Geological Survey Bulletin 1309 The Geologic Story of Isle Royale National Park

Cover

Introduction

The island in history

A look at the landscape

The building blocks—rocks and minerals
     Volcanic rocks
     Sedimentary rocks
     Pyroclastic rocks

The way the rocks are stacked up
     A volcanic pile—the Portage Lake Volcanics
          Rock Harbor—Tobin Harbor area
          Washington Harbor area
     An ancient alluvial fan—the Copper Harbor Conglomerate
     Tilting and breaking the rocks
     Isle Royale—a small piece of the big puzzle

What happened when?
     Time as a geologic concept
     What was there before—the pre-Keweenawan
     The rocks of Isle Royale—the Keweenawan
     The missing chapters
     The glaciers take over
          Glacial effects on the land
          Glacial effects on lake levels

Some minerals of special interest
     Native copper—widespread but not abundant
     Chlorastrolite—Michigan's state gem
     Prehnite—the little pink pebbles
     Agate—an array of colors

What the future holds?

A word of thanks

Definition of terms

References and additional reading

SHADED RELIEF MAP OF ISLE ROYALE NATIONAL PARK, MICHIGAN. (Prepared by A. J. Burgess).

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UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY

Library of Congress Cataloging in Publication Data
Huber, Norman King 1926-
The geologic story of Isle Royale National Park.

(Geological Survey Bulletin 1309)
Bibliography: p. 64-66
Supt. of Docs. No.: I 19.3:1309
1. Geology—Michigan—Isle Royale National Park—Guide-books. I. Title. II. Series: United States. Geological Survey. Bulletin 1309.
QE75.B9 [QE126.18] 557.3'08s [557.74'997] 75-619126

ISBN 0-932212-31-X — First Edition April 1983
Reprinted March 1986

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