Category Archives: Geology

Sailing Stones

Winter is coming to upstate New York so I decided to take us to the desert for this month’s column, specifically to the large, generally flat dry lake beds of Death Valley National Park in California.  For decades scientists have observed large rocks strewn about the playa surface and speculated about how they got there.  Often they are found with long, sometimes curved tracks suggesting movement across the desert surface.

A solitary “sailing stone” on the Raceway Playa in  Death Valley.                        (from Google Wikipedia)

A solitary “sailing stone” on the Raceway Playa in Death Valley. (from Google Wikipedia)

In the past, many theories were proposed to explain how rocks, some as heavy as 700 pounds, could slide or sail across the dry lake bed creating a furrow or trail in their wake.  Hurricane force winds and muddy playa surfaces were suggested.  Slick algal mats present during rare wet periods and thick ice accumulations were also proposed, but experiments and models developed with these ideas could not duplicate the phenomena.  Furthermore, it did not seem reasonable that roving herds of pronghorn antelope had entertained themselves by pushing stones around while no one was watching.  Besides there were no hoof prints!

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Balmat-Edwards Zinc District – Geology

Mineral collectors know about the fine magnetite, sphalerite, hexagonite, chrome tremolite, lazulite, etc. that have come from the various mines in the Balmat-Edwards Zinc District of upstate New York. Mineralogists have studied the district for decades discovering new minerals like turneaureite and donpeacorite.  But seldom are we offered such a wonderful opportunity to learn the geology of the district as afforded those attending the New York State Geological Symposium  in Alexander Bay in October.

The opening address was delivered by William deLorraine, Chief Geologist for St Lawrence Zinc Co. in Gouverneur, NY.   Bill is also the President of the St. Lawrence County Gem and Mineral Club.  Continue reading

Rochester Shale – Silurian Fossils

An article I wrote for the April 2014 WCGMC News

The Rochester shale comprises the upper 85’-90’ of the Middle Silurian Clinton Group in upstate New York and southern Ontario.  The upper two-thirds of the unit contain numerous grey limestone beds, which can be sufficiently resistant to form outcrops, but which are poor in fossil content.  The lower 20’ of the Rochester shale is notoriously susceptible to erosion such that outcrop exposure is rare.  Unfortunately, it is this rapidly weathering unit at the base that contains the abundant fossil assemblage (specifically trilobites) for which the formation is famous.  The best visible exposure of the full Rochester shale section is in the gorge walls of High Falls on the Genesee River.  However, this section is agonizingly unapproachable for fossil collection, particularly so the lower 10-20’ of section best known for fossil diversity and abundance.

Over 200 invertebrate fossil species have been identified from the Rochester shale including corals, brachiopods, bivalves, gastropods, cephalopods and crinoids.  But, it is the spectacularly preserved trilobites that have attracted collectors to the Rochester shale since James Hall first detailed their occurrence in the 1840’s.  The diverse fauna combined with the fine grained shale beds and thin limestone units indicate that the Rochester shale was deposited in warm, well oxygenated marine waters of intermediate depth.   But where does one find outcrop to search for fossils?

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Geologic Time

Article I wrote for the March, 2014 WCGMC News

If Time is Relative, Geologic Time is Exponentially Relative

The geologic time scale is a difficult concept for humans to appreciate.  We live less than 100 years, the Vikings came to America 1000 years ago, our current calendar just passed the 2000 year mark, and Stonehenge dates almost 5000 years old.  That, we say, was a long time ago.   But these are mere seconds on a geologic clock. Even the final Ice Age advance that generated upstate New York’s topography and fertile soil ended a mere 12,500 years ago.

Now think about this.  Dinosaurs roamed and dominated much of the planet for the entire Mesozoic Era.  For over 160 million years (MY) they lived, and died until going extinct about 65 million years ago.  By comparison, humans have been inhabitants for just under one million years.  And all but the last 6000 years or so of that is referred to as the Stone Age, the period before metal was worked and likely before crops were cultivated.

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Wolf Creek Dam, Kentucky

Geology in Action, Wolf Creek Dam, Lake Cumberland, Kentucky

The construction of Wolf Creek Dam in central Kentucky began in 1941, but work was interrupted by WW2 and the dam was not completed until 1951.  Potential problems with the integrity of the underlying Ordovician Leipers limestone were appreciated during construction and extensive cement was placed in a number of cave features that were known to exist before the earthen dam was built above.  However, that early work proved to be insufficient in preventing seepage from Lake Cumberland through the underlying karst.

dam11947 photograph highlighting cavernous regions in the dam’s base that were filled with cement.

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