Alexander Winchell.

Geological studies, or, Elements of geology, for high schools, colleges, normal, and other schools online

. (page 1 of 40)
Online LibraryAlexander WinchellGeological studies, or, Elements of geology, for high schools, colleges, normal, and other schools → online text (page 1 of 40)
Font size
QR-code for this ebook


THE LIBRARY

OF

THE UNIVERSITY
OF CALIFORNIA

LOS ANGELES



The RALPH D. REED LIBRARY
->

DEPARTMENT OF GEOLOGY
UNIVERSITY OF CALIFORNIA

LOS ANGELES, CALIF.



/) ^ '~i

&*&*-



Iff?



GEOLOGICAL STUDIES;



OR,



ELEMENTS OF GEOLOGY.



FOR



HIGH SCHOOLS, COLLEGES, NORMAL, AND OTHER SCHOOLS.



PART I. GEOLOGY INDUCTIVELY PRESENTED.
PART II. GEOLOGY TREATED SYSTEMATICALLY.



WITH 367 ILLUSTRATIONS IN THE TEXT.



BY ALEXANDER WINCHELL, LL.D.

PROFESSOR OF GEOLOGY AND PALAEONTOLOGY IN THE UNIVERSITY OF MICHIGAN, FOR-
MERLY DIRECTOR OF THE GEOLOGICAL SURVEY OF MICHIGAN, AUTHOR OF
" GEOLOGICAL EXCURSIONS," FOR ELEMENTARY SCHOOLS, ALSO
OF ' 4 SKETCHES OF CREATION," "WORLD LIFE,' 1
ETC., ETC.



SECOND EDITION



CHICAGO:
S. C. GRIGGS AND COMPANY.

188T.



COPYRIGHT, 1886,
BY S. C. GRIGQS AND COMPANY.



Geology
Library



*



m



"THE diffusion of that which is specially named science has at the same
time spread abroad the only spirit in which any kind of knowledge can be
prosecuted to a result of lasting intellectual value." PROFESSOR JEBB.

"All the subjects which the sixteenth century decided were 'liberal' are
studies in books; but natural science is to be studied not in books, but in
things." PRESIDENT ELIOT.

"The genesis of knowledge in the individual must follow the same course
as the genesis of knowledge in the race."

"Every study should have a purely experimental introduction." HER-
BERT SPENCER.

"Were I dictator, I would drive all teachers of science out into the great
field of dead work; force them to go through all the gymnastics of original
research and its description, and not permit them to return to their libraries
until their note books were full of their own measurements and calculations,
sketch maps, and farm drawings, severely accurate, and logically classified,
to be then compared with those recorded in the books." JOSEPH P. LESLEY,






766287



PREFACE.



rj^HIS work on the elements of geology is intended as a guide
-L in the observation of nature, and a synoptical record of the
more important tacts and doctrines of the science. The reader
is supposed to be desirous of laying substantial foundations for a
geological education, and to have attained such mental develop-
ment as to require a text book more advanced than the Author's
"Geological Excursions." The method, as in that work, is an
appeal to the powers of observation; and the facts cited are the
most familiar and most accessible. Happily, the widespread
Drift of the northern portion of the continent brings to nearly
every student's door a body of phenomena so similar as to supply
an intelligible common starting point for a very large proportion
of the United States and Canada; while for students of the
southern states, any inconveniences may be easily overcome.
Though this method is believed to be unique, it is, without ques-
tion, the method which best comports with the order of develop-
ment of the mental faculties, and must prove most easy and
gratifying to the student. It is the application to geology of
those sound principles which have come into vogue among the
best modern teachers of the other sciences of nature. That it is
entirely practicable is shown by the personal experience of the
Author, and of many other teachers who have used the more
rudimental work above mentioned.

What there is among the universal phenomena of the Drift to 1
serve as the elementary data of geological science will perhaps be
best understood by turning over the earlier pages of the First
Part of the book. The Author does not, however, imagine the
pupil a mere recording instrument; but bears in mind the fact
that the dawn of reflection is simultaneous with the exercise of



v i PREFACE.

perception. The observer begins immediately to group phe-
nomena to generalize, and to inquire after those uniform
antecedents which science denominates causes. The Author
encourages this tendency by pausing occasionally to review, to
summarize, to induce a general principle, and even to theorize a
little. Thus, in the First Part, scientific method is unknown.
The science is growing up in the learner's mind simultaneously
and symmetrically in all its departments, just as it grew in the
intelligence of mankind.

A little later, after the nearest phenomena have yielded their
lessons, the learner is led from home to widen his observations.
Well, indeed, if the travel can be real, like the earlier excursions
into the neighborhood. But the impracticability of this, as a
rule, is offset, as far as possible, by graphical illustrations. In
many cases, it may be further offset by specimens, models, and
diagrams. These the school, or the teacher, or even the pupil
himself, may, to some extent, provide. As, after all, many
things can only be known from descriptions, the effort has been
made to have them intelligible.

The purpose to begin with the Drift has led to a more careful
study of common minerals and rocks than has heretofore been
undertaken in elementary works; but this feature, the Author
believes, requires no defence. On the contrary, he is already
assured that the tables provided for determinations of minerals
and rocks from their most obvious characters will receive a hearty
welcome; and will satisfy many longings to know something
more about the objects which are absolutely the most obtrusive
and familiar which we encounter.

The same purpose has led to a more particular study of some
common types of fossils than has ordinarily been thought appro-
priate. But this study has been restricted mainly to examples
widely distributed in the Drift, and therefore generally obtaina-
ble; and it has been pursued only far enough to illustrate how to
study fossils in a scientific way.

The outcome of the First Part is a somewhat chaotic and
undigested mass of facts and doctrines, buried in a considerable



PREFACE. vii

volume of verbiage. It does not, assuredly, supply the means
for a methodized apprehension of the elements of the subject.
But it supplies many fundamental facts, many great principles,
many impressions, many hints for personal observation, and many
impulses to continue. Far better for the student to get so much
than to leave school in total ignorance of a science which sus-
tains so important relations to industries, to culture, and to civili-
zation.

Part II is the complement of this. Here the whole body of
facts and principles is reduced to methodical re-presentation;
though the necessity of abridgment has led, in some of the
chapters, to mere references to the First Part, instead of recast-
ings of the matter. Here, too, the discussions of the several
topics are completed, and the various portions are adjusted to a
logical relation. The last chapter is a rapid historical sweep over
the whole range of terrestrial events. To a limited extent,
therefore, the book may be used for elementary reference. But
it must not by any means be conceived as intended for a manual.
The method of a manual is suited only for advanced students
and investigators. A very different method is demanded by be-
ginners. This is only to a limited extent even a "text book."
That term savors of an educational method which is obsolete and
repugnant. The present work is a guide to the study of nature,
and a synopsis of the elementary facts and principles of geolog-
ical science.

Because the work is elementary, it has been restricted almost
wholly to American geology. But no well beaten path has been
pursued. The recent additions to our knowledge of American
geology have greatly transformed the science, and the subject
has to be treated very much as if no elementary books had been
written. Recent investigations have placed us in possession of a
large body of information about the remote interior and the
Pacific slope, and the vast region north of our national boundary.
To this fresh information the author has attempted to give due
attention. It will be found a feature of the work, that it sur-
passes other elementary books in its presentation of western



PKEFACE.



geology, especially in its great features and its great historical
facts.

The author's obligations, of course, lie in every direction;
they are, indeed, too many to enumerate. But the effort has
been made to draw less on the writers of text books than on
original sources. To his publishers, his indebtedness and that of
the public is great, for that intelligent liberality which has
prompted them to demand, regardless of cost, the best style of
graphic illustration, and a perfection of mechanical execution
which will scarcely be found surpassed.

The author entertains the hope that he has here brought
within reach of his fellow-workers in the advancement of popu-
lar education some improved means for placing geological study
where of right it belongs side by side with the most esteemed
and most favored agencies of material prosperity, of civilization,
and of culture.

UNIVERSITY OF MICHIGAN, Ann Arbor, June, 1886.



PKEFACE TO A NEW EDITION.



THE exhaustion of the first edition of this work within six
months of its introduction into use is sufficient evidence of
its acceptability as an elementary guide to the science of geology.
Among the numerous opinions which have reached the author
respecting its method and matter, no one is seriously adverse,
while commendations are almost unlimited in number. Yet the
author begs to request teachers in schools where the time given
to geology is quite brief, to remember that the bulk of Part I.
results partly from the method of treatment; and that method is
chosen for the purpose of rendering the subject entertaining, and
building up a knowledge of it in a natural way. For a brief
course, Part I. may be taken by itself; and then Part II. may be
taken later. Also, the studies of fossil corals and shells in Part
I. may be postponed, as well as the palaeontological portions of
Part II. ; and these may be taken up subsequently as a course in
palaeontology.
FEBRUARY, 1887.



CONTENTS.



PART I. FIELD STUDIES;

OB, INDUCTIVE GEOLOGY.
How WE MAT OBSERVE THE FACTS, AND LEARN THEIR MEANING

STUDY I. SURFACE MATERIALS, . . 1

STUDY II. SPRINGS AND WELLS, 7

STUDY III. BOWLDERS, 12

STUDY IV. A LITTLE CHEMISTRY 18

STUDY V. QUARTZ AND FELDSPAR, 23

STUDY VI. DARK COLORED MINERALS, . 29
The Micas and lamellar species; Amphibole, Py-
roxene, Hypersthene.

STUDY VII. LIME, MAGNESIA, AND IRON MINERALS, ... 34
Calcite, Dolomite, Gypsum, Haematite, Magnetite.

STUDY VIII. REVIEW OF THE IMPORTANT MINERALS, ... 39

Table of Composition, 40

Table for Determinations, . . . .42

STUDY IX. QUARTZOSE ROCKS, ... . 44

STUDY X. MICACEOUS, AMPHIBOLIC, AND PYROXENIC ROCKS, . . 50

I. Micaceous Rocks, ..... ,50

II. Amphibolic, and Pyroxenie Rocks, . . 52

STUDY XI. PELSITIC, HYDROUS MAGNESIAN, AND ALUMINOUS ROCKS, 56

I. Felsitic Rocks, 56

II. Hydrous Magnesian Rocks, . . .58

III. Aluminous Rocks, 60

ix



x CONTENTS.

STUDY XII. CALCAREOUS ROCKS, . . . ' . .61

STUDY XIII. CARBONACEOUS, IRON ORE, AND ERUPTIVE ROCKS, . 67

I. Carbonaceous Rocks, ..... 67

II. Iron Ore Rocks, 69

III. Eruptive Rocks, . - . . . .70

STUDY XIV. RETROSPECT OF THE ROCKS, 72

Table of Rock Structure, . . . . .74
Table of Rock Composition. . . . .75
Table for Rock Determination, .... 76

STUDY XV. SEDIMENTATION, . . . . . .80

STUDY XVI. EROSIONS, . 87

STUDY XVII. STRATA, AND WHAT THEY TEACH, .... 97
STUDY XVIII. FOSSILS, AND WHAT THEY TEACH, . . .102
STUDY XIX. How THE STRATA ARE DISPOSED, . . . .108
STl'DY XX. GEOLOGICAL MAPS. . ' - , . . . . .116
STUDY XXI. GEOLOGICAL SECTIONS, . . . "~ . .123
STUDY XXII. THKRMAL WATERS, . . . . . .129

STUDY XXIII. VOLCANOES, 138

STUDY XXIV. ANCIENT LAVAS, 150

STUDY XXV. MOUNTAIN PHENOMENA. ...... 160

STUDY XXVI. MOUNTAIN FORMATION. 169

STUDY XXVII. VEINS AND ORES, ... .- . . .177

STUDY XXVIII. GEOLOGY OF SALT .186

STUDY XXIX. GEOLOGY OF PETROLEUM, 194

sTI'DY XXX. EXAMINATION OF SOME CUP CORALS, . . .202
STUDY XXXI. FURTHER EXAMINATION OF CUP CORALS, . . 210
STUDY XXXII. EXAMINATION OF SOME TABULATE CORALS, . . 218
STUDY XXXIII. EXAMINATION OF SOME BRACHIOPODS, . . 226

STUDY XXXIV. FI-RTHER EXAMINATION OF BRACHIOPODS, . 234



CONTENTS.



PART II. SYSTEMATIC STUDIES;

OR, OUTLINES OF A LOGICAL ARRANGEMENT OF THE FACTS,
WITH THE LESSONS THEY TEACH.

GENERAL DEFINITIONS AND DIVISIONS OF THE SUBJECT, . . . 245
CHAPTER I. LITHOLOGICAL GEOLOGY (Peti-oyr'tphi/), . . .248

1. Chemistry, 248

2. Mineralogy, . 248

3. Kinds of Rocks, 248

1. Physical Conditions of Rocks 248

(1) Mineral Constitution, (a) Essential Constitu-

ents. (V) Accessory Constituents, . . 248

(2) Physical Constitution, (a) Fragmental. (b) Crys-

talline, (c) Relations of Rocks to Mechanical
and Chemical Actions. .... 250

(3) Stratified and Unstratified States, . . .252

2. Methods of Studying Rocks, 253

3. Most Important Species of Rocks, . . . .254

CHAPTER II. STRUCTURAL GEOLOGY (Geognosy), . . . 255
1. General Definitions, . * 255

2. Accidents of Stratified Rocks, 256

1. Accidents of Sedimentation, ..... 256

2. Accidents of Secondary Origin, 257

3. Attitudes of Strata, 260

4. Erosion of Strata, 263

3. Conditions of Unstratified Rocks, 264

1. The Erupted Condition, 264

2. The Intrusive Condition, . . . . . .265

3. The Vein Condition, 2,65

4. Classification of Formations, 265

1. Evidences of Relative Age, 265

(1) From Superposition, . . . ... . 265

(2) Evidence from Fossils, . . . . .26(5

(3) Evidence from Intersections of Vein Matter, . 2(57

(4) Method of Combining the Observations. . . 267



x jj CONTENTS.

2. The Cycle of Sedimentation, 268

3. General Terms Employed in Classification, . . .269

4. Table of Geological Equivalents, . ... 273

CHAPTER III. DYNAMICAL GEOLOGY, . . , . . 276

1. Agency of Water, ....

1. Running Water, . . . . ... 276

2. Oceanic Action, . . . ... '. 279

(1) Ocean Currents,

(2) Wave Action, ... ... 279

3. Action of Ice, ....

4. Assortment of Marine Sediments,

2. Agency of the Atmosphere, 284

1. Wear by Wind-borne Sands, . . ' . . .284

2. Sand Dunes, . . . ' ' . .285

3. Transportation of Volcanic Ashes, . . . .286

3. Agency of Heat, . 286

1. Geological Results of Former High Temperature, . 287

(1) A Primitive Molten State, . . . .287

(2) Origin of Erupted Materials, .... 289

(3) Agency of Steam in Eruptive Action, . . 289

(4) Metamorphism Filling of Veins, ... . 289

2. Effects of the Earth's Cooling, . . , . 291

(1) Contraction and Lateral Pressure, . . . 291

(2) Evolution of Heat, . . . . .292

(3) Seismic Results of Contraction, . . , . 292

(4) Mountain Making 293

5. Geological Climates, . . 295

1. Terrestrial Causes 295

(1) Greater Heat and Greater Uniformity of Primi-

tive Climates, 295

(2) Alleged Antecedent Habitability of Northern

Regions, 295

(3) Ultimate Total Dissipation of Terrestrial Heat, . 296

(4) Ultimate Extinction of the Sun, . . .296

2. Extra-Terrestrial Causes of Climate, . . . .297

6. Tidal Action in the Earth's History, 297

1. Definitions, 297

2. Seismic Consequences of Tidal Action, . . . 298

3. Tidal Evolution of Heat, . . ... .298

4. Tidal Influence on Motions of Earth and Moon, . . 299-



CONTEXTS. Xlll

(1) Lagging of the Tide, 299

(2) Retardation of the Earth's Rotation, . . 299

(3) Diminution of Earth's Oblateness, . . .299

(4) Increase of the Moon's Distance, . . .300

5. High Primitive Marine Tides and the Consequences, . 300

6. Ingrained Meridional Trends in the Earth's Crust, . 301

g 7. Geotechtonic and Scenographic Results, . . . .302
CHAPTER IV. PROGRESS OF TERRESTRIAL LIFE, . . . .303

Definitions Fossilization Horizontal Range Vertical Range

Colonies, 303

1. Most Important Types of Plants and Animals, . . . 305

1. Plants General Classification, 305

2. Animals General Classification, . . . .306

Stem I. Protozoa. Stem II. Coelenterata. Stem
III. Echinodermata. Stem IV. Vermes. Stem V.
Mollusca. Stem VI. Arthropoda. Stem VII. Ver-
tebrata,

2. Nature of the Succession of Organic Forms, . . .314

1. The Succession a General Progress from Lower to

Higher, 315

2. Earlier Animals Generally Comprehensive, . . 316

3. The Graduation Not Complete, 317

3. The Dawn Animal, 318

4. Trilobites, 323

5. Crinoids, 324

6. Chambered Shells, 326

7. Fishes, 331

8. Reptiles, 335

9. Toothed Birds, 343

10. Mammals, 345

1. Mesozoic Mammals, 345

2. Tertiary Mammals, 348

11. Retrospect of Succession of Vertebrate Life in America, 357

12. Conspectus of Geological Range and Relative Expansion of

Principal Types of Animal Life, 359



xiv CONTENTS.

CHAPTER V. FORMATIONAL GEOLOGY, 360

1. Preliminaries. Geological Maps, 360

2. The Eozoic Great System, 361

1. How the Term is Used, 361

2. Divisions of the Great System, 362

3. Geographical Distribution and Surface Exposures, . 363

4. General Constitution of the Great System, . . 364

5. Kinds of -Rocks and Economic Products, . . .365

6. Organic Remains, . . . . ... 368

3. The Cambrian System, . . . . . . .369

1. Divisions, Subdivisions and Terms, .... 369

2. Geographical Extension, ...... 370

3. The Continent at the Beginning of the Cambrian Age, 371

4. Cambrian Rocks and Minerals, ..... 373

5. Erosion Features, . . ' 376

6. Organic Remains, . .. . . . . . 379

4. The Silurian System, , ... 381

1. Divisions, Subdivisions, and Terms, .... 381

2. Geographical Extension, 381

3. The Continent at the Beginning of Silurian Time, . 382

4. Silurian Rocks and Minerals, . . . . . 384

5. Erosion Features, 386

6. Organic Remains, . . . ' . . . . 387

5. The Devonian System, . . . . . . . 389

1. Divisions, Subdivisions, and Terms, . . . . 389

2. Distribution and Lithological Features, . . .390

3. Erosion Features, . . ... . .392

4. Organic Remains, ....... 394

6. The Lower Cartxmiferous System 395

1. Divisions, Subdivisions, and Terms, ... . 395

2. Distribution and Lithological Features, . . .396

3. Geography of the Continent during the Lower Carbon-

iferous Age . 399

4. Erosion Features, . . . . . . . 401

5. Organic Remains, . .5*' . . . . . 401

7. The Upper Carboniferous System, 402

1. Divisions, Subdivisions, and Terms. Table of Coal

Measures, ........ 402

Standard Section of the Coal Measures, ... 403



CONTENTS. XV

2. Distribution, . . 406

3. Kinds of Rocks, . . . . . . .407

4. Geological Structure, ...... 410

5. Coal Mining 413

6. Organic Remains, ....... 416

7. Origin of Mineral Coal, 421

8. Growth of the Land during the Upper Carboniferous, 422

8. The Mesozoic Great System, 424

1. Divisions, Subdivisions, and Terms, .... 424

2. The Triassic System, 424

3. The Jurassic System, 427

4. The Cretaceous System, 429

(1) Distribution and Kinds of Rocks, . . . 429

(2) Economic Products of the Cretaceous, . . 431

(3) Fossil Remains of the Cretaceous, ... 433

5. The Physiognomy of the Interior of the Continent, . 434

6. Comparative Geology of the Provinces, . . .436

7. Geological History of the Cordilleran Region, . . 437

9. The Caenozoic Great System, 441

1. Divisions, Subdivisions, and Terms, . . . .441

2. Geographical Distribution of the Tertiary, . . . 442

3. Organic Remains of the Tertiary, .... 444

4. Quaternary Materials, ...... 444

(1) Phenomena of the Surface Materials, . . 445

(2) Relation of Drift Phenomena to Climatic Causes, 446

(3) More Critical Observation of the Drift, . . 447

(4) The Terminal Moraine of the Ancient Glacier, . 448

(5) Characteristics of the Terminal Moraine, . 450

(6) Tabular Limestone Masses Imbedded in the Drift, 451

(7) Champlain Deposits, 452

(8) Quaternary Lakes 452

(9) Recent Formations, 454

(10) Organic Remains of the Quaternary, . . 456

CHAPTER VI. HISTORICAL GEOLOGY, 463

1. Presedimentary History, . . . . . . . 463

2. Inductive History, .465

1. The Eozoic JEon, 465

2. The Palseozoic^Eon, 468

(1) Movements of the Lands 468

(2) Progress of Animal Organization, . . . 469



CONTENTS.

(3) The Coal Period, 470

(4) Close of the Palaeozoic, 471

3. The Mesozoic ^Eon 472

(1) Continental History,

(2) Progress of Mesozoic Life, . . . .475

4. The Ctenozoic ^Eon, -476

(1) The Tertiary Age, . .~ 476

(2) The Glacial Epoch, . . , . .479

(3) The Champlain Epoch, . . . - . .483

(4) Effects of Glacier Pressure,

(5) The Recent Epoch, . . . . . .486



3. Ulterior History,



LIST OF TABLES.



COMPOSITION OF THE FELDSPARS,
STANDARDS OF HARDNESS, . . . .
COMPOSITION OF THE COMMON MINERALS, .
FOR DETERMINATION OF MINERALS, .

ROCK STRUCTURES,

ROCK COMPOSITION, ......

FOR ROCK DETERMINATION, ....

TYPES OF MOUNTAIN STRUCTURE,
CONSPECTUS OF THE GEOLOGY OF PETROLEUM,
STRUCTURES OF BRACHIOPODS, ....

ANALYTICAL TABLE FOR IDENTIFICATIONS, .
CYCLES OF SEDIMENTATION, ....

TABLE OF GEOLOGICAL EQUIVALENTS,

MOST IMPORTANT TYPES OF PLANTS AND ANIMALS,

FORMS OF CHAMBERED SHELLS, .

SUCCESSION OF VERTEBRATES OF NORTH AMERICA,

RANGE AND EXPANSION OF ORGANIC TYPES,

STANDARD SECTION OF COAL MEASURES,
xvii



42

40, 41

42-44

74

75

76-80
167
199
240
240
268

274, 275

305-314

329

358

359

403^105



LIST OF MAPS.



WINDINGS OF THE MISSISSIPPI, ....... 84

GEOLOGICAL MAP OF THE UNITED STATES (2 pages), . . . 118, 119

MAP OF ^ETNA AND ITS ERUPTIONS, . . . . . . 141

MAP OF HAWAII, SHOWING LAVA FLOWS, . . . . 144

GEOLOGICAL MAP OF NORTH AMERICA, ..... 361

COAL MAP OF PENNSYLVANIA AND OHIO, . . . . . 407

MAP OF TERMINAL MORAINE IN THE UNITED STATES, . . . 449

SUBMARINE CHANNEL OF THE HUDSON RIVER 455

^ONIC MAPS.

NORTH AMERICA NEAR THE CLOSE OF THE Eozoic yox. . . 371

NORTH AMERICA NEAR THE BEGINNING OF THE SILURIAN AGE, . 383
NORTH AMERICA NEAR THE BEGINNING OF THE CARBONIFEROUS AGE, 399

NORTH AMERICA NEAR THE BEGINNING OF THE COAL PERIOD, . 423

NORTH AMERICA NEAR THE BEGINNING OF THE MESOZOIC ^ON, . 439

NORTH AMERICA NEAR THE BEGINNING OF THE CRETACEOUS AGE, 440

NORTH AMERICA NEAR THE BEGINNING OF THE C^ENOZOIC Mon, . 477
xviii



SUGGESTIONS TO THE INSTRUCTOR.



1. Adhere scrupulously to the method of the book. Vary the facts,
illustrations, comments, and inferences according to opportunity or ability.

2. Do not permit any persons to thrust upon your attention, or that of
the pupils, any specimens not yet considered in the book. Most persons
have a few treasured minerals from some remote mining region upon which
you will be asked to pronounce opinions. Do not be annoyed by them. The
specimens at your door are incalculably more important.

3. Give deliberate attention to the exercises. See that every pupil learns
to elucidate every subject presented in them. Occasionally a question is
raised which even the teacher may not be prepared to solve. That is
intended. It is profitable to have something to study over.

4. If the class is small say, not over a dozen they may be ordinarily
taken into the field. This is always the best course. If the class is large,
the subject may be pursued chiefly in the class-room; but illustrations
should be abundant. In the study of minerals and rocks, a large supply of
specimens, all broken from the same bowlder, may be furnished, and one
specimen placed in the hands of each student. The teacher will then direct
attention to every character visible in the specimen, pursuing the same
method as the teacher of botany. The rock must have been previously
selected with reference to showing what is treated in the study appointed for
the day.

When this specimen is well understood, another set may be distributed,
and so on.

5. After a few exercises of this kind, individual students may be re-
quired to name such minerals in the specimen in hand as have been pre-
viously studied. Then, after the work is more advanced, a mixed lot of
specimens may be brought in, and individual students requested to deter-
mine them. Reports should be made on slips of paper, and returned with
the specimen. These may be examined immediately, if time permits, or
after the exercise. The student's report should state all the facts on which
the name of the specimen depends: Stratified or not; thick- or thin-bedded;
what essential minerals; what accessory minerals; the name. These exer-
cises should be continued for many days after the end of the subject of rocks
is reached in the book.



XX SUGGESTIONS TO THE INSTRUCTOR.

6. Get supplies of rock specimens, if the class is large, by having two
students volunteer to bring a basket full on the following day, and two others
to bring another basket full, and so on. The specimens should be preserved



Online LibraryAlexander WinchellGeological studies, or, Elements of geology, for high schools, colleges, normal, and other schools → online text (page 1 of 40)