NY I-84 Rocky Conclusions (PN-EC) EarthCache
NY I-84 Rocky Conclusions (PN-EC)
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This is an earthcache, which is a type of virtual. That means there is no container. Read the description and complete the logging requirements listed at the top of the description. For more on earthcaching visit www.earthcache.org.
NOTE - since this ECs creation, the foliage has covered much of the formation. Please do the best you can!
This earthcache is a "Park and Grab" just off Interstate 84 Exit 14. It is roadside, available regardless of your direction of travel. Shoulder is wide, please use it. DO NOT pull over on the Interstate!
Logging Requirements:
You will see TWO types of exposures described below at the GZ/Waypoint #2. Your overall goal is to be able to identify the distinctive differences of this "confluence" of geologics.
1. At GZ, look for Gneiss. Its is a slightly "textured" rock at GZ and "pushed" through the surrounding rock.
A. Where is the Gneiss Hudson Highlands uplift in relationship to GZ?
B. measure the WIDTH of one of the quartz veins at GZ. C. Estimate the width & height of the uplift. D. Would you describe the Gneiss as "layered" or "swirled" (or both)?
2. Between GZ and Waypoint #2 (N 41 32.107 W 073 48.683) -
A. Find a SLICKENSIDE and describe how it differs from the base rock
A. DESCRIBE - Find the "other" rock present at GZ (Dolostone -- Wappinger Group) and describe it. (You may find it helpful to test its hardness, its texture, and whether it has visible crystals, is layered, coloration: gray, brown, red, purple etc.) This isn't a trick question - if you have ever experienced Dolomite, it is the same here! If you live in the region, your gravel driveway probably is dolostone so it probably looks the same!
B. LOCATE - Where did you see the best exposure of dolostone? (beyond GZ, near GZ, near Waypoint #2, slightly past WP#2)
NOTE: There is the potential that Sedimentary, metamorphic, and igneous rocks are all present at GZ. To read brief descriptions of these three rock types/the rock cycle visit: Learner.org "Rock Cycle"
Interstate 84 between the Connecticut state line and Port Jervis crosses the structural grain of the northern end of the Hudson Highlands, southern end of the Taconic Klippe, and the Ordovician lowlands of the Wallkill Valley. It gives us a great "cross-section" of the geology of this part of the state/region in a relatively short distance (VanDiver 121).
You are on the border between the highly deformed gneisses of the Hudson Highlands (oldest rocks in NY) and the dolostones of the Ordovician Wappinger group. In reality, we are mostly in the Ordovician Wappinger group at this point, but in this transitional zone, there are several uplifts or blocks of basaltic Highlands gneiss...you might see them here!
HUDSON HIGHLANDS is the oldest rock in the state. the gneiss in this formation was formed in the core of the Ancestral Adirondacks during the Grenville mountain building event. This mountain range (no longer existant) formed a rim coastline well inshore, extending from Labrador (Canada) to Mexico (121).
TACONIC KLIPPE (Austin Glen) are a remnant of uplift geology from the Taconic Mountains (Himalayan sized mountains of antiquity). They are mostly metamorphic slates and schists that either slide down these huge mountains, or are pushed up from below as a "piece of misplaced crust rock." (11).
How do you know what you're looking at? Here are some things you MIGHT see here (all are present in the region but not all visible here)
GNEISS (Hudson Highlands): If you're looking at the gneisses, an indicator is intrusions ("veins") of quartz -- a white translucent or milky white mineral) threaded through the rock. The gneisses will also often appear "swirled" with a layer-like look (gneiss is actually metamorphic, but it looks like a sedimentary rock).
GRAYWACKE or SHALE (Austin Glen/Taconic Klippe): Also in this zone (and westward to Beacon, are the beginnings of graywacke and shale of the Austin Glen formation (metamorphic rocks). Shales that have been metamorphed in this area often have "slickensides" and show "fissale" layers when in exposures.
- SLICKENSIDE: shiny polished shale surfaces, like they've been rubbed/polished by a sanding machine. In reality they have, thousands of feet underground as the uplifts have rubbed and pressed them against other hard rocks while still underground.
- FISSILE: Shale is made from hardened and compressed clay. Clay molecules are flat, so when they compress they compress in "paper thin" layers, and peel back like an onion skin!
DOLOSTONE (Wappinger group): When in mineral form, Dolomite is pretty -- yellowish to clear crystals. Here in this area though its light gray, somewhat course, composed of non-distinct grains of the mineral dolomite. It is a sedimentary rock. "It is thought to form by the post depositional alteration of lime mud and limestone by magnesium-rich groundwater." "Both dolostone and limestone are crushed and cut for use as construction materials and used for their ability to neutralize acids." (geology.com).
Resources:
VanDiver, Bradford B. Roadside Geology of New York. Missoula: Mountain Pub., 1985. Print.
Geology.com http://geology.com/rocks/dolomite.shtml
FTF: big dawgs
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