morristown, limited to affluent houses and one prominent church. In these cases, GPC stones were dressed and faced, a labor-intensive effort. Elsewhere in the county, GPC forms decorative accents to fences and walls, or in most cases, comprises a portion of the undressed rounded fieldstones in buildings and field fences.

No historic GPC quarries are noted, so the source of the building stone is from glacial sediments. The Pleistocene continental ice advances crossed and eroded the Green Pond outcrop from the north and Cand east of Morristown. Isolated Pre-Illinoisan deposits exist as far south as Somerset County, which may contain rare GPC cobbles. From Morristown and south, GPC as a building stone would likely have been imported. North of the terminal moraines, GPC is common and probably proportional to distance from the bedrock source. Ongoing research seeks to quantify the proportional frequency of GPC in human structures and in the glacial sediments.