Long Hill Township is in the Newark Basin of the Piedmont Physiologic Province.  Shales, that were deposited during the Triassic Period, underlie the town.  Volcanic activity occurred in the Newark Basin during the early Jurassic Period (181 million years ago).  As a result, fissures formed in the earth's surface and flows of basalt occurred on the surface.  Later faulting caused the flows to tilt.  which resulted in the formation of the Watchung Mountains.  A gentle uplifling of the earth in the region caused the streams to erode some of the rock layers. 

The "softer" rocks, those more susceptible to erosion, such as the Brunswick shale were gradually eroded, leaving the more resistant Watchung Mountains (Jurassic basalt) standing in relief.  In Long Hill Township the hard basaltic rocks of the Third Watchung ridge, known as Long Hill, define the topography and drainage patterns that currently exist.  Water falling on the north slope of the ridge drains into the Great Swamp, and on the southern slope moves towards the Passaic River. 

The most recent unit of geologic time, the Quaternary Period (the last 2.5 million years), included four glacial stages.  The most recent glacial stage, the Wisconsin Glacier reached its maximum extent in New Jersey about 18,000 years ago and began to recede 11,000 years ago.  Because of the great thickness (about 2,000 feet in New Jersey) and extent of the glaciers, much of the soil and large amounts of rock were dragged by or incorporated into the ice. 

When the climate began to warm, various portions of the glaciers began to melt.  The large quantity of sediments and rocks that the glaciers carried were then deposited.  The end of the glaciers southern movement in New Jersey is marked by the deposition of the terminal moraine.  The terminal moraine in Long Hill Township was deposited atop and alongside the Third Watchung Ridge.  This is important because of the superior capacity of the sand and gravel materials in the terminal moraine to permit rain or snow waters to infiltrate down to the underlying aquifers.  As a result of the Wisconsin glaciation, a lake known as "Glacial Lake Passaic" was formed in the Newark Basin between the Second Watchung Mountain and the Highlands.  Several remnant lakes occupied the lowland areas after the disappearance of Glacial Lake Passaic.  Swamps and marshes now occupy those remnant lake basins.  These include the Great Swamp, and the wetlands at the confluence of the Dead River and the Passaic River.  The sediments left on the slopes of Long Hill after Glacial Lake Passaic receded, now store ground water and release it slowly to the wetlands and the Passaic River.  These shallow, unconfined aquifers supply water to a significant number of private wells in Long Hill. 

This description is extracted from the "Township of Long Hill Well Head Protection Program Phase II: Identification of Well Head Protection Areas and Potential Pollutant Sources, June 2001".  The complete report has colored charts which accompany this text.  You may read the complete report by contacting the Secretary of the Environmental Commission.