The Trenton Prong is a

physiographic Physical geography (also known as physiography) is one of the three main branches of geography. Physical geography is the branch of natural science which deals with the processes and patterns in the natural environment such as the atmosphere, h ...

subprovince of the Piedmont Uplands section of the Piedmont province of the

Appalachian Mountains The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...

. The prong consists of crystalline

metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causin ...

Location

The Trenton Prong stretches from near

Norristown Norristown may mean: * Norristown, Arkansas, an unincorporated community * Norristown, Georgia, an unincorporated community * Norristown, Indiana, an unincorporated community * Norristown, Pennsylvania Norristown is a municipality with home ...

Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...

, through northern

Philadelphia Philadelphia, often called Philly, is the largest city in the Commonwealth of Pennsylvania, the sixth-largest city in the U.S., the second-largest city in both the Northeast megalopolis and Mid-Atlantic regions after New York City. Sinc ...

and southern

Bucks County Bucks County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 646,538, making it the fourth-most populous county in Pennsylvania. Its county seat is Doylestown. The county is named after the English ...

, reaching its northern terminus in

West Windsor Township, New Jersey West Windsor is a Township (New Jersey), township in Mercer County, New Jersey, Mercer County, New Jersey, United States. Located within the Raritan River, Raritan Valley region, the township is an outer-ring suburb of New York City in the New Y ...

. The prong underlies much of the City of Trenton, and forms a series of

rapids Rapids are sections of a river where the river bed has a relatively steep gradient, causing an increase in water velocity and turbulence. Rapids are hydrological features between a ''run'' (a smoothly flowing part of a stream) and a ''cascade''. ...

known as the Falls of the

Delaware River The Delaware River is a major river in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. From the meeting of its branches in Hancock (village), New York, Hancock, New York, the river flows for along the borders of N ...

Geology

The Trenton Prong is part of the

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

basement which is discontinuously exposed in the north-central Appalachians. The rocks that make up the prong are mostly

Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and th ...

and

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

aged rocks, that includes the

Wissahickon Formation The Wissahickon Formation is a mapped bedrock unit in Pennsylvania, New Jersey, and Delaware. It is named for the Wissahickon gorge in Fairmount Park, Philadelphia. In Maryland formations, the term "Wissahickon" is no longer used. Rocks in this cl ...

. Other rocks present include

metabasalt Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flaky ...

gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is che ...

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures an ...

migmatite Migmatite is a composite rock found in medium and high-grade metamorphic environments, commonly within Precambrian cratonic blocks. It consists of two or more constituents often layered repetitively: one layer is an older metamorphic rock tha ...

and

granofels Granofels is a term referring to medium- to coarse-grained metamorphic rocks which have a ''granoblastic'' texture (having poorly formed, equi-granular crystal grains visible to the naked eye) and lack distinct foliation or lineation. The granofels ...

. The prong is heavily eroded, presenting as low, gently rolling hills.''Regional and Economic Geography of Pennsylvania: Physiography, Part 1'' Walter Sheldon Tower in ''The Bulletin of the Geographical Society of Philadelphia, Volume IV''; 1906, p 19

References

Appalachian Mountains Geology of Pennsylvania Geology of New Jersey {{PhiladelphiaPA-geo-stub