Paterson's Geology - A Step Back in Time

What is Geology?

Geology is the science that studies and explains the physical structure of our Earth. It describes and characterizes the various rocks and minerals, and explains the processes that shaped land forms, above ground and under the ocean. Geology is both a practical science that is used by industry to locate mineral deposits, as well as a theoretical science that attempts to explain how the earth developed since it emerged from the original gas cloud that was the beginning of our solar system.

We can think of geology as the science of rocks. There are three different types of rocks: igneous rocks, metamorphic rocks, and sedimentary rocks.

Igneous rock is formed from lava, or magma, that has cooled into a solid.

Sedimentary rock is formed from sediments, such as the grains of sand, mud, dead vegetation, and even dead animals (like shellfish).

Metamorphic rock is formed when high temperature and pressure alter an existing rock.

View of the Great Falls and basaltic cliffs
A view of the Great Falls and basaltic cliffs.

V. Scott - NPS PHOTO


Geologically speaking, Paterson's past is a varied and exciting one. Lava flows, upheavals, even the break-up of the supercontinent Pangaea - these events are all part of this area's geologic pre-history. The Falls and other natural features in Paterson give us clues to parts of this story. As you walk over the Falls, through Upper Raceway Park, and around the Great Falls Historic District, you'll see some of these clues.

The Falls is in a river valley, but unlike other river valleys, such as that of the Colorado River, where the river eroded the Grand Canyon, the Paterson Great Falls was not eroded into its current form, instead the rocky structure that supports the Falls is virtually unchanged over the past 12,000 - 14,000 years that water has flowed over the rocky cliffs. Our Falls consists of basalt which is a fairly hard rock. In comparison, Grand Canyon consists largely of limestone and shale, with sandstone. Limestone and shale are much softer than basalt and so were far more subject to erosion.

When Paterson was established, our basalt and especially our sandstone were among the raw material that made Paterson an ideal place to establish an industrial city. Other raw materials were abundant wood, iron ore (nearby) and water. And with the Passaic River, we had water power. So while the SU.M. (Society for Establishing Useful Manufactures) was establishing a manufacturing city beginning with the spinning of cotton, the quarrying of stone was also important. The earliest local quarrying was done at Mount Morris - now just a rocky outcrop at the edge of Overlook Park. The “mountain” was quarried to oblivion for its supply of sandstone (brownstone). The Morris Canal made quarrying in Little Falls possible, and quarried stone could be transported via barge to cities from Paterson to New York. If you look at the oldest houses and churches in our area, brownstone is the most common stone used in construction.

As railroads were established, the tracks required a gravel roadbed and so the Watchung Ridge that touches Paterson was quarried for its harvest of basalt - traprock. Later on, traprock was used as aggregate in concrete, and by the 1920s it became the aggregate for asphalt roads (also known as blacktop). Traprock quarries followed the edge of the Watchung ridges, so were located along Valley Road in Clifton, in what is now Woodland Park, and in Little Falls where the newer sections of Montclair State University are located. By the way, Little Falls sandstone was used to build St. John’s Cathedral.

Garret Mountain and the Great Falls are part of a series of ridges known at the Watchung Mountains. These ridges were created by lava flows- a consequence of the breakup of Pangaea, the supercontinent that preceded the current arrangement of the earth’s land masses. In the case of the Paterson Falls, 225 million years ago, the super continent of Pangea began to show signs of an eventual split. The portion that now contains Paterson (and eventually became the North American plate) began to sink as the earth’s crust spread apart and thinned to form a deep rift valley. As the land masses moved away from each other, hot magma found its way to the surface through existing faults. A marker at Mary Ellen Kramer Park commemorates the 50 mile long lava flow that includes the Falls. The flows occurred approximately 190 million years ago.
The Palisades were formed similarly. Instead of being of basalt which is formed from lava (magma that comes to the surface) they are formed from diabase, a form of magma that intrudes close to the surface but not all the way to the surface. Diabase and basalt are similar in that they have small or tiny crystals of their composite minerals. Other igneous rocks like granite are formed from magma that is much deeper (usually forming as ocean crust). Granite and other similar rocks cool more slowly and thus the crystals are larger.

If you look at the exposed rock, you will also see signs of the glaciers that covered northern New Jersey, including the area where Paterson is located.

- Text by Volunteer in Park Terry

Last updated: November 18, 2022

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