university of

Connecticut

ibraries

BOOK 553.5.B68 c. 1 BOWLES # STONE INDUSTRIES

3 T1S3 D013b7flb 3

Digitized by the Internet Archive

in 2009 with funding from

Boston Library Consortium IVIember Libraries

http://www.archive.org/details/stoneindustriesdOObowl

THE STONE INDUSTRIES

b

.6Q

THE STONE INDUSTEIES "

Dimension Stone Crushed Stone

Geology Technology Distribution Utilization

BY

OLIVER BOWLES

Supervising Engineer, Bxiilding Materials Section United States Bureau of Mines

Second Edition

McGRAW-HILL BOOK COMPANY, Inc.

NEW YORK AND LONDON

1939

Copyright, 1934, 1939, by the McGraw-Hill Book Company, Inc.

PRINTED IN THE UNITED STATES OF AMERICA

All rights reserved. This book, or

parts thereof, may not be reproduced

in any form without permission of

the publishers.

THE MAPLE PRESS COMPANY, YORK, PA.

PREFACE TO THE SECOND EDITION

Since the first edition of this volume appeared, the stone industries have suffered the most severe depression in their history. Now they are emerging toward a more normal rate of production, and there is definite prospect of increasing activity in building which should promote further gains. In this new edition most of the tables have been revised to show the latest available figures, and corresponding changes have been made in the text to embody the most recent data.

Centers of production have shown so Httle change during recent years that only minor corrections were needed. The sections on technology of quarrying and fabrication as covered in the first edition were based largely on the author's personal observation and study of hundreds of quarries and stone-finishing mills, and they reflect modern practice so comprehensively that little revision was required. Although refinements in equipment and methods are constantly in evidence, no fundamental modifications have occurred since 1934; therefore, the portrayal of condi- tions as set forth in the new edition approximates a true picture of the stone industries as they exist today.

Oliver Bowles. Washington, D. C, January, 1939.

PREFACE TO THE FIRST EDITION

No book adequately covering the stone industries has been available recently. Building stones were described many years ago by Dr. George P. Merrill in his well-known volume, Stones for Building and Decoration, the third edition of which appeared in 1910 and is now out of print. The venerable doctor was planning a much-needed revision, but his plans were cut short by his sudden death in 1929. Other books, such as E. C. Eckel's Buildijig Stones and Clays and C. H. Richardson's volume of the same title, are valuable for certain phases of the stone industries. Various bulletins on granites, marbles, and slates by T. Nelson Dale contain a wealth of detailed information, chiefly of geological import. Bulletins of several State geological surveys describe the stone resources and developments of their States quite thoroughly, but few have been published during recent years. Certain textbooks for engineers and architects contain brief and frequently quite inaccurate references to stone as a material of construction. None of the publications mentioned presumes to cover the many ramifications of the stone industries; the purpose of this volume is to fill this gap in American technical literature.

The author began his studies of the stone industries in Minnesota in 1912; and during the years since 1914, as a quarry specialist of the United States Bureau of Mines, he has visited and made intimate exami- nations of hundreds of quarries and mills scattered throughout many States. Results of successive detailed studies were embodied in a series of reports, several of which are now out of print. The background of first-hand knowledge thus gained was the chief incentive that urged him toward the laborious task of compiling this book.

Acknowledgment is made to the officials of the United States Bureau of Mines for permitting wide reference to its published information. Grateful acknowledgment is rendered to many who have assisted in preparing the material. In presenting a broad subject in a comprehen- sive manner innumerable occasions for errors occur, and while mis- statements may still remain, review by competent authorities and repeated revisions have greatly minimized this liability. The author desires to make special mention of noteworthy service by Harold Ladd Smith of Proctor, Vt.; J. B. Newsom of Bloomington, Ind.; J. L. Mann and R. M. Richter of Bedford, Ind.; Charles H. Behre of Evanston, 111.; W. S. Hays of Philadelphia; Lawrence Childs and Jules Leroux of New York, and Societe Anonyme de Merbes-Sprimont, Brussels, Belgium. Several quarry operators have kindly reviewed sections of the book

vili PREFACE TO THE FIRST EDITION

relating to their industries. The chapters devoted to crushed and broken stone involved so much detail regarding deposits and their geology that the services of State geologists were enlisted for review and comment. The author desires to express to them his keen appreciation of their most helpful and hearty cooperation. To Paul M. Tyler, Paul Hatmaker, and H. Herbert Hughes, associates of the author in the United States Bureau of Mines, acknowledgment is due for many helpful suggestions. Miss A. T. Coons of the Bureau, whose intimate knowledge of the stone- producing industries is widely recognized, supplied valuable comment and advice. To my wife, Eva H. Bowles, grateful acknowledgment is made for assistance in proof reading, and to my sons, George and Edgar, for corrections and revisions of certain sections.

Oliver Bowles. Washington, D. C. July, 1934

CONTENTS

Page

Preface to the Second Edition v

Preface to the First Edition vii

Introduction xiii

PART I

GENERAL FEATURES OF THE STONE INDUSTRIES

CHAPTER I Extent and Subdivision 3

Extent of the Industry — Major Divisions of the Industry — Varieties of Stone Used

CHAPTER II

Minerals and Rocks 5

Distinction between Rock and Stone — Relation of Rocks to Minerals — Rock-forming Minerals — Classification of Rocks — General Distribution of Rocks in the United States

CHAPTER III

Factors Governing Rock Utilization 8

Rock Qualities on Which Use Depends — Importance of Other Factors than QuaUty — Available Markets — Diversification of Products — Transportation Facilities — Production Costs

CHAPTER IV

Prospecting and Development II

Prospecting — Stripping— General Methods of Operation — Bibliography

PART II DIMENSION STONE

CHAPTER V

General Features of Dimension-stone Industries 23

Definition of Dimension Stone — Principal Uses — Requisite QuaUties of Dimension Stone — Adaptations of Raw Materials to Use — Complexities in Marketing — Royalties

CHAPTER VI

Limestone 33

Definition: — Origin — Physical Properties — Varieties — Qualities on Which Use Depends — Uses — Industry by States — Occurrences of Travertine — Quarry Methods — MiUing Methods — Limestone Products — Cost of Quarry- ing and Manufacture — Waste in Quarrying and Manufacture — Utilization of Waste — Limestone Marketing — Bibliography

X CONTENTS

Page CHAPTER VII

Sandstone 67

Varieties — Composition — Size and Shape of Grains — Cementation — Color — Porosity — Uses — Production — Industry by States — Quarry Methods — Quarry Processes — Yard Service — Sandstone Sawmills and Finishing Plants — The Bluestone Industry — Waste in Sandstone Quarrying and Manufac- ture— Bibliography

CHAPTER VIII

Granite 103

General Character — Mineral Composition — Chemical Composition — Physi- cal Properties — Varieties — Related Rocks — Structural Features- — Uses — Distribution of Deposits — Industry by States — Quarry Methods and Equip- ment— Milling Methods and Equipment — Market Range — Imports, Exports, and Tariffs — Prices — Bibliography

CHAPTER IX

Marble 168

History — Definition — Composition — Origin and Varieties — Physical Prop- erties— Jointing or Unsoundness — Chief Impurities of Marble — Uses — Dis- tribution of Deposits — Production — Industry by States — Quarry Methods and Equipment — Transportation — Equipment and Operation in Mills and Shops — Waste in Quarrying and Manufacture — Marketing Marble — Imports and Exports — Tariff — Prices — Bibliography

CHAPTER X

Slate 229

Definition — Origin — Mineralogical Composition — Chemical Composition — Physical Properties — Structural Features — Imperfections — Uses — History of Industry — General Distribution — Production — Industry by States — General Plan of Quarrying — Quarry Operations — Quarry Methods — Yard Transportation — Manufacture of Roofing Slate — Storage of Roofing Slate — The Art of Roofing with Slate — Manufacture of School Slates — Manufacture of Mill Stock — Slate Floors, Walks, and Walls — Crushed and Pulverized Slate Products — Waste in Quarrying and Manufacturing — Tests and Specifications — Marketing — Imports and Exports — Tariff — Prices — Bibliography

CHAPTER XI

SOAPSTONE 290

Composition and Properties — History — Uses — Origin and Occurrence — Quarry Methods — Milling Processes — Marketing — Rocks Related to Soap- stone — Bibliography

CHAPTER XII

Boulders as Building Materials 296

Origin and Nature of Boulders — Stone Fences — The Use of Boulders in Buildings

CHAPTER XIII

Foreign Building and Ornamental Stones 301

Scope of Discussion — Imports of Stone — Foreign Limestones — Foreign

CONTENTS XI

Page Sandstones — Foreign Granites — Foreign Marbles — Foreign Slates^ — Bibliography

CHAPTER XIV

Miscellaneous Rocks and Minerals Used for Building and Ornamental

Purposes 342

Agalmatolite — Alabaster — Amazonite — Catlinite — Clay — Diatomite, Trip- oli and Pumice — Fluorite — Jade — Labradorite — Lapis-lazuli — Malachite and Azurite — Meerschaum — Mica Schist — Porphyry — Quartz — Snow and Ice — Sodalite — Bibliography

CHAPTER XV

Deterioration, Preservation, and Cleaning of Stonework 348

Deterioration of Stone — Preservation of Stone — Cleaning Stone — Bibliog- raphy

PART III CRUSHED AND BROKEN STONE

CHAPTER XVI

General Features of the Crushed-stone Industries 371

History — Types and Values of Stone Used — Crushed Stone and Dimen- sion Stone Contrasted — Uses of Crushed Stone — Competition — Markets — Transportation — Prices — Royalties — Capital Required

CHAPTER XVII

Crushed and Broken Limestone 377

Types of Stone Included — Extent of Industry — Uses of Crushed and Broken Limestone — Uses for Which Physical Properties Are Most Important — Uses for Which Chemical Properties Are Most Important — Uses of Dolomite and High-magnesian Limestone — Industry by States — Quarry Methods and Equipment — Bibliography

CHAPTER XVIII

Crushed and Broken Stone Other Than Limestone 473

General Features — Uses — General Distribution and Value — Industries by States — Quarry Methods and Equipment — Marketing — Bibliography

Index 493

INTRODUCTION

Stone, the foundation and superstructure of the everlasting hills, is the most abundant of all material things. It is the earth itself on which we live. Although widespread in occurrence to a point that breeds contempt, stone is used so extensively that it touches the extremes of human activity — from lowly shattered fragments trampled under foot to flawless statuary marbles that provide material for the highest forms of art. Between these two extremes stone and its products are essential to multitudes of industries; they take part in the affairs of practically every community and touch the life of nearly every person. To cover in detail so broad a field would far exceed the scope of a single volume, but an attempt is made to present a moderately comprehensive picture of the properties and characteristics of stone, the methods of removing it from its native beds and preparing it for use, its many applications in modern industry, production centers at home and abroad, and the outstanding economic features of each branch of this far-reaching industry.

Remarkable progress has been made in the quarrying and utilization of stone. Its application to practical use was one of the oldest human activities, extending far back before the earliest records, for the name "stone age" is applied to that period of history of which knowledge is conveyed to us only by crude tools and implements of stone fashioned by the aborigines. Neolithic man, using a crooked reindeer antler as a mining tool, dug flint balls from the chalk cliffs of England and shaped them into spear heads or other implements. During later periods American cliff-dwellers constructed crude homes with walls of stone. The slow progress made through long ages from these primitive begin- nings makes interesting chapters in ancient history but has little bearing on the stone quarrying of today. Development of the industries in their present scope has been comparatively recent. From caverns and shelter- ing slabs of rock constituting the earliest human habitations to stately mansions of cut and polished stone is a long journey, and every step of progress has been marked by accelerated speed. Thus, although the industries have existed for many centuries, the greatest advances in manufacture and use have been crowded into the last fifty years. To give a true picture of the status of these industries today is the purpose of this book.

PART I GENERAL FEATURES OF THE STONE INDUSTRIES

CHAPTER I EXTENT AND SUBDIVISION

Extent of the Industry. — Stone production is the most widespread of all industries in this country except agriculture, for rock deposits are exploited in every State and in a great majority of the counties. In the United States the average annual production of stone of all kinds, including slate, from 1927 to 1931, was more than 176,500,000 short tons, with an annual value exceeding $216,300,000. About 2,800 quarries and mines are in operation, and the number of employees in them and in directly associated plants is approximately 90,000.

Delivery of the enormous tonnage of stone to innumerable markets is an important transportation item, involving rail, water, and truck haulage. Coal and oil burned in quarries, mills, cement plants, and lime kilns constitute an appreciable part of the fuel production of the country, and the machinery and explosives used create an extensive market for factory products. Thus, through its wide scope and complex ramifi- cations stone holds a dominant place in the Nation's industry and exerts a pronounced influence on national growth and development.

Major Divisions of the Industry. Dimension Stone. — The oldest use of stone and the one that has become increasingly important through the centuries is for building purposes. At first, rough walls were built of scattered boulders, but with increasing knowledge of the use of tools stone was quarried from solid ledges. Before the age of explosives and before steam and compressed air were utilized quarrying was slow and laborious; nevertheless, the pyramids and obelisks represent remarkable engineering skill. These magnificent stone structures were built by innumerable slaves, whose labor extended over many decades. Since ancient times stone has been a favorite material for constructing the finest buildings. Growth and development in art and architecture have been expressed in noble structures, and we are indebted to the enduring nature of stone for the preservation of many invaluable records of past achievement.

The hewing of stone from its native beds with only the crudest hand tools made it too costly for use, except in temples, palaces, and similar structures. With the invention of explosives, the advent of steam power, and, later, the use of electricity and compressed air, blocks of stone were obtained with increasing ease, and rock became more and more widely available as a building material. From cathedrals, bridges, and other

3

4 THE STONE INDUSTRIES

great public works it has found its way to smaller and less pretentious structures, even to small one-family homes.

Dimension stone is used for other purposes than for building. In ancient times a pile of stones was raised as a memorial, and from this custom has developed the monument or headstone cut from suitable rock and carved with a fitting inscription. Stone blocks are also used for pav- ing streets and roads and for the manufacture of curbing. In addition, stone has many special uses, such as for electrical switchboards and blackboards.

Crushed Stone. — ^The use of crushed or broken stone developed much later than that of dimension stone. Stone sledged by hand, usually by convict labor, was used in road construction, and this use increased rapidly. With the invention of cement and with mass production made possible through explosives, power crushers, and screens the broken-stone branch of the industry grew with phenomenal speed. In 1886 the output of crushed and broken stone was smaller than that of dimension stone, while in 1930 it was thirty times as great. Concrete aggregate, road stone, and ballast are the principal products.

Stone Used in Manufacturing Processes. — For practically all the uses mentioned above, stone is employed crude and untreated. It may be shaped, polished, crushed, or ground, but its physical and chemical properties remain essentially unchanged. In many modern industries, however, stone undergoes physical and chemical changes, the final product being quite different from the raw material in both form and composition. Outstanding examples are limestones manufactured into cement, lime, or calcium carbide; dolomite made into refractories; and crushed sandstone fused with other products into glass.

Varieties of Stone Used. — The more common rocks used in com- merce are granites and related igneous rocks, limestones, marbles, slates, and sandstones. Soapstone also is included as a branch of the dimension- stone industry. Many rocks in commercial use do not properly belong to any of the foregoing groups. When employed as dimension stone they usually are classed with one of the major groups; when used in crushed or broken form they are considered a miscellaneous group.

CHAPTER II MINERALS AND ROCKS

Distinction between Rock and Stone. — While the words "rock" and "stone" are often regarded as synonyms, there is a definite distinction in their meaning. The term "rock" is applied to a geologic formation in its crude form as it exists in the earth. "Stone" is more properly applied to individual blocks, masses, or fragments that have been broken from their original massive ledges for application to commercial use. Therefore, in chapter I the term "stone" is generally employed because reference is made to manufactured products; in Chapter II "rock" is used because the text relates to geologic formations as they exist in nature before exploitation for economic use.

Relation of Rocks to Minerals. — To understand rocks properly one should be acquainted with minerals, because rocks consist of them. The relationship may be brought out most clearly by comparing minerals with letters and rocks with words. Just as there is a word of one letter, the article "a," so we have rocks made up essentially of a single mineral; for example, limestone, which is the mineral calcite, or sandstone, a form of quartz. Some words are made up of many letters, and in like manner some rocks consist of several minerals; thus, granite consists of feldspar, quartz, mica, and sometimes small quantities of hornblende, magnetite, pyrite, garnet, and other minerals. A knowledge of rock-forming miner- als is therefore a necessary preliminary to a well-balanced concept of rocks. It may be mentioned, however, that some rocks consist wholly or partly of natural glass or volcanic dust — materials that cannot properly be classed as minerals.

Rock -forming Minerals. — It is assumed that the reader or student who attempts to gain knowledge of the stone industries through these pages has had at least an elementary course in mineralogy. Those who lack this advantage or who desire to refresh their minds on the subject are referred to textbooks or handbooks on mineralogy, because space will not permit descriptions of minerals or means of their identification.

The important minerals in igneous rocks are feldspars, quartz, mica, hornblende, and augite. Those most abundant in sedimentary rocks are calcite, dolomite, and kaolinite (clay). Minor constituents include chlorite, epidote, tremolite, actinolite, olivine, serpentine, garnet, sphene, zircon, talc, pyrite, marcasite, magnetite, hematite, limonite, and apatite.

5

6 ' THE STONE INDUSTRIES

Classification of Rocks. — Rocks are classified according to their origin into three great groups — igneous, sedimentary, and metamorphic. Igneous rocks are those that originated from molten masses or magmas more recently regarded as high-temperature solutions. Semiliquid mag- mas deep within the earth cool more or less slowly as they approach the surface until a condition of solidification is attained. The nature of the resulting rock depends on both the composition of the magma and the rate of cooling. Magmas that cool very slowly at great depth tend to form coarse-grained rocks, such as granites and gabbros, because slow cooling ordinarily promotes coarse crystallization. On the other hand, rapid-cooling magmas form fine-grained rocks, such as basalt and aplite. Some rocks, consisting of relatively coarse crystals scattered throughout a fine-grained ground mass, are known as the "porphyries."

Sedimentary rocks are sometimes referred to as "stratified," because they are formed of sediments laid down in successive strata or layers. The materials of which they are formed are derived from preexisting rocks. Processes of rock decay or disintegration on the surface of the earth, though very slow, are continuous and produce stupendous results through centuries and geologic ages. Alternate frost and heat open innumerable fractures in rocks; chemical agents of the atmosphere or of surface and subterranean waters penetrate them and dissolve part of the rocks. Rain, streams, waves, tides, and glaciers loosen the shattered fragments, grind them up, and transport them far from their sources. Wind, too, is an agent of erosion and transportation. . Millions of tons, even cubic miles, of rock are disintegrated by these various agencies and carried away to oceans, lakes, and river beds where they are deposited as sediments. In addition to these products of rock decay, myriads of organisms that inhabit the oceans or lakes secrete calcium carbonate or silica from the water to form their shells, and their skeletal remains add to the accumulations of rock-forming material. Thus, three great proc- esses— rock disintegration, transportation, and redeposition — are now and have been at work for ages. These processes — aided, as has been stated, by organic agencies — have formed most of the sedimentary rocks. Four major types are thus formed — conglomerate, sandstone, shale, and limestone.

Metamorphism means change in form. Rocks of either igneous or sedimentary origin that have been changed profoundly during the course of their existence are known, therefore, as "metamorphic rocks." The chief agencies that produce such changes are pressure, heat, and chemical reaction. Rocks deep in the earth may become plastic under great pres- sure and high temperature and by earth movement may be tilted or folded into complex forms with a banded or schistose structure. Pressure may cause recrystallization, and thermal waters may dissolve, transport, and reprecipitate many minerals. Thus, new rocks may be formed of a

MINERALS AND ROCKS 7

texture and composition quite different from those of unaltered igneous or sedimentary types.

The principal igneous rocks are granite, aplite, syenite, diorite, gabbro, basalt, diabase, rhyolite, and tuff. Sandstone, conglomerate, shale, limestone, and dolomite constitute the group of sedimentary rocks. The metamorphic group includes gneiss, schist, quartzite, slate, marble, and soapstone. Most of the above-named varieties are defined and described in some detail in various following chapters devoted to discussion of their distribution and exploitation. For those desiring a more thorough treatise several textbooks on petrography are available.

General Distribution of Rocks in the United States. — As may be inferred from the foregoing brief description of the origin of rocks, their occurrence is directly related to the geologic history of each region. The Appalachian district of eastern United States, extending from Maine and Vermont to Georgia, is a rugged, mountainous region that has suffered more or less extreme folding or metamorphism ; therefore, as one would expect, metamorphic rocks, such as crystalline marbles, slates, gneisses, and schists, are to be found there. Throughout the district many unal- tered rock areas also occur and comprise important deposits of granite, diabase, gabbro, sandstone, and limestone.

Between the Appalachian belt and the Rocky Mountains is a vast area in which characteristic metamorphic rocks, such as marble, slate, and gneiss, occur rarely because this is primarily a region of flat-lying sediments that have been distorted very little by mountain-building forces. Nearly horizontal limestone and sandstone beds are the charac- teristic commercial rocks of the area comprising the eastern portions of West Virginia, Kentucky, and Tennessee; all of Ohio, Indiana, Illinois, Iowa, Nebraska, North and South Dakota, Kansas, Mississippi, Louisi- ana, Florida, Oklahoma, southern Minnesota, Wisconsin, and Michigan; and most of Missouri, Arkansas, and eastern Texas. Isolated areas of granite occur in Wisconsin, Minnesota, Missouri, South Dakota, Arkan- sas, Oklahoma, and eastern Texas.

West of the prairie country is another belt, the Rocky Mountain area, in which the rocks are greatly crumpled and folded. Here again the igneous and metamorphic rocks are abundant. This belt passes through Idaho, Montana, Colorado, and New Mexico. Some of the granites, gneisses, and marbles where accessible, have commercial importance. From the Rocky Mountains to the Pacific Coast igneous rocks, of both the granitic type and the more basic varieties such as basalt and gabbro, are very common. Regional metamorphism has produced marbles and slates, but many unaltered limestones and sandstones are found. Vul- canism of comparatively recent geologic age characterizes much of this great western area; and the resulting rocks, such as lava, rhyolite, andesite, and volcanic tuff, are common. Such rocks are rarely found in the Eastern or Central States.

CHAPTER III FACTORS GOVERNING ROCK UTILIZATION

Rock Qualities on Which Use Depends. — Although rock is the most abundant of all material things only a small fraction of the occurrences at or near the earth's surface is fit for commerce. Requisite qualities which are variable, depending upon the use to which the stone is to be applied, are covered in following commodity chapters.

Importance of Other Factors Than Quality. — Although utilization depends to a marked degree on physical or chemical adaptability, other factors are equally important. Owners of rock deposits are prone to assign too much importance to the quality of their materials without adequate attention to certain economic factors that affect the success or failure of any stone enterprise. For example, building-stone deposits of most excellent quality would be valueless if situated in northern Alaska because the cost of transportation to the nearest market would be prohibitive.

Available Markets. — A study of market outlets for the type and quality of stone available is essential to most successful operation. If the quarry product is crushed stone or similar material that commands a low price per ton, local markets are more important than those at a distance ; favorable transportation, however, may extend the market range, which is also influenced directly by production costs. A low-cost plant can compete in a wider area than a high-cost plant handling the same class of commodities. Present and probable future demand should be con- sidered in relation to the production capacity of plants handling com- petitive materials within the economic shipping radius. For relatively high-priced products, such as ornamental granites and marbles, trans- portation is a less formidable item in the total delivered price, and the market range may be nationwide. A wide market area, however, brings them into competition with all other similar materials ; successful market- ing depends upon quality, workmanship, popularity with consumers, prompt delivery, and aggressive salesmanship.

Diversification of Products. — Practically every quarry and pit can produce a variety of grades and classes of materials, A slate quarry may yield roofing slate, structural and electrical slate, blackboards, roofing granules, and slate flour. A granite quarry may provide monumental stone, cut stone, ashlar, rubble, paving blocks, curbing, and crushed stone. Many operators tend to concentrate on one product and discard as waste

FACTORS GOVERNING ROCK UTILIZATION 9

any material that can not be applied to this particular use. For profitable operation in a competitive market diversification of production is desirable, and a market should be sought for all types of materials avail- able in a quarry. Although a certain amount of waste is inevitable the enormous piles of rejected stone in many quarry regions indicate that an inquiry might profitably be conducted into the possibility of more extended utilization of by-products.

Transportation Facilities. — Stone is heavy, and the haulage charge is a considerable proportion of the delivered price; for the lower-priced products it may be the chief item of cost at point of consumption. Trucks now handle local delivery almost universally, and the cost depends primarily on the nature of the roads. They are also being employed to an ever-growing extent for distant delivery, the main incentives being the increasing mileage of hard-surfaced roads and the increasing speed of travel, as trucks carrying 6 to 8 tons now attain a speed of 35 to 50 miles an hour.

For distant markets rail or water facilities are essential. Even though the rock is of superior quality, deposits far from railroads may have little value. Such markets are controlled largely by freight rates. Wherever possible commodity rates should be established. Many railroad companies prefer to haul stone because its imperishable nature permits shipment in open cars.

Transportation by water is becoming increasingly important, as indicated by the recent completion of a deep waterway on the Ohio River, and the great increase in quantities of limestone, gypsum, and cement now conveyed by this means. Attention may be directed to increasing tonnages of limestone carried on the Great Lakes: 13,933,378 tons in 1927; 15,679,551 tons in 1928; and 16,269,612 tons in 1929. Water rates are usually lower than rail rates.

Production Costs. — The success of any stone enterprise depends largely on maintaining low production costs. High-cost plants can exist in a competitive market only where some favorable circumstance, such as superior quality of the stone, by-product utilization, effective sales organization, or rapid delivery, gives them an advantage. Quarrymen must therefore keep abreast of the times in efficiency of methods and equipment. Today low cost depends primarily on plant mechanization.

Only by using some effective system of accounting can a knowledge of costs be obtained. Hence systematized cost-keeping is to be regarded as an important economic factor in conducting any stone enterprise.

Competitive Products. — Stone is meeting increasing competition from metals and synthetic products. Aluminum is employed in place of stone for both interior and exterior use. The movement toward all- metal construction is attracting much attention, while glass, enameled steel, and other ceramic products are finding new and important

10 THE STONE INDUSTRIES

uses. Alert stone producers are watching all such trends with exceeding care.

Labor and Wages. — Usually the largest single item in production cost is the amount paid in wages. Abundance or scarcity of labor, the prevailing wage level, and living conditions have an important influence on quarry methods. Scarcity of labor or abnormally high wages encour- age more complete mechanization. Most stone producers recognize the value of giving special attention to the health, safety, and comfort of their workers, for by so doing they build up a personnel of steady employees, a condition advantageous to both employer and laborer.

CHAPTER IV

PROSPECTING AND DEVELOPMENT PROSPECTING

Development work should not be started on a deposit without reasonable assurance of an available mass of rock sufficiently high in quality and abundant in supply for profitable exploitation. Prospecting is often found advantageous in quarries that have long been in operation ; it is, in fact, a continuous activity with some companies, which enables them to determine the extent of reserves and to plan future developments intelligently.

If the rock appears in bare outcrop, usually a rough estimate of its quality and extent can readily be made. Sedimentary rocks are, as a rule, fairly constant in composition throughout the same bed or zone of deposition, and the greatest variations are found in passing from one bed to another; therefore, all beds that may be included in a quarry are usually sampled. A cliff or escarpment along a stream or gulley is especially valuable, because it provides a cross section which permits tests of quality at various levels. If such a cross section is not available in nature, test holes are drilled at such intervals as will supply adequate data on the whole area under consideration.

The prospecting method is governed to some extent by the type of operation. If the chemical composition of the rock is of primary impor- tance, as in furnace flux, lime, or cement materials, churn-drill cuttings will supply material for chemical analyses. Drill cuttings are sampled at regular intervals, for example, every 5 feet, and an exact record is kept of the drill hole and depth at which each sample is taken. The distance between samples is governed by the uniformity of the rock. Where analyses lack uniformity samples are taken at closely spaced points while in rock of more constant composition they are obtained at wider intervals.

For dimension-stone and most crushed-stone uses the physical are more important than the chemical properties of a rock. Dimension stone must be free from cracks, of uniform texture, of attractive color, and for some uses capable of taking a polish. For crushed-stone uses rock must have satisfactory strength, soundness and low absorption. Churn-drill samples can not be used for testing these qualities. Core drilling is desirable because it not only provides data on the structure and extent of the deposit, but this type of drill cuts out cylindrical masses suitable for making physical tests. Diamond core drills which are in common

11

12 THE STONE INDUSTRIES

use, consist of a rotating steel drum with black diamonds (carbonados) set in its lower edge. Some of the newer types of extremely hard alloys are now being used as substitutes for diamonds in cutting softer rocks. Shot drills also give satisfactory service; cutting is done with a rotating steel drum fed with steel shot as an abrasive. Prospect-drill cores are usually 3 inches, or smaller, in diameter.

The position and spacing of holes are governed by the nature of the rock. Usually the geology of a region is studied thoroughly. General information regarding the geology usually may be obtained from Federal or State geological reports, although some companies employ trained geologists to work out the structure and relationships of all rock forma- tions associated with an operating or prospective quarry.

No definite rules can be given for the position or arrangement of holes. In flat-lying beds of uniform thickness and fairly constant composition they may be spaced at wide intervals — 100, 500, or 1,000 feet; where rocks are folded or tilted, or where changes in composition or structure occur within short distances, they should be spaced more closely. Detailed maps are made for complex deposits. From a map constructed after careful study of exposures the position, thickness, and slope of beds may be determined with fair accuracy. In bedded deposits drill holes usually are projected approximately at right angles to the bedding. To intersect steeply dipping beds inclined drill holes may be required; for this purpose a core drill has advantages over a churn drill, for it may be used to drill holes at any angle, even in a horizontal position if so desired, while except in rare instances churn-drill holes are vertical.

Accurate records of every drill hole are kept, and a map is made showing its exact location. As each core section is removed it is marked, recorded, and stored for future reference. Some large companies main- tain fireproof storage sheds for prospect-drill cores.

The direct cost of sinking 5}^- to 6-inch churn-drill holes in limestone is 20 to 60 cents a foot. These figures apply to constant drilling by experienced workmen. Drilling harder rocks, such as trap rock and granite, is more expensive, the cost ranging from $1.50 to $6.00 a foot. Core drilling with shot or diamond drills costs $3.00 to $5.00 a foot, depending on the nature of the rock and drilling conditions.

When the extent of a stone deposit is known, the approximate ton- nage may easily be determined. Rocks vary somewhat in weight. Merrill^ compiled tables of the weight of many building stones. The average of 68 granites was 166 pounds per cubic foot; of 36 limestones, dolomites, and marbles, 161 pounds; of 76 sandstones, 141 pounds; and of 4 trap rocks, 182 pounds. Sandstones are the most variable because they differ so much in porosity.

1 Merrill, G. P., Stones for Building and Decoration. 3d ed., John Wiley & Sons, Inc., New York, 1910, pp. 498-507.

PROSPECTING AND DEVELOPMENT 13

To determine the approximate number of short tons available in a limestone deposit the length, width, and depth in feet, as proved by- prospect drilling or other methods, may be multiplied and this product is then multiplied by the average weight per cubic foot (161 pounds) and divided by 2,000. For granite or sandstone the corresponding figure for weight per cubic foot may be substituted. Generally it is deemed unwise to expend the large sum necessary to establish quarries and finish- ing plants unless as a result of prospecting a reserve of good rock suflficient for at least 20 years' operation is assured. Some companies operating dimension-stone deposits open up quarries at moderate expense and sell their products in rough blocks until the quality of the rock is proved, marketability established, and a definite income assured. In due time finishing mills may be built and equipped.

The determination of overburden is a phase of prospecting. Both the depth and nature of overlying material, whether sand, gravel, clay, or inferior rock, may be learned by drilling or trenching.

STRIPPING

Nature and Thickness of Overburden. — Stripping is the process of removing the overburden of clay, gravel, or sand from the rock surface. Many deposits of marketable rock are overlain with inferior quality rock, which in a sense may be regarded as overburden. However, as methods of removing solid rock, whether barren or useful, are quite distinct from those employed in handling soil, removal of inferior waste rock is to be classed as a quarrying rather than a stripping problem.

Most stone producers are interested in stripping. In certain places quarries are worked in rock formations that appear in bare outcrop, and fortunate owners of such quarries may view their neighbor's stripping problems with a certain degree of complacence. Most commercial rock deposits, however, are covered with varying depths of rock debris. Indeed, the absence of all overburden is not always an unmixed blessing. The writer has observed granite areas where 10 feet or more of soil has preserved the rock almost to the surface, while other parts of the area that were in bare outcrop were altered and discolored too greatly for monumental use to depths of 4 to 8 feet. Removal of such rock as waste is moreover more costly than removing several feet of soil.

The depth of overburden ranges from a few inches to 10, 20, 30, and in exceptional instances even 40 or 50 feet. Likewise, the nature of mate- rials composing it is variable. It may be easily disintegrated loam, sticky plastic clay, sand, gravel, boulders, or even a hardpan that may require blasting.

Stripping usually is a problem of greater magnitude in the crushed than in dimension-stone industries. For crushed-stone uses a great volume of stone must be handled; many quarries produce thousands of

14 THE STONE INDUSTRIES

tons a day. This great bulk of material demands rapid widening of quarry walls, and stripping may become continuous. The dimension- stone branches of the industry handle relatively higher-priced products per ton which require much more labor in preparation, and the tonnage produced is correspondingly lower. Working at much greater depths is justified by the more valuable products, and 5 or 10 years may elapse before a new pit is started or a new bench opened.

Clean Stripping. — For certain classes of quarries clean stripping is essential; for others it is immaterial. Purity has first importance for stone applied to chemical uses. Silica and alumina are most undesirable impurities in limestone for lime manufacture and for furnace flux, and such impurities are the chief constituents of the overburden. Clean stripping is therefore essential at such quarries. On the other hand, in the manufacture of portland cement clay is added to the limestone to obtain a proper mixture; hence, if some clay is quarried with the rock and proper care exercised in subsequent addition of clay, no detriment to the product will ensue. Similarly, in dimension-stone production surface debris will not harm the product ; it will be separated from quarry blocks in due course and removed with other quarry waste. In best quarry practice, however, as much of the overburden as can be handled conveniently is removed before underlying rock is quarried.

Stripping Difficulties Due to Erosion Cavities. — Limestone and marble are exceptionally difficult to strip because the slow erosion of circulating water follows joints and cracks and thus wears away the rock surface very irregularly, leaving numerous tortuous cavities filled with clay, sand, or gravel. Generally the upper 10 or 20 feet consists of knobs or pinnacles of rock standing in a mass of clay. Granites, sandstones, and trap rocks are also subject to erosion, and quite irregular surfaces may result; usually, however, they are comparatively smooth and regular. Erosion cavities cause much difficulty and greatly increase the cost of stripping.

Stripping Methods. — No quarry process is more variable than strip- ping. The nature and depth of overburden and conditions of its removal and disposal show wide differences from quarry to quarry. Therefore, equipment and methods commonly employed are subject to similar variations, which are discussed briefly in the following paragraphs.

Hydraulic Method.— The hydraulic method, which simply involves washing the overburden away with a stream of water under pressure, is the cheapest and most effective. Conditions for its successful use are, however, somewhat exacting, the chief requirements being as follows:

1. An ample supply of water must be obtainable. An average of about 10 tons of water is needed for each ton of overburden removed. However, the same water may be used repeatedly if settling basins are provided for clarification.

PROSPECTING AND DEVELOPMENT

15

2. A favorably situated waste-disposal area is essential. The best conditions exist where the soil may be washed back from the quarry face or laterally into ravines or basins where it may remain.

3. Hydraulicing is effective only where the overburden is friable enough to be washed down and carried away with a stream of water. The presence of hardpan or of numerous heavy boulders may cause great difficulty and justify the use of other methods.

The equipment required for hydraulic stripping includes a pump, a pipe line, a mounted nozzle or monitor, and possibly an additional dredging pump, together with the necessary source of power. A great advantage of the hydraulic method is the wide range of action and ease of moving from one point to another. Its adaptability for removing clay and sand from irregularly eroded surfaces is an outstanding advantage.

1 I . 1 A rugged ruck builaet stripped b> the hj draulic method.

Soil that could be removed only with great difficulty by other means is washed out by