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CAPE ANN
MASSACHUSETTS
Its Physical and Environmental Geology
Martin E. Ross, Ph.D.
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Copyright 2015
Martin E. Ross
ISBN # 978-0-692-35288-5
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For Maggie and Morgan
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Table of Contents
About the Author............................................................................v
Preface.............................................................................................vi
Part I: Geologic Features and Processes on Cape Ann
Chapter 1. Introduction and Surficial features and processes.........1
Chapter 2. Igneous Rocks and Processes.........................................16
Chapter 3. Plate tectonics.................................................................32
Chapter 4. The Igneous rocks of Cape Ann.....................................37
Chapter 5. The Geologic History of Cape Ann................................47
Chapter 6. The Environmental Geology of Cape Ann.....................54
Part II. Geologic Guides to Selected Localities on Cape Ann
Chapter 7. The Geology of Rafes Chasm, Gloucester.........................82
Chapter 8. The Geology of Stage Fort Park, Gloucester.....................93
Chapter 9. The Geology of Good Harbor Beach Area........................98
Chapter 10. The Geology at the End of Route 128...........................106
Chapter 11. The Geology of Rockport’s Southern Beaches.............114
Chapter 12. The Geology of The Headlands, Rockport....................115
Chapter 13. The Geology of Front and back Beaches, Rockport.....128
Chapter 14. The Geology of Andrews Point, Rockport....................134
Chapter 15. The Geology of Halibut Point State Park......................155
Chapter 16. The Geology of Lanes Cove, Gloucester.......................165
Glossary..............................................................................................169
References..........................................................................................174
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About the Author
Since receiving his doctorate from the University of Idaho in 1978, Dr. Ross has been teaching geology
at Northeastern University in Boston. Ross’s local, ongoing research has been a detailed field and laboratory
investigation of the many intrusive mafic igneous rocks of the Avalon terrane of eastern Massachusetts. In
addition, Ross is currently engaged in a decades-long investigation of the basalt lava flows and related volcanics
of the northwestern United States. Ross also has consulting experience in the area of geologic hazards and land-
use planning of small communities along the Oregon Coast. Dr. Ross has lived on Cape Ann since 1980.
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PREFACE
Cape Ann, a mere hour’s drive or train ride north of Boston, is well-known for its scenic, rocky shoreline
and numerous beautiful beaches. It has a long history of commercial fishing. Less well-known is its quarrying
industry that thrived during much of the 19th century before dying out in the early 20th century. Barbara Erkkila’s
excellent book, “Hammers on Stone” provides a historic account of the granite industry here. What remains
largely unknown to its residents and visitors are the fascinating geologic history of Cape Ann and the geologic
processes that continue to modify it. This book introduces the layman to Cape Ann’s geology as well as
environmental problems resulting from our inattention to geologic processes when making land use decisions.
My intent is to provide in one volume, enough information to allow a non-geologist or beginning geologist to
directly observe and understand geologic features and processes using Cape Ann as the vehicle.
Since the late 19th century geologists have been aware of the geology of Cape Ann with many of us
having conducted detailed research of its rocks and structures. Most of what has been written about the geology
of Cape Ann has been for other geologists with precious little available for public consumption.
This book is divided into two parts: Part I consists of Chapters 1 through 6 and lay the groundwork by
providing the tools that will enable the reader to better understand the remainder of the book. Part II consists
of Chapters 7 through 16 in which the geology of selected localities on Cape Ann are described in detail.
Chapter 1 serves as an introduction to Cape Ann’s geology by describing its major surficial landforms
and resources (streams, ponds, wetlands, groundwater, glacial features, and coastal features) and explaining their
origins. Chapter 2 discusses the nature, origin, and classification of igneous rocks in general since the bedrock
of Cape Ann consists entirely of igneous rocks. Igneous minerals and textures are introduced and there is a
lengthy section on magma processes. Chapter 3 introduces the exciting topic of plate tectonics with a brief
account of its role in forming Cape Ann. Chapter 4 describes the rocks of Cape Ann, laying the groundwork
for later chapters. Chapter 5 delves into the geologic history of the cape, including the role of plate tectonics
in its formation.
In a departure from the first five chapters, Chapter 6 is devoted entirely to the environmental geology
of Cape Ann. It is intended to illustrate the many problems, both for the natural environment and for humans,
that result from land use practices that too often pay little attention to geologic limitations.
Part II is intended to be a field guide to ten localities with maps and illustrations that allow the reader
to more readily find and observe the geologic features described. With this information in hand, I hope that
readers will visit these sites so that they can more fully appreciate and understand the rocks of Cape Ann and
the geologic processes responsible for them.
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