Portland, Middlesex Co., Connecticut, USA
|Latitude & Longitude (WGS84):||41° 34' 22'' North , 72° 38' 28'' West|
|Latitude & Longitude (decimal):||41.57278,-72.64111|
|Köppen climate type:||Dfa : Hot-summer humid continental climate|
Known as "Quarrytown" primarily for the large "brownstone" quarries (aeolian arkosic sandstone of the Portland Formation) near the Connecticut River in the western part town, Portland is also host to the most famous pegmatite quarry in the area - the Strickland Quarry. Coordinates are for the downtown intersection of State Routes 17A and 66 in the west, which is far removed from the pegmatite quarries farther east.
European settlers arrived in the 1690s, attracted to the blocks of brownstone along the riverbank. Originally Portland was part of Middletown and was known as East Middletown. In 1767 it became the separate town of Chatham. In 1841, when it separated from the eastern part of Chatham, it changed its name first to Conway then to Portland (because of the fame of quarries in that English town) (The remainder of Chatham changed its name to East Hampton in 1915.)
The bedrock geology is split between continental sedimentary rocks in the west, part of the Mesozoic Hartford Basin of the Newark Supergroup and mostly metaplutonic, metavolcanic and metasedimentary metamorphic rocks of the Ordovician Bronson Hill terrane in the east. These terranes are separated by the Eastern Border Fault of the Hartford Basin. Much of the Bronson Hill terrane rocks in town are mixed schists, calc-silicate rocks, and minor quartzites of the Collins Hill Formation, and its metavolcanic member, which are present just east of the Eastern Border Fault. Farther east the bedrock is mostly metaplutonic Glastonbury Gneiss, which crops out as far south as Great Hill Pond. A thin sliver of Devonian Maromas Granite Gneiss is also present.
Portland lies within the Middletown Pegmatite District, and a swarm of Permian pegmatite dikes lies just east of the Eastern Border Fault, mostly within the Collins Hill Formation, but some further east in the Glastonbury Gneiss. These were heavily quarried from the north at the Glastonbury town line and just east of State Route 17 (particularly the long-lived Hale Quarry) southward onto Collins Hill, which hosted the famous Strickland Quarry and Cramer Mine, where most of Portland's diverse mineralogy originates. Most pegmatite specimens just labeled "Portland" are likely from there, although the small Walden Gem Mine and Case Quarries produced many specimens also. Sharply formed and deeply colored aquamarines hail from the small Pelton's Quarry. Unquarried pegmatites can still be easily seen along State Route 66 in the Riverdale section just north of the Connecticut River in the area known as "The Ledges".
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120 valid minerals.
Rock Types Recorded
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This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
174.1 - 201.3 Ma
Age: Early Jurassic (174.1 - 201.3 Ma)
Stratigraphic Name: Portland Arkose
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. 
201.3 - 252.17 Ma
|Mesozoic volcanic and intrusive rocks|
Age: Triassic (201.3 - 252.17 Ma)
Comments: Connecticut Valley Basin
Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. 
Localities in this Region
- Middlesex Co.
- Andrews Quarry (old Hale Quarry; Grandfather Andrews Quarry)
- Appletree Lane
- Bordonaro Quarry
- Case Quarries
- Collins Hill
- Middlesex Co.