Then, gradually, imperceptibly, during the millions of years that followed this massive shifting of the earth, water eroded away the Newark sediments, exposing the jutting edges of the buried lava flows. These exposed basaltic edges, now much weathered by millions of years of rain, are what we call the First and Second Watchungs. Between them, in what we know as the Washington Valley, lays the crumbly red Brunswick shale. It is also rich in minerals, formed as water flowed over and through the cooling lava year upon millions of years. Amethyst, smoky quartz, prehnite, stilbite and chabazite are only a few of the 60-odd minerals found in the Watchungs.
Copper is also relatively abundant.
One of the finest collections of these minerals may be seen today at the American Museum of Natural History's Hall of Minerals and Gems. The geologic history of Warren does not end with the Late Triassic, l25 million years ago, or with the uplifting and tilting of the land during the Cenozoic. In relatively recent time, l50,000 to 200,000 years ago, great masses of ice advanced southward, scouring the land, blocking rivers, creating new lakes. Moving south at the rate of a foot each day, an impenetrable mountain of ice, perhaps 2000 feet thick, spread over New York City and environs. These glaciers advanced and retreated in ponderous cycles, finally departing the region 10-20,000 years ago.