John Bryan

John Bryan (HM1GN0)

Location: Yellow Springs, OH 45387 Greene County
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Country: United States of America
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N 39° 47.653', W 83° 50.468'

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— Part of the Clifton Gorge/ Glen Helen Complex —

The history of the earth is written in rocks.
In Ohio, nearly 500 million years of time are
recorded in our bedrocks, reflecting the coming
of the inland seas, the upheaval of the mountain ranges
and the birth and death of great swamps. By
reading these rocks, geologists can piece
together our ancient history. No matter where
you walk, geology in some form awaits discovery.
In this park, though, it influence and impact is

Ohio bedrock is all sedimentary. It was laid
down upon the floors of the ancient oceans which
periodically inundated the state. Conditions changed over the eons in these waters, dictating the different types of sediments that we now see as bedrock. Compaction over subsequent millions of years, compressed the materials into rock.

Ohio general bedrock types include sandstone, shale and limestone. The first two are formed from sediments washing into the sea from nearby land masses. Sandstones and comglomerates represent periods when coarse-grained and larger materials were introduced from relatively swift flowing rivers. Shales are former from finer sediments such as muds. Limestone usually represents an area where the sea was deeper and clearer. Lime precipitates out of the water, accumulating as a mud with many shell fragments on the sea floor.

As seas receded and the resultant lowlands grew lush with swamp vegetation, the coal measures of eastern Ohio were formed. As seas alternately flooded and withdrew from the region, salt waters killed the vegetation, and brought in the sand and mud seen today as layers of coal interspersed with sandstone and shale.

Ohio sedimentary rocks form layers with the oldest strata at the bottom. These layers dip slightly to the southeast and northwest in the corners of the state while they are fairly level from Cincinnati north to Toledo. This dome or arch is a feature of the bedrock itself while surface erosion has cut evenly across the state. Therefore, different layers are exposed across Ohio with the oldest at the center of the arch and younger layers in the southeast and northwest.

Clifton Gorge of the Little Miami River here at John Bryan stands in sharp contrast to the relatively flat landscape of most of western Ohio. Rock and soil debris, spread over three fourths of the state during the Pleistocene Ice Age, buried most old bedrock valleys. Here, however, the story is obviously different.

The continental ice sheet blocked the preglacial routes of many streams including that of the Little Miami. Glacial meltwaters then rapidly cut this new spectacular 70 foot deep gorge for the river through middle Silurian dolomite.

During the period 420 million years ago when this bedrock was formed, all but the southern extremeties of the state were covered by water which teemed with life. The shells and lime precipitants that accumulated hardened into limestone and then changed into the magnesium rich dolomite seem in the park today.

A spring walk through the gorge is a very pleasant experience. A wild diversity of wildflowers flourish in the rich soils while warblers sing from the budding trees. Nowhere is the show of bluebells and hepatica quite so pretty as beneath these towering cliffs and on the banks of the pristine, officially designated Wild and Scenic River.
HM NumberHM1GN0
Placed ByOhio Department of Natural Resources
Marker ConditionNo reports yet
Date Added Wednesday, October 1st, 2014 at 2:20am PDT -07:00
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Locationbig map
UTM (WGS84 Datum)17S E 256737 N 4408779
Decimal Degrees39.79421667, -83.84113333
Degrees and Decimal MinutesN 39° 47.653', W 83° 50.468'
Degrees, Minutes and Seconds39° 47' 39.1800" N, 83° 50' 28.0800" W
Driving DirectionsGoogle Maps
Area Code(s)937
Which side of the road?Marker is on the right when traveling North
Closest Postal AddressAt or near Unnamed Road, Yellow Springs OH 45387, US
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