Published in Epitaph (newsletter of the Friends of Mt. Hope Cemetery) Winter 2004


EVERYTHING YOU WANTED TO KNOW ABOUT THE GEOLOGY OF MOUNT HOPE CEMETERY

by William Chaisson

(Editor's Note: Bill Chaisson is a professor of geology at the University of Rochester. In this article, he takes us through mythological ideas about the formation of the earthís surface to the major scientific discoveries that ascertained the existence of massive global  glaciers that created the interesting landscape of Mount Hope Cemetery and the surrounding area. These glaciers present a fascinating story, and a tale that is true.)

HISTORICAL BACKGROUND
PLEISTOCENE GEOLOGY
PINNACLE RANGE GEOLOGY
GEOLOGY OF MT. HOPE CEMETERY
     Till and Moraine
     Gravel Pits and Natural Depressions
     Kame Sediments
     Kettles
     Glacial Erratics
     Local Bedrock
SUMMARY
ADDITIONAL READING

The jumble of hills and glens in Mount Hope Cemetery is a largely natural rather than an anthropogenic (created by humans) landscape. Indeed, it was the steep-sidedness and irregularity of the area that probably led to its use as a burial ground; it was picturesque, and, after some initial gravel quarrying, it apparently wasn't good for anything else. The former St. Patrick's Cemetery on Pinnacle Hill was apparently built on its site for similar reasons. However, consolidations of the neighborhood Catholic cemeteries to Holy Sepulchre in the late 19th century permitted the resumption of quarrying at Pinnacle Hill. As a result, much of the natural shape of Pinnacle Hill has been put into horse-drawn carts and carried away. In contrast, the continuous use of Mount Hope as a cemetery since 1838 has also preserved an incomparable glacial landscape. 

Mount Hope Cemetery was built on the eastern quarter of a row of hills called the Pinnacle Range. In a city where topographic drama is elsewhere provided by holes in the ground like the Genesee Gorge, the Irondequoit Valley, and the gullies of Durand-Eastman Park, the Pinnacle Range represents the only significant positive relief. The Pinnacle, the tallest hill in the range, lies between South Clinton and Monroe avenues and rises 263 feet above the surrounding plain. The knolls of the Irondequoit Valley and Durand-Eastman Park are incidentally left standing higher as a result of running water incising and eroding the sediments around them, while the Pinnacle Range hills were actively built during the latter states of the last glacial retreat.

HISTORICAL BACKGROUND

The Pinnacle Range entered the geological literature in 1843 when James Hall, New York State geologist, published the first description of the ridge. He included a sketch of the sediments revealed by the excavations done to lower the grade of Monroe Avenue on its way out of the city and into Brighton. At this early date, Hall would not have guessed the true agent for the construction of hills. From the 17th to the latter half of the 19th century, the scientific community generally accepted the hypothesis that Noah's Flood was responsible for the form and distribution of much of the unconsolidated material found on the Earthís surface. Because this debris was thought to have been transported and deposited by water, it was called "drift".

During the Renaissance (15th and 16th centuries), scientific explanations for natural phenomena began to replace mythological stories. The hypotheses to explain the form and operation of Nature became increasingly ambitious in the 17th century. Thomas Burnet (1635-1715), royal chaplain to King William III of England, published his Telluris Theoria Sacra, or The Sacred Theory of the Earth in 1861. One of Burnet's primary assumptions was that he was living in a "fallen world". Before the commission of the "original sin", the world had been a perfectly orderly place. Burnet sought to explain the erosion, decay, and disorder that he saw on the landscape, and he attributed much to the violence and scale of the Noahic flood. Through the 18th century, as more field work led to more extensive mapping of drift deposits, this "diluvial theory" was gradually refined. It would have been Hall's assumption, as he sat in the middle of a construction site on Monroe Avenue in 1843, that he was sketching sediments deposited in a global flood. 

In the 1830s, Swiss paleontologist and zoologist Louis Agassiz (1807-1873) began taking walks in the Alps with mountain guides. These were men with little education, but years of experience traveling in the mountains. They showed Agassiz the deposits left on valley floors after glaciers had melted back decades before. The professor was struck by how similar these alpine deposits were to piles of drift that he had observed much further north in southern Germany, some distance from the mountains. Using the premise that similar results have similar causes, Agassiz hypothesized that the alpine glaciers had been much more extensive in the distant past. Agassiz threw himself into the scientific literature on this new topic and found that drift deposits similar to the alpine glacial sediments could be found over much of Europe and North America. In 1840, he published "Etude sur les Glaciers", wherein he proposed the existence of a global ice age in the geologic past. Agassiz was an enthusiastic and tireless lecturer, and he immediately began a campaign throughout Europe to replace the diluvial theory with the glacial explanation for drift deposits. 

In 1846, three years after Hall's initial examination of the Pinnacle Range, Agassiz moved to the United States and published "Systema Glaciare" (1847) on the strength of extensive field work throughout Europe. After 1848, he accepted a professorship at Harvard University, did more field work in North America, and actively introduced the glacial theory to the New World geologic community. Largely because of more rigid religious beliefs from those of their European colleagues, the North American geologists took longer to be won over. As late as 1891, prominent Canadian geologist Sir J. William Dawson (1820-1899) was still actively defending the diluvial theory, which had long since been abandoned by the European establishment. 

But through the second half of the 19th century, the glacial theory gradually gained more American adherents. In 1890, geologist Charles Dryer noted that the lower half of the Pinnacle Range was composed of coarse gravels, while the upper half consisted of fine sands. He called the entire ridge a gigantic kame, a term of Scottish origin that refers to layered or stratified sediments that are derived from a glacier, but deposited into a body of water. Two years later, another geologist Warren Upham, impressed by the linear form of the chain of hills, claimed it was a very large esker. the sediment accumulation in the channel of a sub-glacial river. In 1895, Herman LeRoy Fairchild (1850-1943), a geology professor at the University of Rochester, showed that Dryer was closer to the truth than Upham. 

PLEISTOCENE GEOLOGY

H. L. Fairchild's major achievement as a research geologist was his mapping of a series of glacial lakes that ponded in front of the retreating continental icesheet between 18,000 and 9,000 years before the present time (B.P.) at the close of the last glacial cycle. The topography of western New York State rises steadily from the Lake Ontario basin to the Pennsylvania border, which is why the Genesee River flows north. As the southern edge of the icesheet retreated northward across the state, the meltwater collected between the towering ice mass to the north and higher ground to the south in a series of enormous "proglacial" lakes. Fairchild gave each lake a name as it dropped to a lower level and drained either west through the Mississippi drainage or east through the Mohawk or St. Lawrence Valley. 

By approximately 10,000 years B.P. [before present], the southern edge of the icesheet had melted back to the latitude of Rochester. The center of this great ice mass was over the northern part of Hudson Bay, Canada. For tens of thousands of years, it had been so cold there that the snow that fell each winter was not entirely melted away during the succeeding summer, causing a net accumulation of snow. Over millennia, this accumulation became so thick that the perennial snow was condensed to ice. Eventually the ice was condensed to the point where it became a plastic solid, flowing away from the thicker center toward the thinner edges. 

Over approximately 100,000 years (120,000 to 20,000 B.P.), the latest incarnation of this continental icesheet grew from its center near northern Hudson Bay to cover a third of North America. This most recent glacial advance is called the Wisconsinan, because significant glacial deposits can be found in that state. Traditionally, three previous glacial advances are described from the North American continental record (the Nebraskan, the Illinoian, and the Kansan) with corresponding coeval deposits found in Europe. However, over the past 25 years, analyses of stable isotopes in deep-sea carbonate records have revealed that the latest ice age in Earth history began approximately 3.2 million years ago and that the amplitude of glacial-interglacial cycles has been gradually increasing since then. 

The plastic consistency of the ice, its enormous weight, and its dynamic nature caused it to tear apart the landscape as it moved over it. Pieces of rock of all sizes--from clay particles to blocks as big as buildings--were absorbed into the ice mass and carried along, sometimes for hundreds of miles. At the edges of the icesheet, this load of sediment was disgorged. Sediment ejected from a glacier is collectively referred to as till, which is essentially synonymous with the historical term drift.

Icesheets and glaciers "retreat" when the rate of melting at their perimeters exceeds the rate of ice accumulation at their centers. When these rates are exactly balanced, the edge of the icesheet will remain in the same place and continue to eject till, building up a long linear pile along the perimeter. Such a pile at the maximum extent of an icesheet is called a terminal moraine. Accumulations that are deposited during standstills in the course of the icesheetís retreat are called recessional moraines.

If till is ejected from the icesheet directly onto the landscape, it collects in an unlayered deposit and is composed of every conceivable grain size, all mixed together. All moraine (there are many forms) has this unstratified, unsorted character. However, if till is washed out of an icesheet in a meltwater stream and is brought into a glacial lake, the resulting deposit is both layered and sorted (i.e., the various types of kame). Smaller sediment grains remain suspended in the water column longer and are carried further from the icesheet source. As a result, clays accumulate several miles from the ice front and large boulders may be found immediately next to it, with a more or less continuous gradation in size between these two extremes. 

PINNACLE RANGE GEOLOGY

When the "Ontario lobe" of the "Laurentian" icesheet reached a standstill over Rochester 10,000 years ago, it was depositing debris into a body of water that Fairchild called "Glacial Lake Dana". Most of the glacial lakes were named for famous geologists. Consequently, the lower half of the Pinnacle Range consists of stratified sands and gravels, as described by Dryer, and is, as he claimed, a kame deposit. It is part of a longer feature that extends westward, which is sometimes called the "Rochester-Albion moraine".

Fairchild described the Pinnacle Range as a "hybrid structure" called a kame-moraine, because the hills, although stratified at the base, have an unstratified "crown" that is in many places full of large boulders. Fairchild reasoned that the icesheet must have retreated northward a short distance from the kame delta it had built into Glacial Lake Dana. A brief re-advance of the icefront then reached the crest of the ridge and remained there for a relatively brief period of time, leaving a thin "icing" of moraine atop the layered "cake" of the kame. 

The final retreat from the Pinnacle kame-moraine was associated with a drop in the lake level, and the water body in front of the icesheet became "Glacial Lake Dawson". The icefront was then located roughly along the present shoreline of Lake Ontario. The shoreline of Glacial Lake Dawson was below the ridge on which Mt. Hope Avenue and East and West Henrietta roads are built. This height of land separates the modern Genesee watershed from the Irondequoit Creek drainage. Lake Dawson filled the Irondequoit Creek watershed, but a smaller glacial water body called Glacial Lake Scottsville remained in the Genesee Valley between Rochester and Avon. The dam that created the lake was the Albion-Rochester (kame-)moraine, which crossed the valley at the present site of the River Campus of the University of Rochester. 

The icesheet was apparently melting very rapidly as it built up what became the Pinnacle Range; whole sections of the icefront were collapsing. The evidence for this is the abundance of kames and kettles along the length of the range. While kame-deltas and kame terraces are linear features (the latter collect between a retreating ice sheet and a valley wall and can be found in the Finger Lakes region), kames, essentially, are actually conical hills. The term kame refers to the mode of formation and their stratified appearance rather than the gross form of the feature. 

When a boulder or a till-rich portion of ice is exposed on top of the icesheet as it is disgorged, it will absorb heat from the sun and re-radiate it into the surrounding ice, melting it, and creating a pond or lake on the surface of the glacier. This is a positive feedback process, because as more ice melts, more till in uncovered, washed into the pond and more heat is absorbed and re-radiated. Therefore, this water-filled depression accumulates stratified sediments, just as a lake on land would do. Eventually, all of the surrounding glacial ice melts away leaving the accumulated sediment as a stratified pile sitting on the landscape. 

The rapid collapse of an ice front has been observed at the termini of modern glaciers. Blocks of ice the size of houses or larger fall off the ice front and disappear into the soupy till, becoming partially or completely buried. Insulated by the surrounding sediment and its own bulk, such an ice mass may take decades or even centuries to melt. As the ice volume slowly disappears, any overlying sediment settles downward creating a depression called a kettle.

Because both land forms are associated with episodes of rapid melting, they are often found together in what are known as kettle and kame terrains. The Mendon Ponds area is one local example and consists of very large kettles and kames. The northern portion of Mt. Hope Cemetery is another. 

GEOLOGY OF MT. HOPE CEMETERY 

Till and Moraine

Icesheets have a parabolic profile; they thin very gradually toward their perimeters and then have very steep edges. The Laurentide Ice Sheet is estimated to have been 14 km (9 miles) thick at the center. Imagine the roughly circular icesheet with three concentric zones around its center. The center area was the zone of accumulation. In the second zone, the base of the icesheet was primarily eroding the Earthís surface, picking up sediment and absorbing it into the plastic, moving mass. But in the outer third of its radius, the icesheet began to deposit its till load. In most places, it simply plastered it across the landscape (ground moraine), but where the base of the icesheet moved quickly, it sculpted the ground moraine into long distinctly cigar-shaped hills called drumlins. If the shape of the hill is more obscure, then it may be referred to as a "drumlinoid".

Mt. Hope Cemetery is divided by Grove Avenue into two distinct physiographic districts. South of Grove Avenue, the ground is flat or slopes in smooth planes toward the west. Mt. Hope Avenue comes down off the kame-moraine from Highland Avenue and stays on the high ground that forms that divide between the watersheds of the Genesee River and Irondequoit Creek. This low ridge is one of several south of Rochester that are oriented slightly east of north and are composed of what Fairchild called "drumlinoid till."

Because drumlins are deposited as the icesheet advances, they will be underneath any kame or glacial lake deposits that are deposited as the ice retreats. This is the case over much of Rochester, Brighton, and Henrietta, where sediments deposited in Glacial Lakes Warren, Dana, Dawson, and Iroquois blanket earlier glacial features, softening their outlines and creating a smoothly rolling or nearly flat landscape. The Pinnacle kame-moraine is one of the most prominent interruptions in this muted topography. 

Gravel Pits and Natural Depressions

Immediately north of Grove Avenue in the cemetery, there is a steep rise in the north slope of the kame-moraine that may be a wave-cut surface formed at the shore of Glacial Lake Scottsville. All 

of the cemetery between this rise and its northern boundary is a classic and dramatic kame and kettle terrain. The kames are so numerous that some are partially overlapping, perhaps representing supra-glacial ponds that initially were separate and then melted the intervening ice away before being set down into a composite pile on the land.

Because Mount Hope was set aside as a burial ground in 1838, it was less subject to commercial quarrying than the rest of the Pinnacle Range. In 1923, H. L. Fairchild published a summary of his research on the "Rochester kame-moraine" in the Proceedings of the Rochester Academy of Science. At age 73, Fairchild used this paper to wax elegiac about the vanished landscape along the Pinnacle Range. When he began observing and photographing the area in the early 1890s, most of the range, except for the Pinnacle itself, was dotted with kettle ponds. In the first 20 years of the 20th century, when the Ellwanger & Barry horticultural nursery turned into a real estate company and began building houses on the north slopes of the hills, the kettle ponds were filled in. 

Depressions carved into the hillsides of the Pinnacle Range outside of Mt. Hope are often gravel pits. The Fairchild Collection at the University of Rochesterís Rare Books Division includes a large number of photographs that show laborers, horses, and carts standing in front of enormous excavations, particularly at Cobbs and Pinnacle hills. However, the most easily observed gravel pit is "The Gully" in Highland Park. This depression extends from the intersection of Doctors Road and Reservoir Avenue to behind Lamberton Conservatory. 

Most natural depressions are created by the erosive action of running water. In order to carry the sediment away and create the hole, water must run downhill. The gravel pits and kettles are two types of depressions not created by running water, so both are typically missing a low spot at their periphery that marks the exit of the water that ordinarily excavates the hole in the first place. 

Kame Sediments 

The most difficult area to interpret in the cemetery lies north of Grove Avenue, west of Indian Trail Avenue and south of Patriot Hill (Section R). The topography is uneven and includes many breaks in slope that are modifications made to produce more level areas for graves and for the passage of roads. However, the entire area may have been an early 19th century gravel pit. If the slope once led more evenly down to the riverside, it has been modified in the recent past by the construction of dormitories and tennis courts immediately north and west of the cemetery fence, which has left a steep excavated face just beyond the fence. Let us traverse this area from Grove Avenue along Glen Avenue. 

One of the few places in the cemetery where the underlying glacial sediments are exposed is in the cut made by Glen Avenue as it drops down from Grove Avenue. The sediments visible there are very fine, well sorted sands. This is evidence that they were deposited into standing water several hundred yards from the ice front. Were it possible to follow these layers at Glen Avenue laterally, one would observe coarsening of the sediment grains northward and fining toward silts and clays to the south. Soil has crept down the cut made by the road, obscuring the geology that was probably revealed by the excavation. At present, the sands can best be seen among the exposed tree roots along the embankment. No sediment layering is visible here because of decades of creep and soil formation. In order to see the strata, one would have to dig a trench into the hillside, which would be rather frowned upon, to say the least. 

The presence of a retaining wall along Cedar Avenue to the east of the intersection with Glen Avenue (Section MM) indicates that sediment has been removed from the natural slope in order to construct Cedar Avenue. Westward along Cedar, there is a break in slope to the north (toward the dormitories) that is covered in sumac trees. This has apparently been excavated to flatten the area to the north for graves added in the 1890s. 

As you follow Glen Avenue northward from Pine Avenue to Buell Avenue (between Sections M and W), you pass out of this depression into the kame area. A small kame lies between West Avenue and Glen Avenue (Section R). An even smaller kame lies between West Avenue and Patriot Hill (Section B). Both of these have the characteristic steep, conical shape of kames. A larger, more irregular kame is traversed by Linden Avenue (Section A). The northern boundary of the kame area is Maple Avenue. 

The most easily discerned kame in Mt. Hope Cemetery can be seen immediately behind the north gatehouse (Section E) at the north entrance off Mt. Hope Avenue. The steep conical shape has been little altered by roadbeds or walking trails, and no other kame material is draped over it. A more complicated and more disrupted group of kames is traversed by Hillside, Ravine, Hope, and Indian Trail avenues (Sections G, K, F, and I). 

Kettles

Sylvan Waters, surrounded by Hope, Cedar, and Dell avenues, is perhaps the most visible and unambiguous kettle in the cemetery. Its slopes have been modified; a terrace has been cut midway between the grade of the surrounding roads and the waterís edge. The rough-hewn cairn of mortared dolomite stones in the middle of the pond was once a working fountain. But in spite of these anthropogenic modifications, the original inverted conical shape of a typical kettle is apparent. There is a shallower dry kettle just west of Sylvan Waters toward the junction of Cedar and Dell avenues. It, too, has been terraced, but here it has been done to provide a flat area for graves. Another apparent dry kettle can be seen south of the intersection between Indian Trail and Dell avenues. 

Whether this last is actually a kettle depends upon the uncertain nature of the ridge traversed by Indian Trail Avenue. Steven Thomas, former director of the Rochester Museum and Science Center, hypothesized that the ridge is an esker. Geologist Warren Upham mistook the entire Pinnacle Range for an esker in the 1890s. Eskers, like kames, formed during the retreat of the icesheet. But unlike kames, which formed on top of or at the perimeter (kame deltas or kame terraces) of the ice sheet, eskers formed in tunnels through the ice that were cut by meltwater. The meltwater was heavily laden with the sediment that had been absorbed by the plastic glacial ice as it crept down from the north. The tunnels, therefore, filled with sediment faster than the meltwater could expand their diameter. Once the tunnel was filled with sediment, it was abandoned and remained as a sinuous, coarsely stratified deposit within the icesheet. When the surrounding ice melted away, river-shaped ridges were left snaking across the landscape. 

Thomas' hypothesis is tenable for a least four reasons. First, it is oriented roughly perpendicular to the ice front, which is generally true of eskers. Second, the Mt. Hope kames are draped over the ridge, which indicates that they were deposited later. Kames develop on top of the icesheet and so would be deposited over subglacial features. Third, historical records document the existence of a wetland east of the ridge (Section L). The ridge upon which Indian Trail Avenue sits evidently blocked the path of water draining from uplands to the south and east and toward the Genesee River to the west. The wetland was drained by tunneling under the ridge. Finally, the name "Indian Trail" is drawn from local legend that would suggest that the ridge was not constructed, but was pre-existing from, as they say, time immemorial. 

The only sure way to discover the origin of the ridge is to excavate it, which is unlikely to be undertaken just to satisfy curiosity. In such cases, investigators must wait for chance to intervene. If one of the larger oaks along the ridge is knocked over in a storm, wrenching the roots from the steep, unstable hillside, then a hole of sufficient size may be created for geological study. Construction projects to regrade roads or replace drainage pipes also might provide a look inside. If the Indian Trail Avenue ridge is indeed an esker, it would be constructed of coarsely stratified layers of poorly sorted sediments. 

Glacial Erratics

The sediment exposed among the roots of wind-thrown trees on the northern slope below Indian Trail Avenue is full of glacial cobbles. These stones have a distinct shape regardless of their lithology (rock type) that is a result of being dragged across the land in the maw of a moving mass of ice several kilometers (more than a mile) thick. Because they are wrested from their point of origin and deposited sometimes hundreds of miles away, sometimes perched in rather unlikely places, these stones are referred to as erratics. 

If you pick one up, you can see that there are three relatively flat facets to each one. Two facets are generally narrower than the third. All come to a point at one end of the long axis of the stone; these cobbles are generally oblong. The opposite end of the long axis is generally a rounded surface. The overall appearance is that of a stubby boat with a distinct keel, pointed prow, and rounded stern. The broader facet is the top of the boat with the two narrower sides forming the keel. This distinctive shape is found in pebbles and in boulders as large as houses. 

The Henry A. Ward monument at the junction of Indian Trail and Cedar avenues in Section G is itself a glacial erratic collected in Georgian Bay, Canada by Ward himself. The conglomerate boulder is studded with red jasper cobbles and has the distinctive boat shape of an erratic. Conglomerates are sedimentary rocks that include a mixture of sediment grain sizes; some of the grains are up to several centimeters across. 

If erratics come from a moraine, and by definition they have not been in running water, then the facets tend to be distinct, coming to relatively sharp edges. If they have been picked up and moved in glacial meltwater streams, they tend to become more rounded and begin to approach the smooth ovate shape of river stones. The cobbles in windthrows (areas where trees are uprooted by wind, exposing the cobbles) below Indian Trail Avenue are slightly smoothed, suggesting that they were transported in moving water for some distance before being deposited. This lends further credence to the hypothesis that the narrow ridge upon which Indian Trail Avenue sits is an esker. There are two well known eskers in Mendon Ponds County Park. The western one is actually truncated by the New York State Thruway immediately east of the Clover Street overpass. 

Many of the cobbles that are found in windthrows have exotic lithologies. The rocks with the most distant provenance are probably the gneisses, which are derived from the Canadian Shield in Ontario. Gneisses have the same mineralogy as granites (quartz, feldspar, and mica), but granites are igneous rocks and cool from a molten state. Gneisses are metamorphic rocks, that is, they are derived by subjecting sedimentary and igneous rocks to enormous amounts of heat and pressure, often at great depths below the Earthís surface. This mode of creation causes the axes of minerals in gneisses to be oriented in a consistent direction. This is particularly apparent in the dark micas. In contrast, the minerals in granites are generally randomly oriented. 

The other exotic metamorphic rock that is hard enough to survive being dragged beneath an icesheet from Ontario, Canada to New York State is quartzite. As its name suggests, quartzite is composed almost entirely of the mineral, quartz, which causes them to be a milky white or slightly pink color. Marble, the other common white metamorphic rock, is not hard enough to survive long-distance transport beneath an icesheet. In addition, marble is chemically susceptible to dissolution in mildly acid conditions, as is evident by the poor condition of marble monuments exposed to urban air pollution like acid rain. Glacial meltwater, laden as it is with silicate minerals, can have a rather low acid pH. 

Local Bedrock

Most of the rocks that can be found in Mt. Hope Cemetery, either lying on the ground or used to build the retaining walls and other structures in the cemetery, are of local origin. All of the bedrock of western New York is of sedimentary origin, which is to say that it was deposited as layers of sediment in shallow tropical seas that covered this area repeatedly between roughly 550 and 320 million years ago. The sediment was hardened into rock by being buried deep within the Earth. Over the past 30 million years or so, it has been uplifted more in the north than in the south and the layers are therefore tilted from three to five degrees to the south. These slabs of bedrock underlie the entire western portion of the state from the Catskill Mountains out into the Midwest and the southern part of Ontario, Canada. Because they are tilted ("dipping" is the geological term) to the south and eroded down, they are exposed in broad east-west bands through the Southern Tier of New York State, the Finger Lakes, and the Ontario Lake Plain. The oldest (deepest) rocks are exposed along the shores of Lake Ontario and the youngest at the Pennsylvania border. 

The most abundant stones in Mt. Hope Cemetery and other area cemeteries (aside from the monuments) are derived from the Lockport and Medina Groups, which formed during the Silurian Period (435 to 410 million years ago). A group is a package of sedimentary rocks that are genetically related, which is to say that they represent a series of depositional environments that existed subsequent to one another in the geological past over a particular area. Groups are composed of formations, each formation consisting of sediment that accumulated in a distinct environment in the past. The Medina Group includes a sandstone called the Grimsby Formation, which represents an ancient beach environment. The Lockport Group includes a series of formations that consist of a rock type called dolostone. These were originally deposited as reefs and shells composed of calcium carbonate (limestone), but during their burial and transformation into rock, they were infused with magnesium-rich pore waters, which altered their molecular structure. Many of the boulders that emerge from excavations in the Rochester area are pieces of the Penfield Dolomite formation. This represents an ancient reef, and the rounded coral heads can often be seen in the boulders. In an unaltered state, the corals are composed of adjacent hexagonal tubes, giving them the appearance of globular honeycombs. But the infusion of magnesium disrupted the crystal structure of the limestone, leaving the coral heads looking like cancerous cabbages. 

The Silurian reefs eroded into adjacent lagoons (imagine something like the modern Bahamas archipelago), filling them with layered carbonate mud. These lagoonal limestones were often used as building stone in the Rochester area before the Erie Canal made importation of exotic stone economically practical. The retaining wall for the cemetery along Mt. Hope Avenue is composed largely of Lockport (gray) and Medina (red) stone. The pillars that mark the corners of Highland Park were originally composed of gray Lockport dolomite, but reconstructed pillars have been faced with a fine-grained gray granite. 

SUMMARY

Before the last ice age, the landscape of Mount Hope Cemetery simply did not exist. The land likely sloped smoothly upward from the lowlands near the present location of the New York State Thruway to the ridge of the Niagara escarpment, upon which the city of Rochester is built. But between 10,000 and 9,000 B.P., the latest ice sheet paused in its final northward retreat and deposited sediment into a lake of meltwater ponded between its southern edge and the land rising south of Avon. This was to become the bulk of the Pinnacle kame-moraine, a stratified bulwark of sand and silt that stretched for several miles between Brighton and Albion. At the location of Mt. Hope Cemetery, in particular, the front of the ice sheet seems to have collapsed in a rapid and dramatic manner. This collapse left that part of the range a confused mass of overlapping kame hills and kettle depressions that early settlers would one day find economically useless and later citizens would find extremely picturesque. 

The geologic history of the cemetery location divides it neatly into two very different sections. The northern, more picturesque section is composed of the kame-moraine itself, with its chaos of kames and kettles. The southern, more orderly section is laid out on the smooth expanse of a former glacial lake bottom. The northwestern section has been altered from its natural state by excavations, perhaps related to the building of a railroad embankment, perhaps for more distant purposes, but in general, we find the land much as the ice sheet left it, only covered by soil, grass, trees, and the monuments to the dead. 

ADDITIONAL READING

Fairchild, H. L., 1895. The kame-moraine at Rochester, NY. American Geologist, v. 16, pp. 39-51.

Fairchild, H. L., 1923. The Pinnacle Hills, or the Rochester kame-moraine. Proceedings of the Rochester Academy of Science, v. 6, pp.141-194.

Fairchild, H. L., 1928. Geologic Story of the Genesee Valley and Western New York. Published by the author. Distributed by Scrantomís, Inc. 

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Last revised:  May 5, 2005