Hopewell Furnace National Historic Site 

Geologic Resources Inventory Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2010/214 

National Park Service 

U.S. Department of the Interior 

Natural Resource Program Center 
THIS PAGE: 

In the late 18th and 19th centuries, iron furnaces 

like Hopewell Furnace laid the foundation for 

the transformation of a fledgling nation into an 

industrial powerhouse. 

ON THE COVER: 

This view shows the restored “furnace group” 

structures of Hopewell Furnace National Historic 

Site. The stone structure in the middle is the 

actual furnace. The cast house is the white structure to the right; the wheel house and bridge 

house are to the left. 

National Park Service photographs. 
Hopewell Furnace National Historic Site 

Geologic Resources Inventory Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2010/214 

Geologic Resources Division 

Natural Resource Program Center 

P.O. Box 25287 

Denver, Colorado 80225 

June 2010 

U.S. Department of the Interior 

National Park Service 

Natural Resource Program Center 

Ft. Collins, Colorado
The National Park Service, Natural Resource Program Center publishes a range of reports that 

address natural resource topics of interest and applicability to a broad audience in the National 

Park Service and others in natural resource management, including scientists, conservation and 

environmental constituencies, and the public. 

The Natural Resource Report Series is used to disseminate high-priority, current natural 

resource management information with managerial application. The series targets a general, 

diverse audience, and may contain NPS policy considerations or address sensitive issues of 

management applicability. 

All manuscripts in the series receive the appropriate level of peer review to ensure that the 

information is scientifically credible, technically accurate, appropriately written for the 

intended audience, and designed and published in a professional manner. This report received 

informal peer review by subject-matter experts who were not directly involved in the 

collection, analysis, or reporting of the data. 

Views, statements, findings, conclusions, recommendations, and data in this report do not 

necessarily reflect views and policies of the National Park Service, U.S. Department of the 

Interior. Mention of trade names or commercial products does not constitute endorsement or 

recommendation for use by the U. S. Government. 

Printed copies of this report are produced in a limited quantity and they are only available as 

long as the supply lasts. This report is available from the Geologic Resources Inventory website 

(http://www.nature.nps.gov/geology/inventory/gre_publications.cfm) and the Natural 

Resource Publications Management website (http://www.nature.nps.gov/publications/

NRPM). 

Please cite this publication as: 

Thornberry-Ehrlich, T. 2010. Hopewell Furnace National Historic Site: geologic resources 

inventory report. Natural Resource Report NPS/NRPC/GRD/NRR—2010/214. National Park 

Service, Ft. Collins, Colorado. 

NPS 376/103722, June 2010 

ii NPS Geologic Resources Division 
HOFU Geologic Resources Inventory Report iii

Contents

List of Figures................................................................................................................ iv

Executive Summary ....................................................................................................... v

Acknowledgements...................................................................................................... vi

Credits........................................................................................................................................................................ vi

Introduction ................................................................................................................... 1

Purpose of the Geologic Resources Inventory ...............................................................................................................1

Park Setting .................................................................................................................................................................1

Geologic Setting ..........................................................................................................................................................1

History of Hopewell Furnace.........................................................................................................................................2

Geologic Issues .............................................................................................................. 6

Water Issues ................................................................................................................................................................6

Disturbed Lands and Mineral Development ..................................................................................................................7

Preservation of the Natural Environment ......................................................................................................................7

Slope Processes............................................................................................................................................................7

Paleontological Resources (Fossils)................................................................................................................................8

Geologic Features and Processes................................................................................ 10

Geologic Influences on the Furnace and Smelting Iron................................................................................................10

Geologic Influences on Biological Resources...............................................................................................................11

Cambrian-Triassic Unconformity .................................................................................................................................11

Mount Pleasure..........................................................................................................................................................12

Map Unit Properties .................................................................................................... 15

Geologic History .......................................................................................................... 21

Precambrian Mountain-Building and Extension (prior to 542 million years ago)...........................................................21

Paleozoic Events (542 to 251 million years ago)..........................................................................................................21

Mesozoic Extension (251 to 65.5 million years ago)....................................................................................................22

Cenozoic Landform Evolution (65.5 million years ago until today)...............................................................................23

Glossary........................................................................................................................ 27

Literature Cited............................................................................................................ 31

Additional References ................................................................................................. 34

Appendix A: Overview of Digital Geologic Data....................................................... 35

Attachment 1: Geologic Resources Inventory Products CD
iv NPS Geologic Resources Division 

List of Figures

Figure 1. Map of Hopewell Furnace National Historic Site.................................................................................................3

Figure 2. Physiographic provinces of Pennsylvania ............................................................................................................4

Figure 3. Mesozoic rift basins...........................................................................................................................................5

Figure 4. Hopewell Furnace .............................................................................................................................................5

Figure 5. French Creek flows through Hopewell Furnace National Historic Site..................................................................8

Figure 6. Water was needed to drive the water wheel powering the blast machinery........................................................9

Figure 7. Geologic map of units within the boundaries of Hopewell Furnace National Historic Site....................................9

Figure 8. Diagram of a typical cold-blast furnace............................................................................................................12

Figure 9. Map of iron furnaces and ironworks surrounding Hopewell Furnace ................................................................13

Figure 10. Geologic column of rock units exposed within Hopewell Furnace National Historic Site. .................................14

Figure 11. Geologic time scale .......................................................................................................................................24

Figure 12. Evolution of the landscape in southern Pennsylvania......................................................................................25

Figure 13. Triassic extension of the Newark Basin...........................................................................................................26
HOFU Geologic Resources Inventory v

Executive Summary

This report accompanies the digital geologic map for Hopewell Furnace National Historic 

Site in Pennsylvania, produced by the Geologic Resources Division in collaboration with its 

partners. It contains information relevant to resource management and scientific research.

This document incorporates preexisting geologic information and does not include new data 

or additional fieldwork.

Hopewell Furnace National Historic Site is located 

within the greater Schuylkill River watershed of 

southeastern Pennsylvania. Forested valleys and hills 

characterize the landscape, and disturbed forest 

covers three quarters of the site. Elevations within the 

park range from 140 m (460 ft) to 280 m (920 ft). 

French Creek State Park and Pennsylvania State 

Game lands surround the site on three sides, creating 

a large protected area in the densely populated 

Pennsylvania Piedmont.

Mark Bird founded the Hopewell Furnace operation

in 1771, choosing the site because of its abundance of 

local natural resources necessary for such an 

enterprise—water, topographic relief, forests (for 

charcoal), local limestone (for flux and building 

materials), and iron ore deposits. The furnace 

operated from 1771 to 1883, transforming raw 

materials into iron, and fashioning the molten iron 

into various necessities. Ore was supplied from three 

local mines. Hopewell Furnace National Historic Site 

commemorates the enterprising spirit of the industrial 

age and educates the public about this pivotal time in 

American history.

The site is in the western Piedmont physiographic 

province near the junction of three sections: 

Gettysburg-Newark Lowland, Piedmont Upland, and 

Piedmont Lowland. The rocks in this area range from 

metamorphosed and deformed Precambrian mafic to 

felsic gneisses and Paleozoic metasediments to the 

gently tilted, much younger sedimentary strata of the 

Mesozoic rift basins. Within the park itself, Triassicage gray to red sandstone, mudstone, shale, and 

conglomerate outcrop near Cambrian quartzitebearing units across a 300-million year unconformity. 

These rocks may contain fossils and hold clues to the 

geologic history of the area. Thus, the site’s geologic 

resources and their role in history can be an integral 

part of interpretation for park visitors. 

Geology provides the foundation of the ecosystem. 

Understanding the geology of southeastern 

Pennsylvania enhances understanding of the unique 

relationship between geology and the environment. 

Geologic processes initiate complex responses that 

give rise to rock formations, topographic expression, 

surface and subsurface fluid movement, and soils. At 

Hopewell Furnace, human land use disturbances are 

part of the site’s historical relevance. Furnace 

operators sculpted the landscape, logged the 

surrounding forest slopes, impounded and diverted 

local streams, and imported ore and flux from 

surrounding mines and quarries. The following issues 

have a high level of resource management importance

at Hopewell Furnace National Historic Site: 

• Water issues. The park protects the headwaters area 

of French Creek. This creek is impounded 

upstream to form Hopewell Lake. Ongoing water 

quality studies seek to understand the impacts of 

heavy metal concentrations resulting from iron 

smelting. 

• Disturbed lands and mineral development. 

Regionally, abandoned and inactive mines and 

quarries pose safety, environmental, and health 

problems. These features could interrupt the 

regional hydrologic regime and could threaten park 

resources. Remediation of mine- and industryaffected areas in southeastern Pennsylvania is a 

cooperative effort.

• Preservation of the natural environment. The 

geologic features and processes on display at the 

park lend themselves to interpretation and 

educational opportunities. The park also strives to 

relate the history of the area to the geologic 

resources responsible for the location being chosen 

for the iron furnace.

• Slope processes. Slopes throughout the park area 

can be prone to mass wasting. Boulder fields and 

talus deposits form primarily during freeze-thaw 

cycles and from plant root wedging.

• Paleontological resources. Fossils can record the 

depositional environment and paleoclimate, as well 

as provide information on post-burial conditions. 

Fossils have not yet been found in the park. 

However the geologic units in the park are known 

to contain fossils elsewhere. Locally known fossils 

and trace fossils include Skolithos burrows.

The rocks within and surrounding the park record a 

long geologic history—from the Proterozoic Eon 

through the Quaternary Period—that involves the 

intermittent uplift of mountains, tectonic forces of 

compression and extension, inundation of oceans, 

accretion of land masses, and long periods of erosion 

and deposition. This geologic history is part of the 

story at Hopewell Furnace National Historic Site.

The glossary on page 27 contains explanations of 

many technical terms used in this report, including 

terms used in the Map Unit Properties Table.
vi NPS Geologic Resources Division 

Acknowledgements

The Geologic Resources Inventory (GRI) is one of 12 inventories funded by the National 

Park Service Inventory and Monitoring Program. The GRI is administered by the 

Geologic Resources Division of the Natural Resource Program Center.

The Geologic Resources Division relies heavily on 

partnerships with institutions such as the U.S. 

Geological Survey, Colorado State University, state 

geologic surveys, local museums, and universities in 

developing GRI products.

Special thanks to: Ron Sloto (U.S. Geological Survey)

for his comments and suggestions regarding water 

quality and mining history in the Hopewell Furnace 

area. Frances Delmar and Rebecca Ross (Hopewell 

Furnace NHS) provided images and information of 

the park.

Credits

Author

Trista Thornberry-Ehrlich (NPS-Colorado State 

University)

Review

William Kochanov (Pennsylvania Geological Survey)

Jason Kenworthy (NPS Geologic Resources Division)

Editing

Bonnie Dash (Envirocal)

Digital Geologic Data Production

Georgia Hybels (NPS Geologic Resources Division)

Stephanie O’Meara (NPS-Colorado State University)

Digital Geologic Data Overview Layout Design

John Gilbert (NPS-Colorado State University)

Phil Reiker (NPS Geologic Resources Division)
HOFU Geologic Resources Inventory 1

Introduction

The following section briefly describes the National Park Service Geologic Resources 

Inventory and the regional geologic setting of Hopewell Furnace National Historic Site.

Purpose of the Geologic Resources Inventory 

The Geologic Resources Inventory (GRI) is one of 12 

inventories funded under the National Park Service 

(NPS) Inventory and Monitoring Program. The GRI,

administered by the Geologic Resources Division of the 

Natural Resource Program Center, is designed to 

provide and enhance baseline information available to 

park managers. The GRI team relies heavily on 

partnerships with institutions such as the U.S. Geological 

Survey, Colorado State University, state geologic surveys, 

local museums, and universities in developing GRI 

products.

The goals of the GRI are to increase understanding of the 

geologic processes at work in parks and to provide sound 

geologic information for use in park decision making. 

Sound park stewardship requires an understanding of 

the natural resources and their role in the ecosystem. 

Park ecosystems are fundamentally shaped by geology. 

The compilation and use of natural resource information 

by park managers is called for in section 204 of the 

National Parks Omnibus Management Act of 1998 and in 

NPS-75, Natural Resources Inventory and Monitoring 

Guideline. 

To realize these goals, the GRI team is systematically 

conducting a scoping meeting for each of the 270 

identified natural area parks and providing a parkspecific digital geologic map and geologic report. These 

products support the stewardship of park resources and 

are designed for nongeoscientists. Scoping meetings 

bring together park staff and geologic experts to review 

available geologic maps and discuss specific geologic 

issues, features, and processes. 

The GRI mapping team converts the geologic maps 

identified for park use at the scoping meeting into digital 

geologic data in accordance with their Geographic 

Information Systems (GIS) Data Model. These digital 

data sets bring an interactive dimension to traditional 

paper maps. The digital data sets provide geologic data 

for use in park GIS and facilitate the incorporation of 

geologic considerations into a wide range of resource 

management applications. The newest maps contain 

interactive help files. This geologic report assists park 

managers in the use of the map and provides an overview 

of park geology and geologic resource management 

issues.

For additional information regarding the content of this 

report and current GRI contact information please refer 

to the Geologic Resources Inventory web site 

(http://www.nature.nps.gov/geology/inventory/).

Park Setting

Hopewell Furnace National Historic Site sits within the 

French Creek drainage (designated as a Scenic River by 

the State of Pennsylvania in 1982) in the greater 

Schuylkill River watershed of southeastern Pennsylvania 

(fig. 1). Tributaries to the creek include Spout Run and 

Baptism Creek. Forested valleys and hills characterize 

the landscape at the site. Disturbed forest types cover 

three quarters of the land, recording the site’s history of 

furnace operations that used trees to make charcoal. 

Elevations within the park range from a high of 280 m 

(920 ft) in the north to a low of 140 m (460 ft) where 

French Creek exits the park to the east. The larger 

French Creek State Park (3,035 ha [7,500 ac]) and 

Pennsylvania State Game lands surround the historic site 

on three sides, creating a large protected area in the 

densely populated Piedmont of southeastern 

Pennsylvania (Inners and Fergusson 1996; Glaser 2005).

Geologic Setting

Precambrian crystalline rocks, Lower Paleozoic 

metamorphosed sedimentary and sedimentary rocks, 

and Triassic sedimentary rocks underlie the landscape at 

Hopewell Furnace National Historic Site, directly 

controlling its highly irregular topography (Inners and 

Fergusson 1996). Relatively undeformed conglomerate 

and shale sit beneath the south-facing slope in the 

northern areas of the site. The Triassic Hammer Creek 

Formation contains quartz conglomerate and sandstone 

that is more resistant to erosion than the sandstone, 

siltstone, and mudstone of the Triassic Stockton 

Formation that sits below the lower areas throughout the 

center of the park (Podniesinski et al. 2005). As mapped 

by Bascom and Stose (1938), Cambrian-age Vintage 

Dolomite (a soluble carbonate rock) underlies the 

lowest-lying areas drained by French Creek and 

lowlands southeast of the village of Hopewell. The older 

geologic units in the Hopewell Furnace vicinity are 

faulted and deformed with varying degrees of 

metamorphism preserved in outcrop exposures. 

Precambrian gabbro and gneiss and erosion-resistant 

Cambrian quartzite crop out beneath the steepest 

topography in the southern reaches of the park (National 

Park Service 2009).

The geology influences soil patterns at Hopewell 

Furnace. Soils developed atop the Precambrian rocks 

tend to be deep and well drained, whereas soils along the 

major creeks are poorly drained. Soils tend to be very 

stony on conglomeratic substrates to the north (National 

Park Service 2009). 

Hopewell Furnace sits near the junction of two 

physiographic provinces—the Piedmont province and

the Valley and Ridge province—as described below 

(fig.2). More specifically, the park is near the junction of 
2 NPS Geologic Resources Division 

three subprovinces of the Piedmont province: the 

southern edge of the Gettysburg-Newark (Triassic) 

Lowland section, the Piedmont Lowland section, and the 

Piedmont Upland section. 

Piedmont Province

Encompassing the Fall Line westward to the Blue Ridge 

Mountains is the Piedmont physiographic province. The 

“Fall Line” (also known as “Fall Zone”) marks a 

transitional area at which the softer, less-consolidated 

sedimentary rocks of the Atlantic Coastal Plain to the 

east intersect the harder, more resistant metamorphic 

rocks to the west to form ridges, waterfalls, and rapids. 

Examples of the rapids formed by Piedmont rocks exist 

in the Potomac Gorge of Chesapeake and Ohio Canal 

National Historical Park (Maryland) and at Great Falls 

Park (Virginia). 

The eastward-sloping Piedmont formed through a 

combination of folds, faults, uplifts, and erosion. The 

resulting eastern landscape of gently rolling hills starts at 

an elevation of 60 m (200 ft), and becomes gradually 

steeper westward toward the western edge of the 

province to reach 300 m (1,000 ft) above sea level. The 

Piedmont Plateau is composed of hard, crystalline 

igneous and metamorphic rocks, such as schist, phyllite, 

slate, gneiss, and gabbro. Soils in the Piedmont Plateau 

are highly weathered and generally well drained.

A series of Triassic-age extensional (“pull-apart”) basins 

are superposed on the Piedmont. Normal faulting 

formed these basins during Mesozoic crustal extension. 

The faults opened basins (grabens), and these basins 

were rapidly filled with roughly horizontal layers of 

sediment. Examples include the Frederick Valley in 

Maryland, the Gettysburg-Newark Basin in Pennsylvania

(fig. 3), and the Culpeper Valley of Northern Virginia. In 

general, depositional contacts define the western 

boundary of the basins with the Piedmont Plateau. 

Normal faults sharply define the western boundaries of 

the basins, west of which are the Blue Ridge and Valley 

and Ridge provinces. 

History of Hopewell Furnace

Hopewell Furnace provides a fine example of a 19th

century rural American iron plantation. Mark Bird, the 

first ironmaster, founded the furnace in 1771. The 

plantation operated until 1883, transforming raw 

materials into molten iron to make the stove plates, 

plowshares, cook pots, shot, weights, and other articles 

necessary for living in 19th century America. Included in 

the products of Hopewell Furnace were armaments for 

the Continental forces during the Revolutionary War 

(Demer 2003).

Authorized as Hopewell Village National Historic Site on 

August 3, 1938 (during the Franklin Delano Roosevelt

presidential administration), and renamed as Hopewell 

Furnace National Historic Site on September 19, 1985, 

the site preserves the historic landscape of one of the 

nation’s early iron forge communities (Glaser 2005). In 

accordance with its Long Range Interpretive Plan, the 

overall themes of Hopewell Furnace National Historic 

Site are: 1) exemplifying the state of the iron-making 

industry in the nascent United States, an industry central 

to the growth of the nation; and 2) demonstrating a 

microcosm of the social, political, economic, and 

technological developments in America throughout 112 

years of the plantation’s operation, from the colonial 

period to the post-Civil War era (Hopewell Furnace 

National Historic Site 1993). 

A geologically relevant sub-theme involves the 

dependence of iron-making on the raw materials of the 

area (limestone, iron ore, hardwood forests, and 

waterpower), how that dictated the location of the iron 

plantation, and how the operation in turn altered the 

surrounding natural environment (Demer 2003).

The site covers approximately 343 ha (848 ac) southeast 

of Pottstown, spanning the boundary between Berks and 

Chester Counties. Among the historic structures at the 

site are a blast furnace, an ironmaster’s mansion, and 

numerous outbuildings (figs. 1 and 4). For further 

information on the purpose, history, and setting of the 

site, please consult the administrative history document 

by Glaser (2005) or the Hopewell Furnace National 

Historic Site website: http://www.nps.gov/hofu.
HOFU Geologic Resources Inventory 3

Figure 1. Map of Hopewell Furnace National Historic Site. National Park Service map.
4 NPS Geologic Resources Division 

Figure 2. Physiographic provinces of Pennsylvania. The map graphic shows the physiographic setting of Hopewell Furnace National Historic Site. The green circle marks the location of the 

park and historic site. The red lines indicate boundaries between major physiographic provinces. The black arrow locates the northern terminus of the Blue Ridge province. Graphic by Trista L. Thornberry-Ehrlich (Colorado State University) after Sevon (2000).
HOFU Geologic Resources Inventory 5

Figure 3. Mesozoic rift basins. Mesozoic rift basins are shown related to the structural patterns along the East Coast. Note how the trend 

of the basins is roughly parallel to the overall geologic trend of the surrounding physiographic provinces. Graphic by Trista L. 

Thornberry-Ehrlich (Colorado State University) after figure 1 in Root (1989).

Figure 4. Hopewell Furnace. The reconstructed wheel house is on the left, stone furnace in the center and reconstructed casting and 

moulding house on the right. National Park Service photograph reproduced in Glaser (2005). 
6 NPS Geologic Resources Division 

Geologic Issues

The Geologic Resources Division held a Geologic Resources Inventory scoping session for

Hopewell Furnace National Historic Site on June 22–24, 2004, to discuss geologic resources, 

address the status of geologic mapping, and assess resource management issues and needs. 

This section synthesizes the scoping results, in particular those issues that may require 

attention from resource managers. Contact the Geologic Resources Division for technical 

assistance.

Water Issues

French Creek flows through the heart of Hopewell 

Furnace National Historic Site (figs. 1 and 5). In 1982, 

the Commonwealth of Pennsylvania designated the 

waterway as a Scenic River due to its natural and scenic 

values. This creek and its tributaries, Spout Creek and 

Baptism Run, are primary natural resources at the park. 

Additional water resources include wetlands, numerous 

natural springs, flanking riparian zones and floodplains, 

and the underlying groundwater system (National Park 

Service 2009). 

The park’s waterways and their adjoining riparian 

habitats provide a vital sanctuary for many species of 

birds. Rivers and streams cut through the various rock 

layers, creating valleys, ravines, and gullies. Erosion and 

small-scale flooding occur along park waterways during 

seasonal storms and could threaten park infrastructure 

(GRI, scoping notes, 2004).

The surrounding natural lands provide buffers between 

the park and the increasing urban development in Berks 

and Chester Counties. Three Pennsylvania Natural 

Diversity Sites (Pine Swamp, Sixpenny Creek, and 

French Creek) are within or adjacent to Hopewell 

Furnace National Historic Site or French Creek State 

Park. Berks County identified these sites as having 

statewide significance for biodiversity protection 

(National Park Service 2009). Surrounding areas also 

pose concerns for park resource managers. Such 

concerns include the stability of and impacts to water 

quality from the earthen dam that impounds Hopewell 

Lake just upstream from the park’s western boundary 

(GRI, scoping notes, 2004). 

Damming of French Creek and other local streams began 

during the furnace operations of the early 19th century. 

The east head race and west head race were constructed 

to supply water to the furnace’s water wheel (figs. 1 

and 6). As part of the New Deal work relief programs of 

the 1930s, Civilian Conservation Corps workers 

constructed Hopewell Dam to impound Hopewell Lake, 

the space for which they also cleared.

National Park Service (1998) compiled and summarized

baseline water quality data for Hopewell Furnace and the 

surrounding area. The U.S. Geological Survey (USGS) 

and NPS Mid-Atlantic Inventory and Monitoring 

Network (MIDN) are currently conducting a water 

quality study along French and Baptism creeks within 

and near the park. The study focuses on understanding

heavy metal transport following the smelting of iron ore 

within the furnace (R. Sloto, USGS, personal 

communication, May 2010). The iron ores used at the 

Hopewell Furnace contained elevated concentrations of 

arsenic, cobalt, lead and other metals (R. Sloto, USGS, 

personal communication, May 2010). 

The underlying geology is a primary determinant on any 

groundwater flow system. In the Hopewell Furnace area, 

much of the groundwater is stored in weathered 

Triassic-age rock. Hydrogeologic models of similar rocks 

elsewhere in Pennsylvania characterize this as a complex, 

heterogeneous, multiaquifer system (Sloto and 

McManus 1996). The aquifer system can be envisioned 

as layers of gently tilting rocks of high permeability

separated by layers of rocks of relatively low 

permeability. In general, the more permeable rock layers 

are arkosic sandstones and conglomerates, whereas the 

siltstone and shale units tend to be softer and less 

permeable. Each layer has different hydrologic 

properties such as fractures, bedding planes, and joints to 

accommodate groundwater movement (Sloto and 

McManus 1996). In localized settings, a single fracture 

can control local groundwater flow, independent of the 

overall hydrogeologic structure (Schuller et al. 1982).

Also underlying the Hopewell Furnace area are 

Cambrian carbonate rocks, whose increased 

permeability along dissolved conduits could strongly 

influence the local hydrogeologic system.

The park’s water supply is from two groundwater wells 

(National Park Service 2009). One of these wells is a 

domestic well providing water to the Lloyd House, and is 

not connected to the rest of the park (R. Sloto, U.S. 

Geological Survey personal communication, May 26, 

2010). Understanding the hydrogeologic system at the 

park can provide information for resource management. 

Applied geophysical techniques provide valuable tools in 

observing hydrologic properties, characterizing 

groundwater flow systems, and detailing subsurface 

geology. Potential techniques include surface resistivity, 

magnetometer, shallow seismic, electric logging, and 

cross hole seismic (Emrich 1984). Additionally, streams 

integrate the surface runoff and groundwater flow of 

their watersheds—combining input from sources such as 

wind, surface runoff, groundwater, sewage outfalls, 

landfills, dredged fill dirt, and rainfall—thus providing a 

cumulative measure of the status of the watershed’s 

hydrologic system. Consistent measurement of these 
HOFU Geologic Resources Inventory 7

parameters is crucial to establishing baselines for 

comparison. 

Contact the NPS Water Resources Division (Fort 

Collins, Colorado) for technical assistance with water 

resource issues.

Disturbed Lands and Mineral Development

The rocks and mineral resources within and surrounding 

Hopewell Furnace National Historic Site have long 

attracted people. Copper mines and abundant iron 

forges attest to this interest. Iron ore mines provided raw 

materials for the furnace. Extensive quarrying of the 

Paleozoic limestones for flux in the furnace and building 

material left numerous scars on the landscape. In 1885, 

Davis Knauer (first president of the French Creek 

Granite Company, established in 1910) opened a quarry 

into Jurassic diabase near St. Peters, a few kilometers 

southeast of the park (R. Sloto, USGS, personal 

communication, May 2010). The diabase was polished 

for ornamental and architectural stone, which was 

marketed as “black granite” (Topinka 2005).

Three local mines (Hopewell, Jones, and Warwick), all 

outside of park boundaries, supplied ore for the 

Hopewell Furnace (R. Sloto, USGS, personal 

communication, May 2010). Most of the mining was 

accomplished via small open pits although several shafts 

exist. The mines are now on private and state lands. 

Some of the open pits are flooded (R. Sloto, personal 

communication, May 2010).

Abandoned and inactive mines and quarries outside the 

park boundaries still pose safety, environmental, and 

health issues to the greater Hopewell Furnace area. 

These features interrupt the regional hydrologic regime 

and could threaten the park’s soils, groundwater, and 

small streams and springs. Remediation of mine- and 

industry-affected areas in southeastern Pennsylvania is a 

cooperative effort. In addition to the National Park 

Service, agencies such as the U.S. Geological Survey, the 

Pennsylvania Department of Environmental Protection, 

and the Pennsylvania Environmental Council, as well as 

many local offices, are all contributing to environmental 

preservation and human health and safety (Anonymous 

2002). None of the three Hopewell area mines have been 

reclaimed (R. Sloto, USGS, personal communication, 

May 2010). 

Park interpreters aim to tie into the narrative of the park 

information about the surrounding areas, as they 

provided the materials necessary for the Hopewell 

Furnace processes of iron extraction, moulding, and 

casting (GRI, scoping notes, 2004). Though not 

contained within the boundaries of Hopewell Furnace 

National Historic Site, many of the surrounding map

quadrangles of interest contain quarries, mines, and 

shafts that could augment the story of the park, if 

captured in the digital geologic data for the park (GRI, 

scoping notes, 2004).

Preservation of the Natural Environment

The NPS views a cultural landscape as a geographic area 

containing both natural and cultural resources (Glaser 

2005). According to the park’s 1994 Resource 

Management Plan, one of the largest threats to the park is 

the impending loss of the rural environment and natural 

resources:

In its heyday, Hopewell Furnace was an industrial 

island in an agricultural sea; today [the area] is a 

small island of open space endangered by a rapidly 

rising sea level of residential and commercial 

development.

Though most visitors are interested in the historical 

context of the Hopewell Furnace National Historic Site 

landscape, the park provides an ideal outdoor classroom 

for earth science students (see Geologic Features and 

Processes section). It also protects a significant tract of 

intact forest in southeastern Pennsylvania (Glaser 2005). 

Issues can arise from the differing strategies of cultural 

and natural resource management. For example, a 

proposal for the restoration of a historic garden, creation 

of a viewshed, or development of landscaping could 

involve the removal of surrounding natural resources, 

installation of stabilization structures, or planting of 

exotics. The conservation of today’s natural beauty at 

Hopewell Furnace National Historic Site is somewhat 

compromised by the interpretation of an early industrial 

landscape that would have been utilitarian, nonaesthetic, and much disturbed (Glaser 2005).

Slope Processes

The resistant quartzites of the Cambrian Chickies 

Formation form rolling hills across the southern portion 

of the park (Podniesinski et al. 2005). The Chickies 

Formation also underlies the steep northern slopes and 

crest of Mount Pleasure along the western edge of the 

park (fig. 7; Appendix A) (Inners and Fergusson 1996).

Weathering and gravity-driven slope processes of the 

Chickies quartzite gives rise to a steep boulder field 

formation along the west-central edge of the park, which

stands as a testament to active slope processes 

(Podniesinski et al. 2005). Boulders of quartzite at this 

location, many with diameters of 1m (3 ft) or more, form 

a continuous blanket of talus that extends upslope more 

than 30 m (100 ft) to a jumbled and fractured bench of 

quartzite (Inners and Fergusson 1996). Freeze-and-thaw 

cycles or plant roots could wedge other blocks of rock 

loose from this formation and threaten resources and 

infrastructure downslope. However, the talus slope 

appears stable (R. Sloto, USGS, personal communication, 

May 2010).

Downcutting streams such as French and Baptism creeks

and other erosive agents created valleys, ravines, and 

gullies on the landscape at Hopewell Furnace National 

Historical Site. Weathering processes, both mechanical 

and chemical, have also weakened the underlying 

geologic units that include sandstone, siltstone, 

mudstone, and shale. Among these units are the Triassic 

Hammer Creek and Stockton formations, which are 
8 NPS Geologic Resources Division 

heterogeneous and include weak, clay-rich mudstones 

interlayered with resistant sandstones and 

conglomerates (fig. 7; Appendix A) (Inners and 

Fergusson 1996). Clay-rich units such as shale and 

mudstone can disintegrate or swell when they become 

water saturated, and are prone to fail when exposed on a 

slope, resulting in a slide or slump. Where a resistant 

layer such as a conglomerate or sandstone overlies a clayrich layer, mass wasting potential exists due to 

preferential erosion (undercutting) of the clay layer, 

leaving no support for the resistant layer on top. 

Unstable slopes within the park may fail, especially when 

saturated with water after seasonal rainfall events. 

Talus and colluvial deposits at the bases of slopes attest 

to mass movements in the past. Today, the processes of 

slope creep and slumping can threaten roads and trails 

throughout the park (GRI, scoping notes, 2004). Threedimensional investigations of colluvium could shed light 

on the exact nature of their formation, how they 

influence groundwater flow, and the potential for future 

movements. Such studies involve test pits and deep 

borings, observations on colluvial composition, layering, 

and degree of weathering, as well as permeability 

measurements (Layton et al. 2006).

Paleontological Resources (Fossils)

Fossils add to the understanding of the geologic history 

of the Piedmont province and Mesozoic rift basins in the 

Hopewell Furnace area. Certain fossils are useful in 

correlating units across time and space. Others offer 

clues about the depositional environment when they 

were alive. Still others provide post-burial information, 

including geochemical changes, deformational regimes, 

and changes in bedding orientation. Fossil resources, 

when present, require science-based resource 

management as directed by the 2009 Paleontological 

Resources Preservation Act (Public Law 111-11). The 

National Park Service is currently developing regulations 

associated with the Act (J. Brunner, Geologic Resources 

Division, personal communication, May 2010). Santucci 

et al. (2009) suggest strategies for monitoring in situ 

paleontological resources.

The NPS conducted a paleontological inventory from 

literature of known and potential fossil occurrences in 

Hopewell Furnace National Historic Site (Kenworthy et 

al. 2006). No formal, field-based paleontological 

resource inventories have been completed, and the park 

has no collections of paleontological material 

(Kenworthy et al. 2006).

Some of the geologic units located on park lands are 

known to contain fossils regionally (fig. 7). Heavy 

vegetative cover and deeply weathered bedrock preclude 

extensive outcrop exposure. The highly erosion-resistant 

quartzite of the Cambrian-age Chickies Formation 

contains the trace fossil Skolithos (worm-like burrows). 

At the western end of Mount Pleasure, blocks of the 

Chickies quartzite contain specimens of the conspicuous 

sediment-filled Skolithos tubes (Inners and Fergusson 

1996). The Triassic Stockton Formations outcrops 

within the park boundaries and regionally contains plant 

fossils, invertebrate body and trace fossils, mollusk 

fossils, fish and amphibian remains, and reptilian and 

dinosaurian body fossils and footprints, although none 

are known in the park (Kenworthy et al. 2006). 

Investigators have noted dinosaur footprints locally in 

sedimentary rocks of the Gettysburg-Newark Basin 

(GRI, scoping notes, 2004). Approximately 200-millionyear-old fossil dinosaur tracks are within rocks of the 

same age at the Limerick Nuclear Power Station, located 

approximately 16 km (10 mi) to the east of Hopewell 

Furnace (Inners and Fergusson 1996). Field-based

paleontological resource inventories at Hopewell 

Furnace National Historic Site may uncover similar 

resources within the park.

Figure 5. French Creek flows through Hopewell Furnace National Historic Site. Left: U.S. Geological Survey photograph by Ron Sloto. 

Right: Following a thunderstorm; National Park Service photograph courtesy Frances Delmar (Hopewell Furnace NHS).
HOFU Geologic Resources Inventory 9

Figure 6. Water was needed to drive the water wheel powering the blast machinery. The east head race (left; 1939 photo after retaining 

wall restoration) and west head race and flume (right; 2006 photo after reconstruction) were man-made structures that transported 

water to the wheel house. Their locations are indicated on figure 1. National Park Service photographs in Yocum (2008).

Figure 7. Geologic map of units within the boundaries of Hopewell Furnace National Historic Site. Unit gga is Precambrian banded mafic 

gneiss; unit gg is Precambrian graphitic felsic gneiss; unit CCh is Cambrian Chickies Formation; unit Trs is Triassic Stockton Formation; 

unit Trh is Triassic Hammer Creek Formation; unit Trhc is Triassic Hammer Creek conglomerate. The green line is the national historic site 

boundary. Note that Cambrian dolomite is missing from the mapped units, but was observed by the NPS along the lowest reaches of 

French Creek (National Park Service 2009) and mapped by Bascom and Stose (1938). Graphic from Podniesinski et al. (2005) with data 

from Miles et al. (2001). Refer to Appendix A for an overview of the digital geologic data for the park.
10 NPS Geologic Resources Division 

Geologic Features and Processes

This section describes the most prominent and distinctive geologic features and processes 

in Hopewell Furnace National Historic Site.

Geologic Influences on the Furnace and Smelting Iron

Underlying the historic site area are Precambrian to 

Cambrian metamorphic and sedimentary rocks, as well 

as Triassic-age mudstones, siltstones, sandstones, and 

conglomerates in gently tilted and folded beds

(Appendix A). Weathering and erosion of these rocks 

shaped the rolling hills and narrow valleys characteristic 

of the Hopewell Furnace area. French Creek flowed 

through a narrow valley between two forested hills 

(Mount Pleasure and Brush Hill) and frequently flooded, 

leaving marshy conditions that were unfavorable for 

farming but suitable for industrial purposes (Glaser 

2005).

In 1771, Mark Bird, the first ironmaster, chose to build 

an iron furnace in Union Township, Berks County, 

Pennsylvania due to the abundant natural resources (ore, 

limestone, and charcoal) in the area (O’Neill 1976; 

Demer 2003). Bird constructed the furnace against a 

hillslope, so it would be appropriately configured for the 

loading of iron ore, limestone, and charcoal (known as 

“charging”) and to take advantage of running water as a 

potential power source by funneling it downslope to a 

water wheel (figs. 6 and 8) (Inners and Fergusson 1996; 

Demer 2003; Glaser 2005). Limestone was used as a flux 

to fuse impurities from the ore, and it was mined from 

local quarries in Hopewell or imported from sources east 

of Morgantown.

The furnace is nearly 9 m (30 ft) high by 4 m (12 ft) deep 

by 4 m (12 ft) wide, and is composed of heavy limestone 

blocks lined with refractory sandstone. The furnace 

design incorporated three primary features: 1) an uppertapering interior chamber; 2) a tuyere (interior pipe), 

which supplies a blast of air; and 3) a small hole at its base 

that allows molten iron to flow (fig. 8). Taking advantage 

of the local topography, Bird used a water wheel to 

supply the stream of air to the tuyere to accelerate 

combustion and increase the interior temperature 

(Demer 2003).

The conversion of ore to viable iron is a time-consuming 

process. In the early 1800s, a typical half-hour charge 

required 15 bushels of charcoal, 400 to 500 pounds of 

iron ore, and 30 to 40 pounds of limestone flux (O’Neill 

1976). These substances had to be heated to 

temperatures of 2,600 to 3,000 °F to produce the 

chemical reaction (Fe2O3 + 3CO = 3CO2 + 2Fe), wherein 

iron oxide ore loses (via reduction) its oxygen atoms to 

carbon monoxide produced by the burning charcoal 

(Demer 2003). Once the iron was molten, the founder 

would extract the material, and moulders would create 

iron products using casting sand. At Hopewell Furnace, 

moulders used the green-sand process for smaller 

articles, and dry-sand or loam for larger castings. 

According to historic estimates, moulders formed and 

poured no fewer than 75,000 flasks to produce 

approximately 5,000 iron stoves at Hopewell Furnace 

(Demer 2003).

Iron Ore Mines

Early iron ore mining for the Hopewell Furnace was 

performed by open pit and bell pit mining (O’Neill 1976). 

Three local mines supplied iron ore to Hopewell 

Furnace: Warwick, Hopewell, and Jones mines. These 

mines were within three different ore bodies only a few 

kilometers from the furnace (fig. 9). The mines began as 

open-pit operations; however, as mining technology 

advanced, some regional mines such as the Warwick 

Mine developed shaft operations. Initially, it was 

common to extract high-grade ore (40 to 60 % iron was 

common); however, the quality of iron ore usually 

decreased as mining progressed (Lewis and Hugins 1983; 

Inners and Fergusson 1996). Magnetite (Fe3O4) was the 

primary iron-bearing mineral of the local ore, with 

accessory hematite (Fe2O3), calcite (CaCO3), and pyrite 

(FeS2). Examples of this ore exist in a rock pile adjacent 

to the furnace at the Hopewell Furnace National 

Historic Site (Inners and Fergusson 1996; Demer 2003). 

In 1926, a study detailed the presence of fine magnetite 

crystals, as well as some interesting quartz 

pseudomorphs after datolite in scraps of ore from the 

Hopewell mine (Vaux 1926). The iron ores originated as 

part of the “Morgantown pluton” (see “Geologic 

History” section). Accompanying this igneous intrusion 

were superheated, iron-rich gaseous and watery 

solutions that altered and/or replaced the surrounding 

rock (limestone or marble in this case), creating the iron 

ore that became the focal resource of Hopewell Furnace 

(Inners and Fergusson 1996). The Jurassic-aged diabase 

dikes mapped north of the park were also associated 

with the Morgantown pluton.

The Warwick Mine, located in Warwick Township, was 

the last major mine opened for ore extraction at 

Hopewell Furnace. It now sits within State Game Lands 

(north of State Route 23) and on private land (south of 

State Route 23). A total of five shafts—ranging in depth 

from 8 to 31 m (25 to 102 ft)—existed during the 120 

years of operation at Warwick Mine, although most of 

the mining was open pit or “bell pit” mining (R. Sloto, 

USGS, personal communication, May 2010)The

principal ore at the Warwick mine was gray magnetiterich rock.

The Hopewell Mine (also known as the Birdtown Mine) 

is contained within Pennsylvania State Game Lands on 

the south side of Thomas Hill (National Park Service

1997; Inners and Fergusson 1996). This mine consists of 

three open pits, three shafts and a slope (R. Sloto, USGS, 

personal communication, May 2010). It cuts through 

rocks of the Triassic Stockton Formation and Jurassic 

diabase. 
HOFU Geologic Resources Inventory 11

The Jones Mine was started in 1773 by Mark Bird and 

shut down in the early 1900s. This mine and the 

Hopewell Mine were the most crucial to Hopewell 

Furnace operations. Jones Mine is 120 m (400 ft) wide 

and approximately 60 m (200 ft) deep. It sat amidst 16 ha 

(40 ac) in Caernarvon Township between Elverson and 

Joanna (National Park Service 1997; Inners and 

Fergusson 1996). Today, the mine is flooded and located 

on private property (R. Sloto, USGS, personal 

communication, May 2010).

Geologic Influences on Human History

The 1968 establishment of an Environmental Study Area 

(ESA) at Baptism Creek partially focused on the 

interaction between human beings and nature, reviewing

the ecological background of the forested area and the 

impact of the furnace and charcoal pollution. Today, the 

park does not include the ESA in its interpretive efforts; 

however, the ESA helped to shape visitors’ 

understanding of the rural-industrial landscape at 

Hopewell Furnace (Glaser 2005).

The diversity of geologic phenomena in the Hopewell 

Furnace area can illustrate many geologic concepts in a 

learning environment. The concept of geologic time is 

readily accessible in the Precambrian- to Mesozoic-age 

rocks within and surrounding the park. Rocks and fossils 

indicate depositional environments and conditions of life 

in the distant past (Inners and Fergusson 1996; 

Kenworthy et al. 2006). The geologic structures in the 

area record several episodes of mountain building and 

continental rifting. The Triassic rocks within the park 

record a large rift basin superimposed on the Piedmont 

physiographic province as the eastern coast of the North 

American continent underwent extension following the 

mountain-building Alleghany orogeny. Periglacial 

conditions affected the area during the Pleistocene by 

changing the courses of rivers, causing floral and faunal 

migrations, wedging apart the rock units, and leaving vast 

talus deposits. Relating geology to human concerns such 

as floods, slope failures, iron ore mining, water pollution, 

limestone quarrying, waste management, and urban 

development would make the science meaningful to park 

visitors (Nikitina 2003). Relating geology and geologic 

processes to the history of the blast furnace and 

ironworks would lend deeper meaning to the human 

history of the area. 

One of the major goals of the park is to preserve the 

historical context of the area—including the recreation

of some of the village land use patterns (orchards and 

gardens) and structures, and the preservation and 

restoration of historic structures from the time of the 

furnace operation. Maintaining any historic landscape 

often means resisting natural geologic changes. Features 

such as streams naturally erode and meander. French 

Creek, vital to the cultural story of Hopewell Furnace, is 

part of a dynamic hydrogeologic system prone to change.

Geologic processes such as slumping, chemical 

weathering, block sliding, and slope creep are constantly 

changing the park landscape. Runoff erodes sediments 

from any open areas, carrying them down streams and 

gullies. Erosion naturally diminishes higher areas and fills 

in the lower areas, distorting the historical context of the 

landscape. Extensive mining, deforestation, manipulation of the stream system, and other land use practices 

(including urban development and farming) have 

changed the regional topographic expression.

Geologic Influences on Biological Resources

The geologic framework at Hopewell Furnace National 

Historic Site, including the underlying bedrock and 

resulting geomorphology, have greatly influenced the 

type and distribution of vegetation and ecology 

(Podniesinski et al. 2005). According to a 2005 

cooperative vegetation mapping study between the U.S. 

Geological Survey and the NPS, the thin, rocky, welldrained soils above the erosion-resistant bedrock of the 

northern slopes and southern hills of the park favor the 

development and growth of oak-dominated forests and 

woodlands. The less-resistant bedrock in the central 

areas of the park—including Triassic sandstone, 

mudstone, and siltstone—underlies deeper, richer soils 

that support mesic and wet forest vegetation. The lowslope valley areas favor forested seeps and shrub wetland 

assemblages. Along French Creek, poorly drained, finetextured alluvial deposits characterize the flat floodplain 

soils and support palustrine shrublands and forests 

(Podniesinski et al. 2005).

To operate the furnace for just one day required an acre 

of forest resources (Glaser 2005). Little to none of the 

original forest types remain in Berks and Chester 

Counties, due to the large-scale regional deforestation 

throughout the 18th and 19th centuries, as well as 

agriculture and pasture land use practices in support of 

the community at Hopewell Furnace (Podniesinski et al. 

2005). In 1985, Hopewell Furnace National Historic Site 

received funding for a biological study to identify plant 

communities for “historic scene restoration” (Glaser 

2005). In 1987, 504 species of vascular plants were 

documented in a vegetation study within park 

boundaries. Many of these species were invasive, but 

settlers might have introduced them during the historic 

furnace period. The NPS identified the need to research 

the specific species that should be considered part of the 

historic scene and judge the risks of allowing them to 

remain (National Park Service 2009). Geology, as a great 

influence on species distribution, merits particular notice 

in such research.

Cambrian-Triassic Unconformity

Hopewell Furnace National Historic Site contains 

interesting geological features called unconformities,

erosional surfaces between rock units of different ages 

(fig. 10). Among the most profound is the unconformity 

between the heavily deformed and metamorphosed 

Cambrian Chickies Formation (quartzite) and the 

relatively undeformed, mixed sedimentary strata of the 

Triassic Stockton Formation. This tangible gap in 

geologic history spans more than 300 million years 

(Inners and Fergusson 1996; W. Kochanov, Pennsylvania

Geological Survey, written communication, 2010). 

Another profound unconformity exists between the 

metamorphosed, approximately 1-billion-year-old 
12 NPS Geologic Resources Division 

Precambrian gneisses (among the oldest rocks in 

Pennsylvania) and the Cambrian Chickies Formation. 

Another important juxtaposition of rocks of different 

ages is the intrusive contact between Jurassic diabase 

dikes and surrounding Triassic-age country rock. 

Resistant diabase forms Millers Point and Monocacy Hill 

in the Hopewell Furnace area. These ridges are along the 

edge of the Morgantown pluton (Inners and Fergusson 

1996).

Mount Pleasure

Mount Pleasure is a 270-m-high (885-ft-high) hill located 

south of Hopewell Lake on the western edge of 

Hopewell Furnace National Historic Site. This feature 

contains the oldest geologic units in the park area

(Appendix A). Erosion-resistant Cambrian quartzites of 

the Chickies Formation underlie the steep northern 

slopes and crest of the hill, whereas Precambrian banded 

mafic gneisses support the gentler eastern slopes. Several 

pervasive faults cut and displace the rock units of Mount 

Pleasure in a haphazard manner (Inners and Fergusson 

1996).

Figure 8. Diagram of a typical cold-blast furnace. By 1852 pistons inside “blowing tubs” were used supply the blast of air to the furnace. 

Diagram by Trista Thornberry-Ehrlich (Colorado State University) after NPS graphic (waterwheel) and WITF (Harrisburg, PA)/Courtney Howell 

graphic (furnace) available at http://explorepahistory.com/displayimage.php?imgId=4266 (accessed June 2010). 
HOFU Geologic Resources Inventory 13

Figure 9. Map of iron furnaces and ironworks surrounding Hopewell Furnace. The three locations marked with a purple X indicate the 

mines that supplied iron ore to Hopewell Furnace. Graphic by Trista L. Thornberry-Ehrlich (Colorado State University) after an 

unnumbered figure by the NPS from Lewis and Hugins (1983).
14 NPS Geologic Resources Division 

Figure 10. Geologic column of rock units exposed within Hopewell Furnace National Historic Site. Graphic by Trista L. Thornberry-Ehrlich 

(Colorado State University) after an unnumbered figure by Inners and Fergusson (1996).
HOFU Geologic Resources Inventory 15

Map Unit Properties

This section identifies characteristics of map units that appear on the Geologic Resources 

Inventory digital geologic map of Hopewell Furnace National Historic Site. The

accompanying table is highly generalized and for background purposes only. Grounddisturbing activities should not be permitted or denied on the basis of information in this

table. 

Geologic maps facilitate an understanding of Earth, its 

processes, and the geologic history responsible for its 

formation. Hence, the geologic map for Hopewell 

Furnace National Historic Site provided information for 

the “Geologic Issues,” “Geologic Features and 

Processes,” and “Geologic History” sections of this 

report. Geologic maps are two-dimensional 

representations of complex three-dimensional 

relationships; their color coding illustrates the 

distribution of rocks and unconsolidated deposits. Bold 

lines that cross or separate the color patterns mark 

structures such as faults and folds. Point symbols 

indicate features such as dipping strata, sample localities, 

mines, wells, and cave openings. 

Incorporation of geologic data into a Geographic 

Information System (GIS) increases the usefulness of 

geologic maps by revealing the spatial relationships 

among geologic features, other natural resources, and 

anthropogenic features. Geologic maps are indicators of 

water resources because they show which rock units are 

potential aquifers and are useful for finding seeps and 

springs. Geologic maps are not soil maps, and do not 

show soil types, but they do show parent material—a key 

factor in soil formation. Furthermore, resource managers 

have used geologic maps to make connections between 

geology and biology; for instance, geologic maps have 

served as tools for locating sensitive, threatened, and 

endangered plant species, which may prefer a particular 

rock unit. 

Although geologic maps do not show where earthquakes 

will occur, the presence of a fault indicates past 

movement and possible future seismic activity. Similarly, 

map units show areas that have been susceptible to 

hazards such as landslides, rockfalls, and volcanic 

eruptions. Geologic maps do not show archaeological or 

cultural resources, but past peoples may have inhabited 

or been influenced by depicted geomorphic features. For 

example, alluvial terraces may have been preferred use 

areas and formerly inhabited alcoves may occur at the 

contact between two rock units.

The geologic units listed in the following table 

correspond to the accompanying digital geologic data. 

Map units are listed in the table from youngest to oldest. 

Please refer to the geologic timescale (fig. 11) for the age

associated with each time period. The table highlights 

characteristics of map units such as: susceptibility to 

erosion and hazards; the occurrence of paleontological 

resources (fossils), cultural resources, mineral resources, 

and caves or karst; and suitability as habitat or for 

recreational use. Some information on the table is

conjectural and meant to serve as suggestions for further 

investigation.

The GRI digital geologic maps reproduce essential 

elements of the source maps including the unit 

descriptions, legend, map notes, graphics, and report. 

The following references are the sources for the GRI 

digital geologic data for Hopewell Furnace National 

Historic Site:

Berg, T.M., A. D. Glover, S. I. Root, W. E. Edmunds, D. 

M. Hoskins, W. D. Sevon, A. R. Geyer, D. B. 

MacLachlan, A. A. Socolow. 1980. Geologic map of 

Pennsylvania. Scale 1:250,000. 4th ser., PA DCNR Map 

1. Bureau of Topographic and Geologic Survey.

Miles, C. E., T. G. Whitfield (compilers). 2001. Bedrock 

geology of Pennsylvania. Scale 1:250,000. Digital 

dataset extracted from Geologic map of Pennsylvania. 

4th ser., PA DCNR Map 1. Bureau of Topographic and 

Geologic Survey. 

The GRI team implements a geology-GIS data model 

that standardizes map deliverables. This data model 

dictates GIS data structure including data layer 

architecture, feature attribution, and data relationships 

within ESRI ArcGIS software, and increases the overall 

utility of the data. GRI digital geologic map products 

include data in ESRI personal geodatabase and shapefile 

GIS formats, layer files with feature symbology, Federal 

Geographic Data Committee (FGDC)-compliant 

metadata, a Windows help file that contains all of the 

ancillary map information and graphics, and an ESRI 

ArcMap map document file that easily displays the map 

and connects the help file directly to the map document.

GRI digital geologic data are included on the attached 

CD and are available through the NPS Data Store

(http://science.nature.nps.gov/nrdata/).
HOFU Geologic Resources Inventory Report 16

Map Unit Properties Table: Hopewell Furnace National Historic Site

Colored rows indicate geologic units mapped within Hopewell Furnace NHS.

Age Map Unit

(Symbol) Unit Description Erosion 

Resistance

Suitability for 

Infrastructure Hazards PaleontologicalResources

Cultural 

Resources Karst Issues Mineral Resources Habitat Recreation GeologicSignificance

QUATERNARY

Trenton Gravel 

(Qt) 

Unit includes some alluvium and swamp 

deposits, contains gray or reddish-brown 

gravelly sand interbedded with sand, clay, 

and silt beds. Crossbeds present locally.

Very low

Avoid stream 

edge/riparian and 

wetland areas for 

heavy 

development, 

especially for 

wastewater 

treatment 

facilities due to 

proximity to 

water and high 

permeability.

Unit is associated 

with stream banks 

and riparian zone 

areas, and may be 

unstable if exposed 

on a slope or water 

saturated.

May contain ice age 

and modern 

remains.

May contain 

remains from 

historic events 

and 

settlements.

None. Sand, clay, 

silt, gravel.

Unit supports 

riparian 

habitats, and 

marshlands.

Unit is suitable 

for light 

recreation 

unless at a 

stream edge or 

wetland.

Unit records 

modern 

geomorphological 

changes in the park 

area landscape.

TERTIARY

Pensauken and 

Bridgeton 

Formations, 

undifferentiated

(Tpb)

Bryn Mawr 

Formation

(Tbm)

Tpb contains dark reddish-brown 

feldspathic quartz sand beds with 

interlayered fine gravel and some clay and 

silt. Tbm consists of gravelly sand and silt in 

reddish-brown high-level terrace deposits. 

Very low

Avoid most 

terrace deposits 

for heavy 

development due 

to instability of 

slopes and high 

permeability.

Unconsolidated 

nature of the units 

render them 

susceptible to mass 

wasting on steep to 

moderate slopes.

May contain plant 

fragments.

Terrace areas 

may contain 

traces of 

Native 

American 

campsites.

None. Sand, clay, 

silt, gravel.

Unit supports 

riparian 

habitats and 

well-drained 

soils.

Suitable for 

most recreation 

unless high 

slopes are 

present.

Units record 

history of erosion 

and deposition 

throughout the 

Tertiary.

CRETACEOUS

Patapsco(?) 

Formation

(Kp)

Unit is intensely colored, variegated, ironrich clay with some isolated interbedded 

sand.

Low

Variations in 

bedding, 

sediment, and 

degree of 

cementation may 

render unit 

unstable on 

slopes; generally 

suitable for most 

development.

Clay-rich massive 

bedded layers may 

spall in large blocks 

when unit is exposed 

on slope; susceptible 

to slumps and slides.

May contain 

Cretaceous age 

fossils.

None 

documented. None. Sand, clay.

Supports 

eastern 

hardwood 

forests 

regionally.

Suitable for 

most recreation 

unless exposed 

on slopes.

Widespread unit 

records Cretaceous 

depositional 

environment.

JURASSIC

Sedimentary strata 

at Jacksonwald and 

Aspers

(Js)

Diabase

(Jd)

Js is arkosic sandstone with some gray to 

black shale and limestone interbeds, ripplecross-laminated siltstone, and boulder 

conglomerate. Jd consists of medium- to 

coarse-grained tholeiite in dikes, sheets, and 

scant flows. Individual bodies vary in 

titanium content and presence of 

plagioclase phenocrysts. 

Moderate to 

high

Variations in rock 

type and degree of 

cementation may 

render unit 

unstable on 

slopes.

Jd may form resistant 

ridges that are prone 

to rockfall when 

undercut and/or 

weathered.

Js is fossiliferous.

Diabase was 

popular 

building stone.

Iron ore for 

Hopewell 

Furnace.

Limestone 

units are 

prone to 

dissolution.

Iron Ore. 

Labradorite, 

pyroxene, 

plagioclase 

phenocrysts 

(cm-size), 

diabase.

Jd weathers 

to support 

iron-, and 

magnesiumrich 

substrates.

Suitable for 

most recreation 

unless heavily 

altered or 

fractured.

Iron ore utilized at 

Hopewell Furnace 

associated with 

Morgantown 

pluton and 

intrusion of Jd. Jd

includes the dark

gray York Haven 

Diabase and the 

younger Rossville 

Diabase.

TRIASSIC

Brunswick 

Formation

(TRb)

Limestone 

fanglomerate 

(TRfl)

Quartz 

fanglomerate 

(TRfq)

TRb is primarily reddish-brown mudstone, 

siltstone, and shale with some green and 

brown interbedded shale. Some red and 

dark gray argillite interlayers near the base. 

TRfl is yellowish-gray to medium gray 

quartz matrix with limestone and dolomite 

pebbles, cobbles, and fragments. Some 

shale-clast beds are locally interlayered. 

TRfq contains a reddish-brown sandy 

matrix with well-rounded quartzite pebbles, 

cobbles, and rare boulders. 

Moderate

Heterogeneous 

nature of units 

may render them 

unstable on 

slopes.

Unit is prone to 

rockfall where 

weathered shale lies

beneath resistant 

sandstone ledges or 

where limestone has 

dissolved beneath 

overlying rock layers.

May contain 

Triassic age fossils.

None 

documented.

Limestone 

cobbles in 

TRfl may 

dissolve 

away 

creating 

voids and 

compromise 

unit 

integrity.

None 

documented.

Units 

weather to 

create myriad 

substrates.

Suitable for 

most recreation 

unless heavily 

weathered and 

friable.

TRb spans the 

Jurassic-Triassic 

boundary.
Colored rows indicate geologic units mapped within Hopewell Furnace NHS.

HOFU Geologic Resources Inventory Report 17

Age Map Unit

(Symbol) Unit Description Erosion 

Resistance

Suitability for 

Infrastructure Hazards PaleontologicalResources

Cultural 

Resources Karst Issues Mineral Resources Habitat Recreation GeologicSignificance

TRIASSIC

Hammer Creek 

Formation

(TRh)

Lockatong 

Formation

(TRl)

Hammer Creek 

conglomerate

(TRhc)

TRh contains quartzose sandstone, 

siltstone, and mudstone that appear gray 

and pale red in outcrop with fine- to coarsegrained textures. TRl is dark gray to black, 

thickly bedded argillite. Lenses and layers of 

thin-bedded black shale, impure limestone, 

and calcareous shale present locally. TRhc

is composed of interbedded cobble and 

pebble quartz conglomerate with red 

sandstone. 

Moderate

Suitable for most 

development 

unless highly 

fractured, 

weathered, or 

undercut on a 

slope.

Weathered 

mudstone or 

dissolved limestone 

underlying more 

resistant sandstone 

or argillite can create 

rockfall hazards.

May contain 

Triassic age fossils.

None 

documented.

Impure 

limestone 

layers are 

susceptible 

to 

dissolution 

and may 

compromise 

integrity of 

units.

Sandstone. None 

documented.

Unit is fine for 

most recreation 

unless heavily 

weathered on 

slopes.

Units record 

deposition within a 

Triassic rift basin of 

varying depth.

TRIASSIC

Stockton 

Formation

(TRs)

Stockton 

conglomerate

(TRsc)

TRs contains light gray to buff, coarsetextured arkosic sandstone, with some 

reddish-brown to purple sandstone, 

siltstone, and mudstone interbeds. TRsc

contains cobbles of quartz in a sandy, 

poorly sorted matrix with some 

conglomeratic sandstone present locally. 

Moderate

Heterogeneous 

nature of units 

may render them 

unstable on 

slopes.

Units form 

alternating ridges 

that may be prone to 

rockfall and 

landslides, especially 

where resistant 

sandstone layers are 

underlain by 

weathered red 

shales.

May contain 

Triassic age fossils.

None 

documented.

None 

documented

.

Sandstone. None 

documented.

Conglomeratic 

outcrops may 

attract climbers.

Units record 

deposition and 

reworking within a 

Triassic rift basin.

ORDOVICIAN

Martinsburg 

Formation

(Om)

Hamburg sequence 

rocks

(Oh)

Shale and 

Graywacke of 

Hamburg sequence 

(Ohsg)

Limestone of 

Hamburg sequence 

(Ohl)

Om contains dark gray to gray shale and 

slightly metamorphosed slate. Oh includes 

greenish-gray, purple, and maroon shale, 

siltstone, and graywacke with some flysch 

beds containing some of unit Om. Ohsg

consists of shale with conspicuous zones of 

graywacke. Ohl is thick-bedded limestone 

of the Hamburg sequence.

Moderate

Avoid dissolved 

units for 

development of 

wastewater 

treatment 

facilities;

weathered units 

may fail on slopes.

Unit is prone to 

rockfall where 

weathered shale is 

beneath resistant 

sandstone ledges or 

where limestone has 

dissolved beneath 

overlying rock layers.

May contain 

Ordovician age 

fossils.

Slate may have 

been locally 

quarried.

Unit Ohl is 

susceptible 

to 

dissolution 

and may 

undermine 

stability of 

overlying 

units.

Slate. Cave habitat.

Dissolved caves 

and cavities may 

attract attention.

Units record deep 

water marine 

depositional 

environment.

ORDOVICIAN

Cocalico 

Formation

(Oco)

Jacksonburg 

Formation

(Ojk)

Annville Formation 

(Oan)

Oco includes gray phyllitic shale, maroon 

shale, and siltstone with silty siliceous 

interbeds. Some argillaceous and quartzose

sandstones present locally. Ojk contains 

dark gray, shaly limestone with slaty 

cleavage. Some medium- to thick-bedded 

limestone is present in basal sections. Oan

consists of light gray, massive-bedded, 

limestone. Unit is calcium rich and mottled 

in the basal layers. 

Moderate

Avoid heavily 

dissolved units for 

development due 

to weakness of 

friable textures.

Limestone cements 

are prone to 

dissolution and may 

compromise 

outcrops of Ojk.

May contain 

Ordovician age 

fossils.

None 

documented.

Limestone 

layers and 

units are 

susceptible 

to 

dissolution,

forming 

caves, 

sinkholes, 

and cavities.

Sandstone, 

slate.

Oan

weathers to 

produce Carich 

substrates.

Cave-bearing 

units may attract 

attention.

Oco has 

allochthonous and 

autochthonous 

elements.
Colored rows indicate geologic units mapped within Hopewell Furnace NHS.

HOFU Geologic Resources Inventory Report 18

Age Map Unit

(Symbol) Unit Description Erosion 

Resistance

Suitability for 

Infrastructure Hazards PaleontologicalResources

Cultural 

Resources Karst Issues Mineral Resources Habitat Recreation GeologicSignificance

ORDOVICIAN

Beekmantown 

Group

(Ob)

Ontelaunee 

Formation

(Oo)

Epler Formation 

(Oe)

Rickenbach 

Formation

(Ori)

Stonehenge 

Formation

(Os)

Ob includes Oo, Oe, Ori, and Os. Oo is 

light to dark gray dolomite with very fine to 

medium crystalline textures; interlayered 

light gray limestone; and interbedded 

nodular, dark gray chert beds at the base. 

Oe includes light gray limestone with finegrained textures interlayered with gray 

dolomite. Some coarsely crystalline lenses 

are present locally. Ori contains medium to 

dark gray coarsely crystalline dolomite in 

the basal beds topped by medium to light

gray fine crystalline dolomite. Chert lenses, 

interbeds, and nodules are present locally. 

Os includes medium light gray to medium

gray, fine crystalline, massive limestone with 

some dark, siliceous layers and 

conglomeratic beds.

Moderate

Avoid heavily 

dissolved units for 

heavy 

development due 

to weakness of 

friable textures;

dissolved units are 

inherently porous,

and thus do not 

act as effective 

filters for 

wastewater.

Resistant chert 

nodules and beds 

pose rockfall hazard 

when surrounding 

limestone and 

dolomite dissolve 

preferentially.

Os has fossil 

fragments in 

discrete lenses.

Chert nodules 

may have 

provided tool 

material to 

Native 

Americans.

Interlayered 

limestone 

and 

dolomite are 

susceptible 

to 

dissolution.

Limestone, 

dolomite.

Unit may 

dissolve to 

form cave 

habitats and 

produce Caand Mg-rich 

substrates.

Dissolved caves 

and cavities may 

attract attention.

Widespread thick 

unit that shows 

facies changes 

geographically, 

recording shifting 

depositional 

environments.

ORDOVICIAN AND CAMBRIAN

Conestoga 

Formation

(OCc)

OCc contains light gray, thinly bedded 

contorted impure limestone with shaly 

partings. Conglomeratic layers present at 

base of unit. Locally metamorphosed to 

phyllite. 

Moderate

Unit weathers 

easily to sand,

which may render 

it too permeable 

for septic systems 

or too unstable 

for heavy 

development.

Unit is associated 

with rockfalls and 

slumps when 

exposed on slopes;

alternating resistant 

and weaker layers 

are prone to fail if 

undercut. Black shale 

units may contain 

arsenic that could be 

released to 

groundwater and 

soils.

May contain 

CambrianOrdovician age 

fossils.

Scant chert 

nodules may 

have provided 

tool material 

for Native 

Americans.

Impure 

limestone 

layers may 

partially 

dissolve and 

compromise 

integrity of 

unit.

Pink marble 

locally.

Unit 

underlies 

deep sandy, 

well-drained

soils.

Unit is friable

and may be 

unstable base for 

trails on slopes.

Unit spans 

Cambrian to 

Ordovician 

boundary.

CAMBRIAN

Richland 

Formation

(Cr)

Allentown 

Formation

(Cal)

Millbach 

Formation

(Cm)

Elbrook Formation 

(Ce)

Cr contains gray dolomite with some oolitic 

beds and medium gray limestone and dark

gray oolitic chert present locally. Cal is 

medium to medium dark gray, thick-bedded 

interlayered dolomite and impure 

limestone. Some chert stringers and nodules 

present locally with oolitic and stromatolitic 

calcareous siltstones at the base that 

weather to orange-brown. Cm includes 

pink to white and gray limestone and finely 

laminated crystalline dolomite. Ce is 

microcrystalline limestone with dolomite 

and metamorphosed layers of phyllite and 

marble. 

Moderate to 

moderately 

high for 

metamorphic 

layers

Units are suitable 

for most 

development 

unless highly 

dissolved and/or 

fractured.

Units may be 

associated with karst 

hazards if dissolution 

is prevalent. When 

undercut, units pose 

rockfall hazards.

Stromatolites in Cal

and Cm.

Chert nodules 

may have 

provided tool 

material for

Native 

Americans.

Interlayered 

limestone 

and 

dolomite are 

susceptible 

to 

dissolution.

Marble, 

limestone.

None 

documented.

Units may 

attract caver 

attention and 

provide cave 

habitats.

Units contain 

evidence of life 

along a Cambrianaged sea.

CAMBRIAN

Leithsville 

Formation

(Clv)

Buffalo Springs 

Formation

(Cbs)

Lower (Middle?) 

Cambrian rocks, 

undivided

(Cul)

Zooks Corner 

Formation

(Czc)

Clv contains medium to dark gray 

crystalline dolomite that weathers to light

yellowish-brown and gray. Unit is massive 

with some oolitic, pink to gray, mottled 

chert, thin shale and dolomitic shale 

interbeds with scattered sand grains. Cbs

contains light pinkish-gray limestone and 

dolomite with fine to coarse crystalline 

textures. Numerous siliceous and clay-rich 

laminae are present. Cul includes tectonic 

slices of Czc, Cl, Ck, Cv, Ca, Cah, and Ch. 

Czc includes medium gray dolomite with 

fine crystalline textures and interlayered 

siliceous to argillaceous stingers. 

Moderate

Heterogeneous 

nature of units 

may render them 

unstable on 

slopes, but 

suitable for most 

light 

development.

Limestone units may 

be associated with 

karst dissolution and 

processes, creating 

voids that may cause 

failure.

Stromatolites in 

Cbs near the top of 

the unit.

Chert nodules 

may have 

provided tool 

material for

Native 

Americans.

Interlayered 

limestone 

and 

dolomite are 

susceptible 

to 

dissolution,

forming 

caves, 

sinkholes,

and smaller 

cavities.

Dolomite, 

limestone.

Units 

weather to 

form myriad 

substrates 

that support 

many types of 

forests.

Units are 

suitable for most 

recreation 

unless heavily 

dissolved or 

fractured; caves 

provide habitats 

for bats and 

other fauna.

Cul is arranged in 

tectonic slices, 

recording the 

depositional 

environments and 

tectonic history of 

the area. Units 

contain evidence of 

life along a 

Cambrian-aged sea.
Colored rows indicate geologic units mapped within Hopewell Furnace NHS.

HOFU Geologic Resources Inventory Report 19

Age Map Unit

(Symbol) Unit Description Erosion 

Resistance

Suitability for 

Infrastructure Hazards PaleontologicalResources

Cultural 

Resources Karst Issues Mineral Resources Habitat Recreation GeologicSignificance

CAMBRIAN

Ledger Formation 

(Cl)

Kinzers Formation 

(Ck)

Vintage Formation 

(Cv)

Cl contains massive pure dolomite with 

some siliceous grading near the center of 

the beds. Unit appears light gray and 

mottled in outcrop. Ck consists of dark 

brown shale, gray to white spotted 

limestone, and marble in the lower beds, 

and sandy friable limestone in the upper 

beds. Cv is dark gray argillaceous dolomite 

with knotty textures and light gray marble 

in the basal layers locally.

Moderate

Units are suitable 

for most 

development 

unless highly 

dissolved and/or 

fractured.

Units weather to 

form friable, porous 

rocks that are 

unstable and may fail 

easily.

May contain 

Cambrian age 

fossils.

None 

documented.

Limestone 

and (to a 

lesser 

extent)

dolomite are 

susceptible 

to 

dissolution.

Marble.

Units 

weather to 

well-drained 

sandy soils 

with 

abundant 

clay clasts.

Units are 

suitable for most 

recreation 

unless steep 

slopes are 

present; caves 

may attract 

attention.

Units record 

oscillating 

Cambrian marine 

and nearshore 

depositional 

environments.

CAMBRIAN

Antietam and 

Harpers 

Formations, 

undivided

(Cah)

Antietam 

Formation

(Ca)

Hardyston 

Formation

(Cha)

Harpers Formation 

(Ch)

Chickies Formation 

(Cch)

Cah includes Ca and Ch. Ca consists of 

gray quartzite that appears buff in 

weathered outcrops. Cha includes light

gray, fine- to medium-grained quartzite and 

feldspathic sandstone in massive beds. 

Some quartz pebble conglomerate in basal 

beds. Ch contains dark greenish-gray 

phyllite and schist with thin quartzite 

interbeds. Cch consists of light gray massive 

quartzite and quartz schist, with some thin 

interlayered slate in the upper beds and 

conglomeratic beds at base. 

Moderate to 

very high for 

quartzite

Quartzite units 

cap ridges, and are 

suitable for most 

development 

unless highly 

fractured and/or 

exposed on steep 

slopes.

Units are associated 

with steep slopes and 

rockfall.

Skolithos in Cha

and Cch.

Quartzite 

provided 

building 

material 

regionally.

None 

documented

.

Quartzite.

Units 

underlie 

ridgetop, a 

well-drained 

habitat.

Resistant 

quartzite layers 

may attract rock 

climbers.

Units contain 

evidence of life 

along a Cambrianaged sea.

PROBABLY LOWER PALEOZOIC

Pegmatite

(Xpg)

Granitic gneiss and 

granite

(Xgr)

Mafic gneiss 

(Xmgh)

Ultramafic gneiss 

(Xu

Octoraro 

Formation

(Xo)

“Glenarm 

Wissahickon” 

formation

(Xgw)

Wissahickon 

Formation

(Xw)

Xpg contains coarse- to medium-grained

textures and granitic compositions. Xgr is 

metamorphosed granodiorite. Xmgh is 

dark, medium-grained gneiss of 

metamorphosed sedimentary rocks. Xu

includes serpentinite, steatite, and other 

altered peridotites and pyroxenites. Xo

consists of albite-chlorite schist, phyllite,

and hornblende gneiss. Granitized members 

are present locally. Xgw contains 

oligoclase-mica schist and lenticular 

amphibolite bodies of ocean floor basalt 

origin. Xw consists of oligoclase-mica 

schist, hornblende gneiss, augen gneiss, and 

some granitized quartz and feldspar rich 

members locally. 

Moderately 

high to high

Avoid areas of 

intense 

preferential 

compositional 

weathering (along 

foliation and 

between 

heterogeneous 

lenses). Suitable 

for most 

development 

unless highly 

weathered and/or 

fractured.

Rockfall hazard 

when unit is exposed 

on slope, especially if 

slope and dominant 

foliation planes are 

parallel.

None.

Xpg crystals 

may have 

provided trade

material.

None. Pegmatite, 

augen gneiss.

None 

documented.

Units are 

suitable for most 

recreation 

unless highly 

altered, cleaved, 

and/or 

fractured.

Units record early 

metamorphic 

history and 

depositional 

environments.
Colored rows indicate geologic units mapped within Hopewell Furnace NHS.

HOFU Geologic Resources Inventory Report 20

Age Map Unit

(Symbol) Unit Description Erosion 

Resistance

Suitability for 

Infrastructure Hazards PaleontologicalResources

Cultural 

Resources Karst Issues Mineral Resources Habitat Recreation GeologicSignificance

PRECAMBRIAN

Metadiabase

(md)

Anorthosite

(a)

Graphitic felsic 

gneiss

(gqm)

Felsic and 

intermediate gneiss 

(ggd)

Banded mafic 

gneiss

(gga)

Graphitic felsic 

gneiss

(gg)

Franklin Marble 

(fm)

Unit md is dark gray (greenish), finegrained altered diabase intrusions. Unit a

contains medium- to coarse-grained, 

bluish-gray plagioclase-rich rock with 

alteration minerals present locally. Unit 

gqm is medium-grained, dark gray, gneissic 

feldspar and quartz with some altered areas. 

Unit ggd contains medium-grained, pink to 

greenish-gray gneiss of quartz, feldspar, and 

mica. Unit gga interfingers with ggd and 

contains dark, fine- to medium-grained 

banded gneiss of sedimentary origin. Unit 

gg contains medium-grained gray gneiss 

and marble with quartz, feldspar, graphite,

and metamorphic minerals. Unit fm is 

coarse-grained, white, crystalline marble 

with disseminated graphite flakes.

High

Units are fine for 

most 

development 

unless heavily 

altered and/or 

fractured.

Rockfall hazard 

when units are

exposed on slope,

especially if slope 

and dominant 

cleavage direction 

are parallel.

None.

Marble may 

have provided 

quarry 

material.

Some 

dissolution 

of marble 

beds 

possible.

Gneiss, 

marble, 

graphite.

None 

documented.

Units are 

suitable for most 

recreation 

unless highly 

altered, cleaved, 

and/or 

fractured.

Units record 

accretion of distinct 

crustal blocks onto 

the North 

American 

continent. At 

approximately 1 

billion years old, 

these are some of 

the oldest rocks in 

Pennsylvania

PRECAMBRIAN

Felsic and 

intermediate gneiss 

(fgh)

Felsic gneiss

(fgp)

Hornblende gneiss 

(hg)

Mafic gneiss

(mgh)

Mafic gneiss (mgp); 

Felsic to mafic 

gneiss (gn)

Unit fgh contains light-appearing gneiss 

with medium-grained textures likely of 

sedimentary origin. Unit fgp consists of 

light, medium-grained silicic gneissic rocks. 

Unit hg is dark, medium-grained gneiss 

likely of sedimentary origin. Units mgh and 

mgp are similar, consisting of dark, 

medium-grained gneiss likely of 

sedimentary origin. Unit gn is quartz and 

light feldspar-bearing gneiss of mediumgrained texture and likely igneous origin.

High unless 

highly 

weathered

Avoid areas of 

intense 

preferential 

compositional 

weathering (along 

foliation and 

between 

heterogeneous 

lenses). Suitable 

for most 

development 

unless highly 

weathered and/or 

fractured.

Units may pose 

rockfall hazard if 

undercut or exposed 

on a slope.

None. None 

documented. None. Gneiss.

Mafic gneiss 

develops into 

Fe-, Mg-, and 

Ca-rich 

substrates 

that support 

myriad forest 

types.

Units are 

suitable for most 

recreation 

unless highly 

altered, cleaved, 

and/or 

fractured.

Metamorphosed 

rocks retain 

features and 

compositions 

characteristic of 

sedimentary and/or 

igneous origin. At 

approximately 1 

billion years old, 

these are some of 

the oldest rocks in 

Pennsylvania
HOFU Geologic Resources Inventory 21

Geologic History

This section describes the rocks and unconsolidated deposits that appear on the digital

geologic map of Hopewell Furnace National Historic Site, the environment in which 

those units were deposited, and the timing of geologic events that created the present 

landscape.

Hopewell Furnace National Historic Site (along with 

neighboring French Creek State Park) straddles the 

boundary between two sections of the Piedmont 

physiographic province: the Piedmont Upland and the 

Gettysburg Newark Lowland sections (Sevon 2000). The

geologic units in the mapped area within and 

surrounding Hopewell Furnace National Historic Site 

reflect a vast period of geologic history from the 

Proterozoic Eon through the Quaternary Period (figs. 10

and 11). The following text presents a regional 

perspective to connect the landscape and geology of the 

park to its surroundings.

Precambrian Mountain-Building and Extension

(prior to 542 million years ago)

During the mid-Proterozoic, approximately 1 billion 

years ago, the Grenville orogeny (mountain-building 

episode) resulted in the formation of a supercontinent 

that contained most of the continental crust in existence, 

including the cratonic masses of North America and 

Africa. Where land masses collided, high mountains 

formed. The metamorphic granites and gneisses in the 

core of the modern Blue Ridge Mountains, west of 

Hopewell Furnace, record the sedimentation, 

deformation, plutonism (intrusion of igneous rocks), and 

volcanism associated with this geologic period (Harris et 

al. 1997). Precambrian-age gneisses outcrop as small 

boulders east of Mt. Pleasure at Hopewell Furnace 

National Historic Site (Inners and Fergusson 1996; 

Brown 2002). Regionally, geologic units of this time 

include mafic to felsic gneisses, marbles, and metadiabase 

(Berg et al. 1980).

Following the Grenville orogeny, regional uplift and 

hundreds of millions of years of subsequent erosion 

beveled the landscape. Erosion of the Grenvillian 

highlands formed a basement surface for the younger 

rocks of the Appalachian Mountains (Southworth et al.

2001). Roughly 800 to 600 million years ago, extensional 

tectonic forces created rift zones and fissures through 

which massive volumes of basaltic magma extruded (fig. 

12A). The volcanic rocks covered the Precambrian 

crystalline basement in southern Pennsylvania. Now 

metamorphosed into greenstones, the Catoctin 

Formation outcrops in central Maryland at Catoctin 

Mountain Park (Thornberry-Ehrlich 2009).

Paleozoic Events (542 to 251 million years ago)

Extensional tectonic forces caused the supercontinent to 

break up and opened a sea basin that eventually 

expanded to become the Iapetus Ocean (fig. 12B). 

Depositional environments associated with this open 

basin include alluvial fans, large submarine landslides, 

and turbidity flows (Southworth et al. 2001). Deposits of 

sand, silt, and mud covered older sediments in 

nearshore, deltaic, barrier island, and tidal flat areas 

along the eastern margin of the North American 

continent (Schwab 1970; Kauffman and Frey 1979; 

Simpson 1991).

Exposed within Hopewell Furnace National Historic Site 

are the massive quartzite and quartz schist of the 

Chickies Formation (Berg et al. 1980). The erosionresistant quartzite, prominent on the ridges in the 

Hopewell Furnace area, is a late Precambrian to early 

Cambrian (~ 550 million years ago) metasedimentary 

rock, originally deposited in near-shore marine 

environments as quartz-rich sandstones (Inners and 

Fergusson 1996; Brown 2002; Topinka 2005). Regionally, 

units such as the Harpers and Antietam formations also 

formed in this depositional environment (Berg et al. 

1980).

Approximately 500 million years ago, the ocean basin 

deepened and the shoreline transgressed onto the 

continental margin, forming the depositional setting for 

chemical sediments (Bechtel et al. 2005). A carbonate 

platform, thickening to the east, was the depositional 

setting for huge masses of carbonate, sandstone, and 

shale rocks that persisted during the Cambrian 

throughout the Ordovician Period (545 to 480 million 

years ago) (Means 1995). The ocean basin deepened, and 

carbonate units precipitated in this depositional 

environment (Means 1995; Bechtel et al. 2005). 

Carbonates (perhaps dolomite of the Vintage Formation) 

may be exposed in the lowest-lying stretches of French 

Creek at Hopewell Furnace (National Park Service 

2009). Regionally, other Cambrian carbonate units 

include the Ledger, Kinzers, Elbrook, Millback, and 

Richland formations (Berg et al. 1980). Limestone 

quarried from these units were incorporated into many 

local buildings and structures, including the furnace at 

Hopewell.

Cambrian to Ordovician units within the regional map 

area of Hopewell Furnace, such as the Conestoga 

Formation, record the transition from the carbonate 

platform to the more nearshore terrestrial deposition 

associated with initial uplift during the Taconic orogeny. 

Taconic Orogeny

Following approximately 50 million years of tectonic 

quiescence and sedimentation, orogenic activity along 

the eastern margin of the North American continent 

began again as a volcanic arc collided with the 

continental mass approximately 440 to 420 million years 
22 NPS Geologic Resources Division 

ago (Means 1995; Bechtel et al. 2005). During the 

Taconic orogeny, compressional tectonic forces closed

the Iapetus Ocean, created volcanic arcs, thrust oceanic 

crust and the volcanic arc from the Iapetus basin onto 

the eastern edge of the North American continent, and 

uplifted the continental crust. The intense heat and 

pressure accompanying deep burial and compressional 

tectonic forces caused metamorphism of igneous and 

nearshore sediments into metabasalts, quartzites and 

phyllites. 

The crust bowed downward west of the rising mountains 

in response to the overriding tectonic plate thrusting 

westward onto the continental margin of North America, 

creating a deep foreland basin that filled with mud and 

sand eroded from the highlands to the east (fig. 12C) 

(Harris et al. 1997). This so-called Appalachian basin, 

centered on what is now West Virginia, collected vast 

amounts of sediments throughout the Paleozoic Era

(fig. 11). 

Acadian Orogeny

The Acadian orogeny (~360 million years ago) continued 

the mountain building of the Taconic orogeny north of 

the Hopewell Furnace area as the African continent 

moved toward North America (Harris et al. 1997). The 

Acadian event involved collision of land masses (North 

American, Europe, and Avalonia [now parts of western 

Europe, eastern North America]), mountain building, 

and regional metamorphism similar to the preceding 

Taconic orogeny (Means 1995; Barnes and Sevon 2002). 

The Acadian mountains formed east of Pennsylvania 

during this event (Barnes and Sevon 2002). Tectonic

quiescence following the Acadian orogeny led to vast 

regional deposition of sediments shed from the eroding 

highlands into the Appalachian basin throughout the 

Mississippian and Pennsylvanian periods (fig. 12C) 

(Barnes and Sevon 2002).

Alleghany Orogeny

During the Late Paleozoic (fig. 11), the proto-Atlantic 

Ocean closed as the North American continent collided 

with the African continent. This formed a supercontinent named Pangaea, and, as a result, formed the 

present-day Appalachian Mountains. The Alleghany

orogeny (~325 to 265 million years ago) was the last 

major mountain-building event to affect the 

Appalachians (fig. 12D) (Means 1995).

During the Alleghany orogeny, a massive block of rocks 

of the Great Valley, Blue Ridge, and Piedmont provinces 

slid along the North Mountain fault as the Blue 

Ridge−Piedmont thrust sheet. The thrust sheet shoved 

westward onto younger rocks of the Valley and Ridge. 

The amount of crustal shortening was very large;

estimates of 20 to 50 % shortening would amount to 125

to 350 km (80 to 220 mi) (Harris et al. 1997).

An estimate of the highest paleoelevation of the 

Alleghany-era Appalachian Mountains is approximately

6,100 m (20,000 ft), making them analogous to the 

modern-day Himalaya Range in Asia. Since their uplift, 

erosion beveled these mountains to elevations less than 

730 m (2,400 ft) above sea level west of Hopewell 

Furnace National Historic Site (Means 1995). Erosion 

exposed the early Paleozoic formations, including the 

quartzites and carbonates, following the Alleghany

orogeny (Bechtel et al. 2005).

Mesozoic Extension (251 to 65.5 million years ago)

During the late Triassic Period, approximately 230 to 200

million years ago, extensional tectonic forces pulled 

apart the supercontinent Pangaea, creating the Atlantic 

Ocean. Along the eastern margin of the North American 

continent, many block-fault basins developed,

accompanied by volcanism (figs. 12E and 13) (Harris et 

al. 1997; Southworth et al. 2001). The uplifted Paleozoic 

units, including the quartzite and carbonate rocks, in the 

Hopewell Furnace area sank in the half-graben 

Gettysburg-Newark Rift Basin formed by reactivated 

Paleozoic thrust faults (Schlische and Olsen 1988; 

Bechtel et al. 2005).

Forces of gravity, wind, and running water eroded and 

transported thick deposits of unconsolidated gravel, 

sand, and silt from the Alleghanian Mountains into rift 

basins such as the Gettysburg-Newark Basin (see figs. 

12E and 3). Throughout the basin, Triassic sandstone 

and shale red beds rest unconformably on the Cambrianage units (Bechtel et al. 2005). The sandstone and 

conglomerate of the Stockton Formation and the 

sandstone, siltstone, and mudstone of the Hammer 

Creek Formation formed in this depositional 

environment in the area of Hopewell Furnace (Inners 

and Fergusson 1996; Brown 2002). The rapid lithologic 

changes within the Triassic rocks record shifting 

depositional regimes from near-shore, fluvial, lacustrine, 

and alluvial fan (Sloto and McManus 1996).

Regional volcanic activity accompanied the rift basin 

formation throughout the Mesozoic. During the Jurassic, 

diabase magma intruded the rift basin sediments. Magma 

that did not reach the surface solidified approximately 

185 to 200 million years ago as diabase dikes, which are 

now exposed by erosion in the Hopewell Furnace area 

(Inners and Fergusson 1996; Brown 2002; Topinka 2005). 

Magma came into contact with the existing

native/country rock, causing changes in its mineralogy 

(W. Kochanov, written communication, 2010). This 

igneous activity formed magnetite (Fe3+

2Fe2+O4) ore 

bodies that became the source of the iron produced at 

Hopewell Furnace National Historic Site (Inners and 

Fergusson 1996).

At nearby Millers Point, the exposure of diabase on the 

edge of the escarpment overlooking the Schuylkill River 

is part of the Morgantown Pluton, a bowl-shaped body 

of igneous intrusive rock exposed on the eastern and 

northern edges of French Creek State Park (Inners and 

Fergusson 1996). The pluton occurs at a depth of about 

1.6 km (1 mi) near Hopewell Lake. A normal fault, along 

which rocks to the south are downdropped relative to 

the rocks to the north, cuts the pluton north of Millers 

Point (Topinka 2005).
HOFU Geologic Resources Inventory 23

As the rift basins filled with sediment, deposition 

continued to spread eastward to form the Atlantic 

Coastal Plain province. Thick layers of Cretaceous units 

(such as the Patapsco Formation) and Tertiary units 

(such as the Pensauken, Bridgeton, and Bryn Mawr 

Formations) east of Hopewell Furnace record this 

environment (fig. 12F) (Duffy and Whittecar 1991; 

Whittecar and Duffy 2000; Berg et al. 1980). An immense 

amount of deposited material is inferred from the nowexposed metamorphic rocks in the Blue Ridge province. 

Many of the rocks exposed at the surface were at least 

20 km (~10 mi) below the surface prior to regional uplift 

and erosion.

Cenozoic Landform Evolution (65.5 million years ago 

until today)

The North American plate continues to move toward the 

west since the breakup of Pangaea and the uplift of the 

Appalachian Mountains. The isostatic adjustments that 

uplifted the continent after the Alleghany orogeny 

continued at a slower rate throughout the Cenozoic Era 

(Harris et al. 1997). Over these millions of years, 

weathering and erosion have beveled the highlands, 

muting the topography, and removing soluble, less 

resistant rocks such as carbonates. Quartzites, being 

more resistant to erosion, stand out as ridges and high 

ground such as Mt. Pleasure. Other rocks weathered to 

produce thick layers of clay-rich saprolite (Barnes and 

Sevon 2002).

Following the early stages of modern drainage 

development in the late Mesozoic and early Cenozoic, 

rivers such as French Creek (that were initially short) 

grew longer through the process of headward erosion. 

Headward erosion generally involves a stream extending 

at its source, but can also include stream piracy in which 

the head of one stream intersects the head of another 

and captures a part of the other’s drainage (Barnes and 

Sevon 2002). 

The masses of continent-scale ice sheets from the 

Pleistocene Ice Ages (most recent advance was about 

19,000 years ago) never reached the Hopewell Furnace 

area in southeastern Pennsylvania. The southern 

terminus was at an elevation of 365 to 610 m (1,200 to 

2,000 ft) in northern Pennsylvania. In the northern part 

of Pennsylvania, glaciers carved upland surfaces into 

rounded ridges and left behind sand- and gravel-filled 

valleys (Davies 2005). However, the colder climates of 

the ice ages played a role in the formation of the 

landscape at the national historic site. The periglacial 

conditions that existed in close proximity to the ice 

sheets intensified weathering and other erosional 

processes such as frost wedging and congelifluction in

which a relatively thin layer of soil and earth thawed and 

moved (slid) during the summer months above a 

permafrost layer (Harris et al. 1997; Sevon and Fleeger 

1999). Talus deposits containing large boulders of 

Chickies quartzite flanking the slopes of Mount Pleasure 

at Hopewell Furnace National Historic Site record the 

periglacial accelerated physical weathering processes 

during the Ice Age (Inners and Fergusson 1996). 

Landforms and gravel deposits such as the Trenton 

Gravel (found east of Hopewell Furnace) formed when a 

wetter climate, sparse vegetation, and frozen ground 

caused increased precipitation to run into the ancestral 

river channels, enhancing downcutting and erosion by 

waterways and causing subsequent increases in 

downstream deposition (Means 1995; Zen 1997a, 1997b).

Erosion throughout the Quaternary Period continues to 

shape the present landscape, with the Schuylkill River 

and its tributaries eroding through thick piles of 

sediments, lowering hill slopes, and depositing alluvial 

terraces along the rivers. Mass wasting processes 

supplement stream erosion, beveling the undulating 

topography. Streams redistribute sediments in riparian 

zones along waterways and intermittently transport them 

toward the Atlantic Ocean to become part of the Atlantic 

Coastal Plain. Anthropogenic land disturbance activities 

such as agriculture, industrialization, deforestation, 

quarrying, and widespread urban development 

exacerbate natural erosion throughout the area.
24 NPS Geologic Resources Division 

Figure 11. Geologic time scale. Included are major life history and tectonic events occurring on the North American continent. Red lines 

indicate major unconformities between eras. Isotopic ages shown are in millions of years (Ma). Compass directions in parentheses indicate 

the regional location of individual geologic events. Adapted from the U.S. Geological Survey, http://pubs.usgs.gov/fs/2007/3015/ with 

additional information from the International Commission on Stratigraphy. http://www.stratigraphy.org/view.php?id=25.
HOFU Geologic Resources Inventory 25

Figure 12. Evolution of the landscape in southern Pennsylvania. Tectonic changes are shown from the Precambrian through the present. Ma = 

Millions of years ago. Graphic by Trista L. Thornberry-Ehrlich (Colorado State University) after Means (1995) and Fedorko et al. (2004). Note: 

graphic is not to scale.
26 NPS Geologic Resources Division 

Figure 13. Triassic extension of the Newark Basin. Graphic by Trista L. Thornberry-Ehrlich (Colorado State University). Note: graphic is not to 

scale.
HOFU Geologic Resources Inventory 27

Glossary

This glossary contains brief definitions of technical geologic terms used in this report. Not all 

geologic terms used are referenced. For more detailed definitions or to find terms not listed

here please visit: http://geomaps.wr.usgs.gov/parks/misc/glossarya.html. Definitions are 

based on those in the American Geological Institute Glossary of Geology (fifth edition; 2005).

absolute age. The geologic age of a fossil, rock, feature, 

or event in years; commonly refers to radiometrically 

determined ages.

alluvial fan. A fan-shaped deposit of sediment that 

accumulates where a hydraulically confined stream 

flows to a hydraulically unconfined area. Commonly 

out of a mountainous area into an area such as a valley 

or plain.

alluvium. Stream-deposited sediment.

anticline. A convex-upward (“A” shaped) fold. Older 

rocks are found in the center.

anticlinorium. A large, regional feature with an overall 

shape of an anticline. Composed of many smaller 

folds.

aquifer. A rock or sedimentary unit that is sufficiently 

porous that it has a capacity to hold water, sufficiently 

permeable to allow water to move through it, and 

currently saturated to some level.

basement. The undifferentiated rocks, commonly 

igneous and metamorphic, that underlie rocks 

exposed at the surface.

basin (structural). A doubly plunging syncline in which 

rocks dip inward from all sides.

basin (sedimentary). Any depression, from continental to 

local scales, into which sediments are deposited.

batholith. A massive, discordant pluton, larger than 100 

km2 (40 mi2), and often formed from multiple 

intrusions of magma.

bedding. Depositional layering or stratification of 

sediments.

block (fault). A crustal unit bounded by faults, either 

completely or in part.

calcareous. Describes rock or sediment that contains the 

mineral calcium carbonate (CaCO3).

carbonate. A mineral that has CO3

-2 as its essential 

component (e.g., calcite and aragonite).

carbonate rock. A rock consisting chiefly of carbonate 

minerals (e.g., limestone, dolomite, or carbonatite).

cementation. Chemical precipitation of material into 

pores between grains that bind the grains into rock.

chemical sediment. A sediment precipitated directly from 

solution (also called nonclastic).

chemical weathering. Chemical breakdown of minerals 

at Earth’s surface via reaction with water, air, or 

dissolved substances; commonly results in a change in 

chemical composition more stable in the current 

environment.

clast. An individual grain or rock fragment in a 

sedimentary rock, produced by the physical 

disintegration of a larger rock mass.

clastic. Describes rock or sediment made of fragments of 

pre-existing rocks (clasts).

clay. Can be used to refer to clay minerals or as a 

sedimentary fragment size classification (less than 

1/256 mm [0.00015 in]).

claystone. Lithified clay having the texture and 

composition of shale but lacking shale’s fine layering 

and fissility (characteristic splitting into thin layers).

concordant. Strata with contacts parallel to the 

orientation of adjacent strata.

conglomerate. A coarse-grained, generally unsorted, 

sedimentary rock consisting of cemented, rounded 

clasts larger than 2 mm (0.08 in).

continental crust. Crustal rocks rich in silica and alumina 

that underlie the continents; ranging in thickness from 

35 km (22 mi) to 60 km (37 mi) under mountain ranges.

convergent boundary. A plate boundary where two 

tectonic plates are colliding.

country rock. The rock surrounding an igneous intrusion 

or pluton. Also, the rock enclosing or traversed by a 

mineral deposit.

craton. The relatively old and geologically stable interior 

of a continent (also see “continental shield”).

creep. The slow, imperceptible downslope movement of 

mineral, rock, and soil particles under gravity.

cross-bedding. Uniform to highly varied sets of inclined 

sedimentary beds deposited by wind or water that 

indicate flow conditions such as water flow direction 

and depth.

cross section. A graphical interpretation of geology, 

structure, and/or stratigraphy in the third (vertical) 

dimension based on mapped and measured geological 

extents and attitudes depicted in a vertically oriented 

plane.

crust. Earth’s outermost compositional shell, 10 to 40 km 

(6 to 25 mi) thick, consisting predominantly of 

relatively low-density silicate minerals (also see 

“oceanic crust” and “continental crust”).

crystalline. Describes a regular, orderly, repeating 

geometric structural arrangement of atoms.

deformation. A general term for the process of faulting, 

folding, and shearing of rocks as a result of various 

Earth forces such as compression (pushing together) 

and extension (pulling apart).

delta. A sediment wedge deposited where a stream flows 

into a lake or sea.

dike. A narrow igneous intrusion that cuts across 

bedding planes or other geologic structures.

dip. The angle between a bed or other geologic surface 

and horizontal.

divergent boundary. An active boundary where tectonic 

plates are moving apart (e.g., a spreading ridge or 

continental rift zone).

dolomite. A carbonate sedimentary rock of which more 

than 50% by weight or by areal percentages under the 
28 NPS Geologic Resources Division 

microscope consists of the mineral dolomite (calciummagnesium carbonate).

drainage basin. The total area from which a stream 

system receives or drains precipitation runoff.

escarpment. A steep cliff or topographic step resulting 

from vertical displacement on a fault or by mass 

movement. Also called a “scarp.”

extrusive. Describes igneous material that has erupted 

onto Earth’s surface.

facies (metamorphic). The pressure and temperature 

conditions that result in a particular, distinctive suite 

of metamorphic minerals.

facies (sedimentary). The depositional or environmental 

conditions reflected in the sedimentary structures, 

textures, mineralogy, fossils, etc. of a sedimentary 

rock.

fanglomerate. A sedimentary rock of heterogeneous 

materials that were originally deposited in an alluvial 

fan and have since been cemented into solid rock.

fault. A break in rock along which relative movement has 

occurred between the two sides.

footwall. The mass of rock beneath a fault surface (also 

see “hanging wall”).

formation. Fundamental rock-stratigraphic unit that is 

mappable, lithologically distinct from adjoining strata, 

and has definable upper and lower contacts.

fracture. Irregular breakage of a mineral; also any break 

in a rock (e.g., crack, joint, or fault).

frost wedging. The breakup of rock due to the 

expansion of water freezing in fractures.

graben. A down-dropped structural block bounded by 

steeply dipping, normal faults (also see “horst”).

hanging wall. The mass of rock above a fault surface 

(also see “footwall”).

horst. Areas of relative “up” between grabens, 

representing the geologic surface left behind as 

grabens drop. The best example is the Basin-andRange province of Nevada. The basins are grabens 

and the ranges are weathered horsts. Grabens become 

a locus for sedimentary deposition (also see “graben”). 

igneous. Refers to a rock or mineral that originated from 

molten material; one of the three main classes of 

rocks—igneous, metamorphic, and sedimentary.

intrusion. A body of igneous rock that invades (pushes 

into) older rock. The invading rock may be a plastic 

solid or magma.

island arc. A line or arc of volcanic islands formed over 

and parallel to a subduction zone.

isostacy. The condition of equilibrium, comparable to 

floating, of the units of the lithosphere above the 

asthenosphere. Crustal loading (commonly by large ice 

sheets) leads to isostatic depression or downwarping; 

removal of the load leads to isostatic uplift or 

upwarping.

joint. A break in rock without relative movement of 

rocks on either side of the fracture surface.

karst topography. Topography characterized by 

abundant sinkholes and caverns formed by the 

dissolution of calcareous rocks.

lacustrine. Pertaining to, produced by, or inhabiting a 

lake or lakes.

lamination. Very thin, parallel layers.

landslide. Any process or landform resulting from rapid, 

gravity-driven mass movement.

lava. Still-molten or solidified magma that has been 

extruded onto Earth’s surface though a volcano or 

fissure.

limestone. A sedimentary rock consisting chiefly of 

calcium carbonate, primarily in the form of the mineral 

calcite.

lineament. Any relatively straight surface feature that can 

be identified via observation, mapping, or remote 

sensing, often reflects crustal structure.

lithify. To change to stone or to petrify; especially to 

consolidate from a loose sediment to a solid rock 

through compaction and cementation. 

lithology. The physical description or classification of a 

rock or rock unit based on characters such as its color, 

mineral composition, and grain size.

mafic. Describes dark-colored rock, magma, or minerals 

rich in magnesium and iron. Compare to “felsic.”

magma. Molten rock beneath Earth’s surface capable of 

intrusion and extrusion. 

mantle. The zone of Earth’s interior between the crust 

and core.

mass wasting. A general term for the downslope 

movement of soil and rock material under the direct 

influence of gravity.

mechanical weathering. The physical breakup of rocks 

without change in composition. Synonymous with 

“physical weathering.”

metamorphism. Literally, a change in form. 

Metamorphism occurs in rocks through mineral 

alteration, formation, and/or recrystallization from 

increased heat and/or pressure.

mineral. A naturally occurring, inorganic crystalline solid 

with a definite chemical composition or compositional 

range.

nonconformity. An erosional surface preserved in strata 

in which crystalline igneous or metamorphic rocks 

underlie sedimentary rocks.

normal fault. A dip-slip fault in which the hanging wall 

moves down relative to the footwall.

obduction. The process by which the crust is thickened 

by thrust faulting at a convergent margin.

oceanic crust. Earth’s crust formed at spreading ridges 

that underlies the ocean basins. Oceanic crust is 6 to 7 

km (3 to 4 miles) thick and generally of basaltic 

composition.

orogeny. A mountain-building event.

outcrop. Any part of a rock mass or formation that is 

exposed or “crops out” at Earth’s surface.

parent material. Geologic material from which soils 

form.

passive margin. A margin where no plate-scale tectonism 

is taking place; plates are not converging, diverging, or 

sliding past one another. An example is the east coast 

of North America. (also see “active margin”).

permeability. A measure of the relative ease with which 

fluids move through the pore spaces of rocks or 

sediments.

phyllite. A metamorphosed rock, intermediate in grade 

between slate and mica schist, with minute crystals of 

graphite, sericite, or chlorite that impart a silky sheen 

to the surfaces (“schistosity”).
HOFU Geologic Resources Inventory 29

plateau. A broad, flat-topped topographic high 

(terrestrial or marine) of great extent and elevation 

above the surrounding plains, canyons, or valleys.

pluton (plutonic). A body of intrusive igneous rock that 

crystallized at some depth beneath Earth’s surface.

porosity. The proportion of void space (e.g., pores or 

voids) in a volume of rock or sediment deposit.

progradation. The seaward building of land area due to 

sedimentary deposition.

radioactivity. The spontaneous decay or breakdown of 

unstable atomic nuclei.

radiometric age. An age expressed in years and 

calculated from the quantitative determination of 

radioactive elements and their decay products. 

recharge. Infiltration processes that replenish 

groundwater.

regression. A long-term seaward retreat of the shoreline 

or relative fall of sea level.

relative dating. Determining the chronological 

placement of rocks, events, or fossils with respect to 

the geologic time scale and without reference to their 

numerical age.

reverse fault. A contractional high-angle (greater than 

45°) dip-slip fault in which the hanging wall moves up 

relative to the footwall (also see “thrust fault”).

rift. A region of crust where extension results in 

formation of many related normal faults, often 

associated with volcanic activity.

rift valley. A depression formed by grabens along the 

crest of an oceanic spreading ridge or in a continental 

rift zone.

sand. A clastic particle smaller than a granule and larger 

than a silt grain, having a diameter in the range of 1/16 

mm (0.0025 in) to 2 mm (0.08 in).

sandstone. Clastic sedimentary rock of predominantly 

sand-sized grains.

scarp. A steep cliff or topographic step resulting from 

displacement on a fault, or by mass movement, or 

erosion. Also called an “escarpment.”

sediment. An eroded and deposited, unconsolidated 

accumulation of rock and mineral fragments.

sedimentary rock. A consolidated and lithified rock 

consisting of clastic and/or chemical sediment(s). One 

of the three main classes of rocks—igneous, 

metamorphic, and sedimentary.

shale. A clastic sedimentary rock made of clay-sized 

particles that exhibit parallel splitting properties.

silt. Clastic sedimentary material intermediate in size 

between fine-grained sand and coarse clay (1/256 to 

1/16 mm [0.00015 to 0.002 in]).

siltstone. A variably lithified sedimentary rock composed 

of silt-sized grains.

slope. The inclined surface of any geomorphic feature or 

measurement thereof. Synonymous with “gradient.”

slump. A generally large, coherent mass movement with a 

concave-up failure surface and subsequent backward 

rotation relative to the slope.

soil. Surface accumulation of weathered rock and 

organic matter capable of supporting plant growth and 

often overlying the parent material from which it 

formed.

spring. A site where water issues from the surface due to 

the intersection of the water table with the ground 

surface.

strata. Tabular or sheet-like masses or distinct layers of 

rock.

stratigraphy. The geologic study of the origin, 

occurrence, distribution, classification, correlation, 

and age of rock layers, especially sedimentary rocks.

stream. Any body of water moving under gravity flow in 

a clearly confined channel.

stream channel. A long, narrow depression shaped by the 

concentrated flow of a stream and covered 

continuously or periodically by water.

stream terrace. Step-like benches surrounding the 

present floodplain of a stream due to dissection of 

previous flood plain(s), stream bed(s), and/or valley 

floor(s).

strike. The compass direction of the line of intersection 

of an inclined surface with a horizontal plane.

strike-slip fault. A fault with measurable offset where the 

relative movement is parallel to the strike of the fault. 

Said to be “sinistral” (left-lateral) if relative motion of 

the block opposite the observer appears to be to the 

left. “Dextral” (right-lateral) describes relative motion 

to the right.

structure. The attitude and relative positions of the rock 

masses of an area resulting from such processes as 

faulting, folding, and igneous intrusions.

subduction zone. A convergent plate boundary where 

oceanic lithosphere descends beneath a continental or 

oceanic plate and is carried down into the mantle.

subsidence. The gradual sinking or depression of part of 

Earth’s surface.

syncline. A downward curving (concave up) fold with 

layers that dip inward; the core of the syncline 

contains the stratigraphically-younger rocks.

synclinorium. A composite synclinal structure of regional 

extent composed of lesser folds.

tectonic. Relating to large-scale movement and 

deformation of Earth’s crust.

terrace. A relatively level bench or steplike surface 

breaking the continuity of a slope (see “marine 

terrace” and “stream terrace”).

terrane. A large region or group of rocks with similar 

geology, age, or structural style.

terrestrial. Relating to land, Earth, or its inhabitants.

thrust fault. A contractional dip-slip fault with a 

shallowly dipping fault surface (less than 45°) where 

the hanging wall moves up and over relative to the 

footwall.

topography. The general morphology of Earth’s surface, 

including relief and locations of natural and 

anthropogenic features.

trace (fault). The exposed intersection of a fault with 

Earth’s surface.

trace fossil. Tracks, trails, burrows, coprolites (dung), 

etc., that preserve evidence of organisms’ life activities, 

rather than the organisms themselves.

transgression. Landward migration of the sea as a result 

of a relative rise in sea level.

trend. The direction or azimuth of elongation of a linear 

geologic feature.
30 NPS Geologic Resources Division 

type locality. The geographic location where a 

stratigraphic unit (or fossil) is well displayed, formally 

defined, and derives its name. The place of original 

description.

unconformity. An erosional or non-depositional surface 

bounded on one or both sides by sedimentary strata 

that marks a period of missing time.

uplift. A structurally high area in the crust, produced by 

movement that raises the rocks.

volcanic. Describes anything related to volcanoes. Can 

refer to igneous rock crystallized at or near Earth’s 

surface (e.g., lava).

water table. The upper surface of the saturated zone; the 

zone of rock in an aquifer saturated with water.

weathering. The physical, chemical, and biological 

processes by which rock is broken down.
HOFU Geologic Resources Inventory 31

Literature Cited

This section lists references cited in this report. A more complete geologic bibliography is 

available from the National Park Service Geologic Resources Division.

Anonymous. 2002. Pennsyvlanian Coal Mine Drainage 

Projects. Coal International 250 (6):254–260.

Barnes, J. H. and W. D. Sevon. 2002. The Geological 

Story of Pennsylvania. Educational Series 4. 

Department of Conservation and Natural Resources, 

Bureau of Topographic and Geologic Survey, 

Harrisburg, Pennsylvania, USA.

(http://www.dcnr.state.pa.us/topogeo/education/es4.p

df) Accessed 20 May 2010. 

Bascom, F. and G. W. Stose. 1938. Geology and Mineral 

Resources of the Honeybrook and Phoenixville 

Quadrangles, Pennsylvania. Bulletin 891. U.S. 

Geological Survey, Reston, Virginia, USA.

Bechtel, T. D., J. L. Hojdila, S. H. Baughman II, T.

DeMayo, and E. Doheny. 2005. Relost and Refound: 

Detection of a Paleontologically, Historically, 

Cinematically(?), and Environmentally Important 

Solution Feature in the Carbonate Belt of Southeastern 

Pennsylvania. Leading Edge Tulsa, Oklahoma K 24 

(5):537–540. 

Berg, T. M., A. D. Glover, S. I. Root, W. E. Edmunds, D.

M. Hoskins, W. D. Sevon, A. R. Geyer, D. B. 

MacLachlan, and A. A. Socolow. 1980. Geologic Map 

of Pennsylvania (scale 1:250,000). 4th series, PA DCNR 

Map 1. Bureau of Topographic and Geologic Survey, 

Harrisburg, Pennsylvania, USA.

Berg, T. M. and C. M. Dodge (compilers). 1981. Atlas of 

Preliminary Geologic Quadrangle Maps of 

Pennsylvania. Map 61, 4th Series. Bureau of 

Topographic and Geologic Survey, Harrisburg, 

Pennsylvania, USA. 

(http://www.dcnr.state.pa.us/topogeo/map61/61intro.

aspx) Accessed 5 February 2009.

Bining, A. C. 1938. Pennsylvania Iron Manufacture in the 

Eighteenth Century. Publications of the Pennsylvania 

Historical Commission, Harrisburg, Pennsylvania, 

USA.

Brown, C. D. 2002. Notable Geologic Features of the 

Philadelphia Region. 

(http://www.philageo.org/features.html). Accessed 5 

January 2009.

Hopewell Furnace National Historic Site. 1993. LongRange Interpretive Plan: Hopewell Furnace National 

Historic Site. Document 35. Hopewell Furnace 

National Historic Site, Elverson, Pennsylvania, USA.

Davies, W. E. 2005. Physiography. 

(http://www.cagenweb.com/quarries/articles_and_boo

ks/min_res_appalachian_region/physiography.html). 

Accessed 4 November 2005.

Demer, J. 2003. Historic Furnishings Report: Cast House, 

Hopewell Furnace National Historic Site, Elverson, 

Pennsylvania. Harpers Ferry Center, National Park 

Service, Harpers Ferry, West Virginia, USA. 

(http://www.nps.gov/history/history/park_histories/in

dex.htm#h) Accessed 20 May 2010.

Duffy, D. F. and G. R. Whittecar. 1991. Geomorphic 

Development of Segmented Alluvial Fans in the 

Shenandoah Valley, Stuarts Draft, Virginia. Geological 

Society of America Abstracts with Programs 23 (1):24.

Emrich, G. H. 1984. Groundwater. In Journal – Water 

Pollution Control Federation 56 (6):707–708.

Fedorko, N., W. C. Grady, C. F. Eble, and B. C. Cecil. 

2004. Stop 1: Upper Conemaugh and Lower 

Monongahela Group Strata on the North Side of the 

Morgantown Mall Complex on Interstate 79 at Exit 

152, Morgantown, W. Va. Southworth, S. and W. 

Burton, editors. Geology of the National Capital 

Region: Field Trip Guidebook. Circular 1264. U.S. 

Geological Survey, Reston, Virginia, USA.

(http://pubs.er.usgs.gov/usgspubs/cir/cir1264) 

Accessed 20 May 2010.

Fergusson, W. B. 1974. French Creek State Park: Story of 

the Rocks. Park Guide 6. Bureau of Topographic and 

Geologic Survey, Harrisburg, Pennsylvania, USA.

Glaser, L. 2005. Hopewell Furnace National Historic Site 

Administrative History. Northeast Regional Office, 

National Park Service, Philadelphia, Pennsylvania, 

USA.

(http://www.nps.gov/history/history/park_histories/in

dex.htm#h). Accessed 20 May 2010.

Harris, A. G., E. Tuttle, and S. D. Tuttle. 1997. Geology of 

National Parks. Kendall/Hunt Publishing Company, 

Dubuque, Iowa, USA.

Inners, J. D. and W. B. Fergusson. 1996. French Creek 

State Park: Piedmont Rocks and Hopewell Furnace, 

Pennsylvania Trail of Geology. Park Guide 6. Bureau 

of Topographic and Geologic Survey, Harrisburg, 

Pennsylvania, USA. 

(http://www.dcnr.state.pa.us/topogeo/parkguides/trail

.aspx). Accessed 20 May 2010.

Kauffman, M. E and E. P. Frey. 1979. Antietam 

Sandstone Ridges: Exhumed Barrier Islands or FaultBounded Blocks? Geological Society of America 

Abstracts with Programs 11 (1):18.
32 NPS Geologic Resources Division 

Kenworthy, J. P., C. C. Visaggi, and V. L. Santucci. 2006. 

Paleontological Resource Inventory and Monitoring, 

Mid-Atlantic Network. TIC #D-800, National Park 

Service. 

Layton, E., D. Lehmann, W. Mader, E. Teeters, and D.

McKee. 2006. Characterization of an Appalachian 

Colluvial Deposit and its Impact upon Groundwater 

Flow, Centre County, Pennsylvania. Geological 

Society of America Abstracts with Programs 38 (2):87.

Lewis, W. D. and W. Hugins. 1983. Hopewell Furnace: A 

Guide to Hopewell Furnace National Historic Site, 

Pennsylvania. Handbook 124:6–21. National Park 

Service.

(http://www.nps.gov/history/history/park_histories/in

dex.htm#h) Accessed 20 May 2010.

Means, J. 1995. Maryland's Catoctin Mountain Parks: An 

Interpretive Guide to Catoctin Mountain Park and 

Cunningham Falls State Park. McDonald & 

Woodward Publishing Company, Blacksburg, Virginia, 

USA.

Miles, C. E. and T. G. Whitfield, compilers. 2001. 

Bedrock Geology of Pennsylvania (scale 1:250,000). 

Digital dataset extracted from Geologic Map of 

Pennsylvania. 4th ser., PA DCNR Map 1. Bureau of 

Topographic and Geologic Survey, Harrisburg, 

Pennsylvania, USA.

National Park Service (NPS). 1997. Hopewell Furnace: A 

Pennsylvania Iron-Making Plantation. 

(http://www.nps.gov/history/nr/twhp/wwwlps/lessons

/97hopewell/97hopewell.htm). Accessed 5 January 

2009.

National Park Service (NPS). 1998. Baseline Water 

Quality Data Inventory and Analysis: Hopewell 

Furnace National Historic Site. Technical Report 

NPS/NRWRD/NRTR-98/191 (TIC # D-73). NPS 

Water Resources Division and Servicewide Inventory 

and Monitoring Program, Fort Collins, Colorado, 

USA. (http://nature.nps.gov/water/horizon.cfm). 

Accessed 20 May 2010.

National Park Service (NPS). 2009. Natural Resources. 

(http://www.nps.gov/archive/hofu/RMnatural.html). 

Accessed 5 January 2009.

Nickelsen, R. P. 1983. Aspects of Alleghanian 

Deformation. Pages 29–39 in Nickelsen, R. P. and E. 

Cotter, editors. Silurian Depositional History and 

Alleghanian Deformation in the Pennsylvania Valley 

and Ridge. Guidebook for the Annual Field 

Conference of Pennsylvania Geologists 48. 

Nikitina, D. L. 2003. Geology of Western Pennsylvania in 

the Classroom and in the Field. Geological Society of 

America Abstracts with Programs35 (6):275. 

O’Neill, B. J. 1976. Our Mineral Heritage: Hopewell 

Village. Pennsylvania Geology 7 (3):2–5.

Pennsylvania Geological Survey. 2000. Map 13, 

Physiographic Provinces of Pennsylvania. 

Pennsylvania Department of Conservation and 

Natural Resources. 

(http://www.dcnr.state.pa.us/topogeo/map13/map13.a

spx). Accessed 26 January 2006.

Podniesinski, G. S., S. J. Perles, L. A. Sneddon, and B.

Millinor. 2005. Vegetation Classification and Mapping

of the Hopewell Furnace National Historic Site. 

Technical Report NPS/NER/NRTR—2005/012. 

National Park Service, Philadelphia, Pennsylvania, 

USA.

(http://biology.usgs.gov/npsveg/hofu/index.html). 

Accessed 20 May 2010.

Robinson & Associates, Inc. 2004. Hopewell Furnace 

National Historic Site Historic Resource Study-Final. 

(http://www.nps.gov/history/history/online_books/ho

fu/hrs.pdf). Accessed 4 February 2009.

Root, S. I. 1989. Basement Control of Structure in the 

Gettysburg Rift Basin, Pennsylvania and Maryland. 

Tectonophysics 166 (4):281–292. 

Santucci, V. L., J. P. Kenworthy, and A. L. Mims. 2009. 

Monitoring in situ paleontological resources. Pages 

189-204 in Young, R. and L. Norby, editors. Geological 

monitoring. Geological Society of America, Boulder, 

Colorado, USA.

Schlische, R. W. and P. E. Olsen. 1988. A Model for the 

Structural Evolution of the Newark Basin. Geological 

Society of America Abstracts with Programs 20 (1):68.

Schuller, R. M., W. W. Beck, Jr., and D. R. Price. 1982. 

Case Study of Contaminant Reversal and 

Groundwater Restoration in a Fractured Bedrock. 

Pages 94–96 in Bernard, H., B. Bixler, D. Lamont, H.

Masters, J. Rollo, D. Sanning, H. Snyder, Jr., and W. K. 

Tusa, compilers. Management of Uncontrolled 

Hazardous Waste Sites. Hazard Master Control 

Research Institute, Silver Spring, Maryland, USA.

Schwab, F. L. 1970. Origin of the Antietam Formation 

(late Precambrian?, lower Cambrian), Central Virginia. 

In Journal of Sedimentary Petrology 40 (1):354–366.

Sevon, W. D. 2000. Physiographic Provinces of 

Pennsylvania (scale 1:2,000,000). Map 13. 4th edition. 

Bureau of Topographic and Geologic Survey, 

Harrisburg, Pennsylvania, USA.

Sevon, W. D. and G. M. Fleeger. 1999. Pennsylvania and 

the Ice Age. Educational Series 6. Department of 

Conservation and Natural Resources, Bureau of 

Topographic and Geologic Survey, Harrisburg, 

Pennsylvania, USA.

Simpson, E. L. 1991. An Exhumed Lower Cambrian 

Tidal-Flat: The Antietam Formation, Central Virginia, 

U.S.A. Pages 123–133 in Smith, D. G., B. A. Zaitlin, G. 

E. Reinson, and R. A. Rahmani, editors. Clastic Tidal 
HOFU Geologic Resources Inventory 33

Sedimentology. Memoir 16, Canadian Society of 

Petroleum Geologists, Calgary, Alberta, Canada.

Sloto, R. A. and B. C. McManus. 1996. Hydrology and 

Ground-Water Quality of Valley Forge National 

Historical Park, Montgomery County, Pennsylvania. 

Water-Resources Investigations WRI 96-4120. U.S. 

Geological Survey, Reston, Virginia, USA.

(http://pubs.er.usgs.gov/usgspubs/wri/wri964120) 

Accessed 20 May 2010.

Smith, L. L. 1931. Magnetite Deposits of French Creek, 

Pennsylvania (scale 1:62,500). Mineral Resources 

Report M14, 4th Series. Bureau of Topographic and 

Geologic Survey, Harrisburg, Pennsylvania, USA.

Southworth, S., D. K. Brezinski, R. C. Orndorff, P. G. 

Chirico, and K. M. Lagueux. 2001. Geology of the 

Chesapeake and Ohio Canal National Historical Park 

and Potomac River Corridor, District of Columbia, 

Maryland, West Virginia, and Virginia. (A - geologic 

map and GIS files [disc 1]; B - geologic report and 

figures [disc 2]). Open-File Report: OF 01-0188. U.S. 

Geological Survey, Reston, Virginia, USA.

(http://pubs.usgs.gov/of/2001/of01-188/). Accessed 20 

May 2010.

Thornberry-Ehrlich, T. E. 2009. Catoctin Mountain Park 

Geologic Resources Inventory Report. Natural 

Resource Report NPS/NRPC/GRD/NRR—2009/120.

(http://www.nature.nps.gov/geology/inventory/gre_pu

blications.cfm#C). Accessed 20 May 2010.

Topinka, L. 2005. America’s Volcanic Past: Pennsylvania. 

U.S. Geological Survey Cascades Volcano 

Observatory, Vancouver, Washington, USA. 

(http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/P

laces/volcanic_past_pennsylvania.html). Accessed 5 

January 2009. 

Tsusue, A. 1964. Mineral Aspects of the Grace Mine 

Magnetite Deposit, Pennsylvania. Mineral Resources 

Report M49, 4th Series. Bureau of Topographic and 

Geologic Survey, Harrisburg, Pennsylvania, USA.

Vaux, G., Jr. 1926. Some Unusual Quartz Pseudomorphs 

From the Hopewell Mine, Warwick Township, 

Chester County, Pennsylvania. Pages 17–19 in

Proceedings of the Academy of Natural Sciences of 

Philadelphia 78.

Whittecar, G. R. and D. F. Duffy. 2000. Geomorphology 

and Stratigraphy of Late Cenozoic Alluvial Fans, 

Augusta County, Virginia, U.S.A. Pages 259–279 in 

Clark, G. M., H. H. Mills, and J. S. Kite, editors.

Regolith in the Central and Southern Appalachians,

Southeastern Geology 39 (3-4).

Yocum, B. A. 2008. The Furnace Group Historic 

Structure Report, Hopewell Furnace National Historic 

Site, Elverson, Pennsylvania. National Park Service 

Historic Architecture Program, Northeast Region, 

Lowell, Massachusetts, USA. 

(http://www.nps.gov/history/history/park_histories/in

dex.htm#h) Accessed 20 May 2010.

Zen, E-an. 1997a. The Seven-Storey River: 

Geomorphology of the Potomac River Channel 

between Blockhouse Point, Maryland, and 

Georgetown, District of Columbia, With Emphasis on 

The Gorge Complex Below Great Falls. Open-File 

Report OF 97-60. U.S. Geological Survey, Reston, 

Virginia, USA.

(http://pubs.er.usgs.gov/usgspubs/ofr/ofr9760) 

Accessed 20 May 2010.

Zen, E-an. 1997b. Channel Geometry and Strath Levels 

of the Potomac River Between Great Falls, Maryland, 

and Hampshire, West Virginia. Open-File Report OF 

97-480. U.S. Geological Survey, Reston, Virginia, USA.

(http://pubs.er.usgs.gov/usgspubs/ofr/ofr97480) 

Accessed 20 May 2010.
34 NPS Geologic Resources Division 

Additional References

This section lists additional references, resources, and web sites that may be of use to 

resource managers. 

Geology of National Park Service Areas

NPS Geologic Resources Division (Lakewood, 

Colorado). http://nature.nps.gov/geology/

NPS Geologic Resources Inventory Publications. 

http://www.nature.nps.gov/geology/inventory/gre_pu

blications.cfm

U.S. Geological Survey Geology of National Parks 

(includes 3D photographs). 

http://3dparks.wr.usgs.gov/

Harris, A. G., E. Tuttle, and S. D. Tuttle. 2003. Geology of 

National Parks. Sixth Edition. Kendall/Hunt 

Publishing Co., Dubuque, Iowa, USA.

Kiver, E. P. and D. V. Harris. 1999. Geology of U.S. 

parklands. John Wiley and Sons, Inc., New York, New 

York, USA.

Lillie, R. J. 2005. Parks and Plates: The geology of our 

national parks, monuments, and seashores. W.W. 

Norton and Co., New York, New York, USA.

NPS Geoscientist-in-the-parks (GIP) internship and 

guest scientist program. 

http://www.nature.nps.gov/geology/gip/index.cfm

Resource Management/Legislation Documents

NPS 2006 Management Policies (Chapter 4; Natural 

Resource Management): 

http://www.nps.gov/policy/mp/policies.html#_Toc157

232681

NPS-75: Natural Resource Inventory and Monitoring 

Guideline:

http://www.nature.nps.gov/nps75/nps75.pdf.

NPS Natural Resource Management Reference Manual 

#77: http://www.nature.nps.gov/Rm77/

Geologic Monitoring Manual

R. Young and L. Norby, editors. Geological 

Monitoring. Geological Society of America, Boulder, 

Colorado. [Website under development]. Contact the 

Geologic Resources Division to obtain a copy.

NPS Technical Information Center (Denver, repository 

for technical (TIC) documents): http://etic.nps.gov/

Geological Survey Websites

Pennsylvania Geological Survey: 

http://www.dcnr.state.pa.us/topogeo/index.aspx

Berg, T. M. and C. M. Dodge, compilers. 1981. Atlas of 

preliminary geologic quadrangle maps of 

Pennsylvania. Map 61, 4th Series. Bureau of 

Topographic and Geologic Survey, Middletown, 

Pennsylvania, USA.

http://www.dcnr.state.pa.us/topogeo/map61/61intro.a

spx.

Smith, L. L. 1931. Magnetite deposits of French Creek, 

Pennsylvania (scale 1:62,500). Mineral Resources 

Report M14, 4th Series. Bureau of Topographic and 

Geologic Survey, Middletown, Pennsylvania, USA.

Tsusue, A. 1964. Mineral aspects of the Grace mine 

magnetite deposit, Pennsylvania. Mineral Resources 

Report M49, 4th Series. Bureau of Topographic and 

Geologic Survey, Middletown, Pennsylvania, USA.

U.S. Geological Survey: http://www.usgs.gov/

Geological Society of America: 

http://www.geosociety.org/

American Geological Institute: http://www.agiweb.org/

Association of American State Geologists: 

http://www.stategeologists.org/

Other Geology/Resource Management Tools

Bates, R. L. and J. A. Jackson, editors. American 

Geological Institute dictionary of geological terms (3rd 

Edition). Bantam Doubleday Dell Publishing Group, 

New York.

U.S. Geological Survey National Geologic Map Database 

(NGMDB): http://ngmdb.usgs.gov/

U.S. Geological Survey Geologic Names Lexicon 

(GEOLEX; geologic unit nomenclature and summary): 

http://ngmdb.usgs.gov/Geolex/geolex_home.html

U.S. Geological Survey Geographic Names Information 

System (GNIS; search for place names and geographic 

features, and plot them on topographic maps or aerial 

photos): http://gnis.usgs.gov/

U.S. Geological Survey GeoPDFs (download searchable 

PDFs of any topographic map in the United States): 

http://store.usgs.gov (click on “Map Locator”).

U.S. Geological Survey Publications Warehouse (many 

USGS publications are available online): 

http://pubs.usgs.gov
HOFU Geologic Resources Inventory 35

Appendix A: Overview of Digital Geologic Data

The following page is an overview of the digital geologic data for Hopewell Furnace 

National Historic Site. For a poster-size PDF of this overview and complete digital data, 

please see the included CD or visit the Geologic Resources Inventory publications web

site (http://www.nature.nps.gov/geology/inventory/gre_publications.cfm).

The Department of the Interior protects and manages the nation’s natural resources and cultural heritage; provides scientific and other 

information about those resources; and honors its special responsibilities to American Indians, Alaska Natives, and affiliated Island 

Communities. 

NPS 376/103722, June 2010 
National Park Service 

U.S. Department of the Interior 

Natural Resource Program Center 

1201 Oakridge Drive, Suite 150 

Fort Collins, CO 80525 

www.nature.nps.gov 

EXPERIENCE YOUR AMERICATM