Geology of the Ellwanger-Barry Neighborhood

map of glacial deposits
Figure 1.  A sketch map of the glacial deposits in the Rochester area.  The Ellwanger-Barry neighborhood is outlined in red in the southeast quadrant of the city.  Map by H.L. Fairchild in Geologic Story of the Genesee (1928).
The Ellwanger-Barry neighborhood is located between I-490 to the north and the Pinnacle Range, which forms the southern boundary of the city between the junction of I-590 and I-490.  I-490 was built on top of the old commuter-rail line that led out to Pittsford.  Those tracks had been laid on the old path of the Erie Canal, which came in from Pittsford to the east and crossed the Genesee River on what is now Broad Street in downtown Rochester.  The canal was moved to its present location (cutting through Genesee Valley Park) early in the 20th century.

The Erie Canal was built in its original location because there is a natural east-west lowland between the Niagara Escarpment to the north and the Onondaga Escarpment to the souther.  Downtown Rochester is built on the Niagara Escarpment and Buffalo and Syracuse are built on the Onondaga Escarpment.  The rocks of the Niagara escarpment would not be a particularly visible in this region except that in the last ~10,000 years the Genesee River has cut down into the local bedrock to form the Rochester Gorge.  The top of the escarpment is made up of the dolomite rock of the Lockport Group; these rocks are visible in the bed of the river between the Court Street Dam and the High Falls.  (For more information about Rochester geology, look here .)

Court St. Dam rocks
Figure 2.  Lockport Group rocks exposed in the Genesee River bed north of the Court Street dam. Photograph from T.G. Payne's The Genesee Country (1938).
The dolomites (similar to limestone, but rich in magnesium) of the Lockport Group are buried deep beneath the Ellwanger-Barry neighborhood under many meters of glacial moraine.  The dolomites were formed in a shallow tropical sea 420 million years ago.  At that time the proto-North American continent was located in the subtropics of the southern hemisphere (~25°S).  The Rochester area may have looked something like the modern Bahamas, but the carbonate platform was located in the continental interior.  The glacial moraine (unstratified sediment derived directly from the ice sheet) was deposited during the last advance and retreat of continental ice sheets between 120,000 and 10,000 years ago.
Brighton boulders
Figure 3.  A woodlot strewn with dolomite erratics.  This location is actually in Brighton, but the Ellwanger- Barry area likely looked like this before it was cleared for timber in the 19th century.  Photo from Fairchild (1928).
There is no bedrock outcrop in the Ellwanger-Barry neighborhood, but excavations in the area often unearth large boulders of Lockport dolomite.  These were dislodged from the bedrock by the ice sheets of the Pleistocene Epoch (last 1.7 million years of Earth history).  They are sometimes deposited by the ice many miles from their point of origin.  For this reason they are called 'glacial erratics'.  But most erratics are actually deposited a few hundred yards after they are picked up by the ice, as is the case for the Lockport blocks derived from the Niagara Escarpment and found in the Ellwanger- Barry neighborhood.

BUILDING THE LANDFORM: Some early ideas

1843
 The first description of the Pinnacle Range in the geological literature was made by James Hall. He made a sketch of the cutting created by construction on Monroe Avenue.
1890
 Charles Dryer referred to the range as a "gigantic kame" and noted that "the lower half is composed of coarse gravel and the upper half of sand. A kame is composed of stratified sediment deposited by glacial meltwater into either a periglacial lake ("kame delta") or into a supraglacial lake.
1892
 Warren Upham referred to the range as an esker. This was completely incorrect. Eskers are composed of stratified sediments deposited in sub-glacial streams.
1923
 Herman LeRoy Fairchild, professor of geology at the University of Rochester, accurately described the formation of the range in Proceedings of the Rochester Academy of Science, 6:141-194.

pinnacle
Figure 4.  Pinnacle Hill in 1895 looking west from Cobbs Hill.  The Ellwanger-Barry neighborhood can be seen in the middle distance on the right side of the photo.  Cobbs Hill Reservoir was over a decade in the future.  Photo by H.L. Fairchild.
Only at Pinnacle Hill is the range a single ridge. Elsewhere it is broken up by kettles. Kettles are depressions that form when large blocks of glacial ice are left buried in proglacial sediment after the main body of the ice sheet melts back. After the ice melts, a depression remains on the landscape. "Kettle and kame terrain" is indicative of an episode of rapid ice-sheet recession.  In addition to the natural depressions created by the kettles, there are numerous depressions that are  the remains of old gravel quarries.  Quarrying created the valley behind Lamberton Conservatory in Highland Park.
stratified sands
Figure 5.  When Goodman Street was built over the Pinnacle Range the ridge was excavated to lower the grade of the road.  These stratified beds of glacial lake sands were exposed in Highland Park in 1894.  Photo by H.L. Fairchild.
The north slopes of the Pinnacle Range were originally irregular, studded with spurs and ravines, partly erosional and partly caused by ice-contact. The south slopes were less steep with the lower portions fairly uniform; they were formed by outwash. The sediments that make up the bulk of these hills were deposited into a periglacial lake called Lake Dana ~11,000 years ago. Hence their bases are composed of more or less horizontal beds of sand and gravel.

kame delta 1

Figure A. The angle of the deltaic bedding and the thickness of the ground moraine are exaggerated in this figure. The bedrock below the moraine is dolomite of the Lockport Group, which is exposed in the Rochester Gorge and on I-490 and Rt. 590 near the "Can of Worms".


 kame delta 2

Figure B. After a ridge of stratified sediments, the ice sheet melted back a short distance, leaving behind erratics and a mantle of moraine (not shown) on the north side of the kame delta.
kame delta 3

Figure C. A brief glacial re-advance plowed unstratified material up onto the kame delta and disrupted the bedding of the kame delta (not shown).


kame delta 4

Figure D. During and after the lowering of the pro-glacial lake level from Glacial Lake Dana (El. 700’) to Glacial Lake Dawson levels (El. 460’), erosion removed some of the lake sediments deposited in Dana and re-deposited them in the Irondequoit Valley and elsewhere.

The Pinnacle Range As a Natural Resource

A.E. Dumble took a walk one spring morning in 1886 and wrote about it in two articles for the Democrat & Chronicle . These were reprinted in The Pinnacle 25 years later and again in The Pinnacle Hill Trail Project in 1976.

Dumble rode to end of the street-car line, disembarked and crossed the canal. This former street-car stop is presently the site of the Monroe Avenue overpass on I-490. He then cut through Crosman’s nurseries (now the Laburnam Crescent vicinity) on the way to "the bare grassy hill immediately to the east of the Pinnacle cemetery".  It was an Irish Catholic cemetery located at the junction of Clinton Avenue and Field Street, which  at the time was called "Paddy Lane".

The southern edge of the city is described as being "at a distance of a long rifle shot"and the intervening fields are full of "great boulders of conglomerate limestone and granite".

The hill had already been excavated for gravel, which had left "a great chasm ...100 feet wide and from 50 to 100 feet high" and the pits were active on the day of his visit. In fact, he spotted a coffin hanging half-way out of the wall of the pit.  This pit can be seen today on the south side of the hill .

Between the time of Nathaniel Rochester's original 1811 survey of the 100 Acre Tract for residential lots and Dumble’s walk —75 years— the Pinnacle Hill vicinity had been:
  • cleared of timber —only scattered ancient oaks remained
  • perhaps grazed —no fences are described, but the land is presumably kept open somehow
  • quarried for gravel —Dumble does not describe a use for the gravel, but it was frequently used as fill for road construction and for making concrete.
  • in use as a Catholic cemetery, including the grave of Civil War hero Patrick O'Rorke.   Most of these graves, including Colonel O'Rorke's, were moved to Holy Sepulchre Cemetery in the 1930s, but some remain, mistakenly left behind.


What Could Be Done to Preserve Pinnacle Hill?

In 1997 the Historic Landscape Initiative by the National Parks Service is put forward to preserve "those special places that reveal aspects of our country’s origins and development through their form and features and the ways they were used. They include both designed and vernacular landscapes."
The Park Service guidelines suggest "identifying, retaining and preserving the existing spatial organization and land patterns as they have evolved over time. Prior to beginning project work, [one should] document all features which define those relationships. This includes the size, configuration, proportion and relationship of component landscapes...." This includes topography, vegetation, circulation and accessibility and environmental considerations. There are three sets of guidelines for preservation, rehabilitation and restoration.
The definition of a Historic Vernacular Landscape: "A landscape that evolved through use by the people whose activities or occupancy shaped that landscape. Through social or cultural attitudes of an individual, family or a community, the landscape reflects the physical, biological, and cultural character of those everyday lives. Function plays a significant role in vernacular landscapes. They can be a single property such as a farm or a collection of properties such as a district of historic farms along a river valley. Examples include rural village, industrial complexes, and agricultural landscapes."

  • Develop a strategy and seek assistance from academics and landscape professionals.

  • Do historical research.

  • Prepare period plans. These document the appearance of the land at a particular period

  • Inventory and document existing conditions. Prepare existing condition plans. These should include plans, sections, photographs, aerial photographs, narratives, video. Record features that contribute to the landscape’s historic character.

  • Evaluate the integrity and significance of the landscape. The seven qualities of integrity are location, setting, feeling, association, design, workmanship and materials. Significance is determined through the National Register criteria.

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