What Kind of Rock Lies Beneath the Northwoods?

As the young scholar wanders Skidmore’s northern woodlands, he or she may come across any number of rock outcrops. In all likelihood, those outcrops, when unweathered by Earth’s climate, will have a medium to dark–gray color and a fairly coarse crystalline structure. Such rock, known as dolostone (CaMg(CO3)2), spans Skidmore’s Northwoods land. Very sporadic outcrops of sandstone and limestone (CaCO3), a close relative to dolostone, also appear on the property. Moreover, erratic boulders, vestiges of the last ice age, are also sparsely present, and a sedimentary rock known as chert appears intermittently; nonetheless, dolostone’s frequency in Northwoods is unmatched.

The question thus arises: how did all of this dolostone end up in our backyard? During the Ordovician Period of Earth’s history, from approximately 488 million years ago (Ma) to 444 Ma, Saratoga Springs (and North America) was much nearer to the equator than it is today; by virtue of plate tectonics, the future New York State occupied a tropical location in a world climatically warmer than today’s Earth. Sea levels were higher, and shallow seas covered Saratoga Springs. Consequently, tropical organisms with CaCO3 shells abounded and settled on our seafloors, ultimately lithifying as limestones. Later, briny fluids related to such a tropical environment probably flowed through those limestones, gradually replacing much of the limestone’s calcium with magnesium—forming dolostone. In later (millions of) years, other materials covered the dolostone; however, Earth’s climate, by the present, has largely eroded any layer(s) that used to overlay the Northwoods. And, hence, we have dolostone.

So, the next time you find yourself tripping over inconspicuous outcrops in Northwoods, keep in mind that you’ve fallen upon the closet thing to a tropical beach that Skidmore may ever enjoy (I can already hear the Environmental Studies Department’s exclamations of rising sea levels… What about the polar bears?). In all seriousness, you will be walking across history—not human history; but, perhaps, history bigger than humans, history representative of a world long before us.

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