Geology of the Sourlands
The Sourland Mountain is not your average, run-of-the mill mountain. Its highest elevation is 568 feet, which is fairly insignificant compared to the Rockies or even the Poconos. It is made of volcanic rock but there was never a volcano in this part of New Jersey. Everywhere you look near the ridge you see enormous, rounded and smooth boulders that look as if they were carried here by moving ice, but no glacier ever came within fifty miles of here. So how did the Sourlands come to be?
250 million years ago during the Triassic geological period, what is now New Jersey was in the middle of the “Pangea” supercontinent. As the Eurasian plate and African plate moved eastward and the North American plate moved westward, Pangea split up and the Atlantic Ocean was slowly created . Movements within the layers of earth under the surface caused what is now New Jersey to lie in a sort of huge basin, now referred to as the Newark Basin, running from New York in the northeast to Pennsylvania in the southwest. The basin was a huge freshwater lake, and over millions of years running water and other kinds of “weathering” carried sandy gravelly material off the higher ground into the basin below. This is what we know as the “Stockton Formation,” primarily made of sandstone and in places as thick as 1000 meters. Next, fine particles of silts, clays, and fine sands collected atop the sandstone and eventually hardened into black shale and argillite making what we call the “Lockatong Formation,” also about 1000 meters thick. Later came red and gray shales, along with more sandy particles, creating the “Passaic Formation.” All three of these are considered sedimentary layers.
Then during the Jurassic Age, between 195-135 million years ago, things got a lot livelier. Lava from the mantle below the Earth’s surface forced its way upwards and slid forcefully between the existing horizontal sedimentary layers, cooking the parts it touched, and cooling very slowly because it was not exposed to the cool air aboveground. Over millions of years as the tectonic plates continued to slide east and west the ground, no longer flat, was forced to fold up into what is now our Sourland Ridge, running about seventeen miles from northeast to southwest. All of this pressure caused large cracks, called faults, and smaller cracks, called fractures, which to this day form the primary source of groundwater storage for our wells in the Sourlands. Right up to today the softer layers of sedimentary rock have continued to erode, leaving the hard diabase and argillite layers to create our Mountain.