Ralph S. (Ralph Stockman) Tarr.

A laboratory manual for physical and commercial geography online

. (page 4 of 16)
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As the lichens grow, how do they aid in rock disintegration?

. Are there any bushes or

trees sending their roots down into the rock ? What effect will the

growth of these roots have on the rock?

Solution. As the rain water passes through the soil it takes with it certain substances (like

carbon dioxide and humic acids) supplied by plant decay. The water then has power to
dissolve some minerals. Where, in this rock outcrop, will water percolate most freely?

If it flows along a joint plane, what effect will it have on the rock on either side?

If it slowly percolates between the mineral grains, what effect will it have on them?

State how the work of solution aids rocks in crumbling.


Have you ever seen an iron spring, or a sulphur spring, or other kind of mineral spring?

Why are such springs called mineral springs ?

How did the water obtain its load of dis-
solved mineral ?

"Hard water" is water with mineral matter in solution. How did this get in solution?

Decay of Percolating water not only dissolves some minerals, but it causes some to change greatly,

rocks. as i ron i s caused to change to rust. Break off a piece of the rock to see whether any of the

minerals show such a change. Describe the difference between the outer and inner parts of

the piece of rock.

Are any of the minerals rusted red or yellow on the outside? Are

any of them changed to dull whitish color? If one kind of a min-
eral in a rock decays, and the other does not, how does that weaken the rock as a whole?

State briefly how decay results in rock disintegration.


Make a list of the agencies of weathering that yon have observed at this outcrop.

Add to the list any other agencies of weathering that you know about, but have not observed.

What As the rock of this outcrop disintegrates, what becomes of the fragments?

of the dis-

Do any fall

to the base of the cliff, forming a talus? Describe the talus and ex-
plain its formation.

Are any of the fragments carried off by streams?

Are any taken away by plants ? How ?

What becomes of the dissolved


Make a brief statement to show what becomes of the products of rock weathering.


The forma- If the slope of the bedrock is so gentle that the products of weathering are not all

tion of soil, removed, a mantle of soil is formed, called a residual soil. How would such a soil differ in

character from the surface to the bedrock?


How would the roots of plants aid in making the soil finer ?

What effect would earthworms have on the texture of the soil?

Why would a residual soil

be different on different kinds of rocks, such as limestone, slate, and granite ?

Would a resid-
ual soil grade into the bedrock, or would there be a sharp line separating them?

., What is the

nature of the soil on this outcrop? Describe it.

Is it a residual soil ?


Other ob- Write down any other observations you have made on this excursion, or any other facts

servations. y Qu k ave leaded, if y 0U have ever noted the effect of weathering elsewhere, as on bowlders,
or on stone buildings, or on the headstones in cemeteries, state what you have observed.




Purpose. To study the work of streams in eroding their valleys and forming deposits.

Introduc- The banks of a comparatively small stream whose current is alternately swift and slug-

tory. gi s h will best serve the purpose of this excursion. Any water course will, however, give an

opportunity for profitable work, even though some of the observations outlined cannot be made.

Failing a perennial stream, the course of a wet-weather stream along a roadside or elsewhere

will afford many illustrations of stream processes.

Transpor- Is the water clear or cloudy? If it is

tation of

sediment. not c ] earj w hat causes the cloudiness?


.__ How are clay and other fine earthy particles carried

along by the current?

What is the nature of the bottom of the channel at this point?

Was the material of which it is composed brought by the current? If so,

was the current faster or slower at the time when the material was deposited ?

How do you know this ?

If the stream is flowing over bedrock, what does this fact indicate as to the transporting
power of the stream at this point?


Examine, if possible, a place in the stream course where the water is shallow and flowing
rapidly. What kind (as to size and nature) of particles are being rolled along on the bottom?

Throw pebbles, sand, and clay into the current to see how coarse material can be transported.

Would larger or smaller particles be moved at flood times ?

What evidence of this is afforded by the bowlders and pebbles in the bed of the stream at
different points in its course ?

When may they be moved again ?

Erosional Have the bowlders and pebbles in the stream bed rounded or sharp corners ?

work of

streams. Why?

What does this indicate as to the way in which the material of a bowlder or pebble will
eventually reach the sea?


What will be the effect on the bedrock as the pebbles and bowlders are rolled over it ?

What effect will the transportation of sand particles have ?

What will be the effect, in both cases, on the depth of the stream channel ?

What is the source of the material which the stream carries '/

How does weathering assist the stream in securing this material ?

How are stream valleys deepened ?

Is the course of the stream a straight line ?
What is meant by a meandering course ?


What work is the current doing where it swings toward the bank in a meander curve?

What effect will this have on the width of its channel ?

How does weathering aid in the widening of stream channels ?

What illustrations of this do you find here ?

Why have ripraps and embankments been built by man along many streams ?

Deposition Where are bars formed in the stream's course ?

of sedi-

. .Of what materials are they composed ?


How do you account for their presence and composition in each case noted ?

When will this material be moved again ?

Where will it ultimately be deposited ?

Is sediment carried in one continuous journey from its starting place to the sea?
Describe the process.

What forms may the material take when deposited in the sea or a lake ?

What illustrations of

this do you find in the small pools or ponds in the stream course?





Write a short paragraph summarizing the work of streams in deepening and widening
their valleys and in forming sedimentary deposits.



Purpose. To study the waves and currents on a coast line; to note their importance in erosion, trans-

portation, and deposition; and to study some of the land forms resulting from their action.

Introduc- Even the shore of a very small pond will often illustrate the main phenomena which it is

tor y- the purpose of this excursion to study ; therefore, if a large lake or a sea coast are not access-

ible, this excursion may nevertheless be undertaken with profit.

The wave. Are there any waves on the water surface ? About how high are they ?

What is the cause of the waves?

At what time are the waves higher than now?

As the waves approach the coast, how do they change in form '

Are there points where the waves reach the coast with greater vigor than others ?
What reason can you give for their greater vigor in such places?

Currents. Is there a tide on this coast ? If so, describe it.

Does the tide cause currents in any place? When the wind blows steadily

over a body of water, what other movement of the water is there besides that of the waves?


Is a wind-formed current a rapid or a slow movement ?

How does such a current compare in power Avith the waves ?

Can it transport coarse sediment? Clay? •_

Wave work Do the waves beat against a headland at any point on this coast ?
on head-
lands. j g ^ headland hard rock or unconsolidated material ?

Is it steep or gently sloping? What evidence

is there that the waves are working to erode the headland?

How does weathering assist in the work?

If this work of erosion continues, what change will take place in the form and position of the
headland? 1

Is such work most rapid in consolidated or in unconsolidated material?

As weathering and wave erosion remove material,

what becomes of the fragments?

Wave work Of what is the beach made?

on beaches.

As the waves wash up on the beach, what size

material — clay, sand, or pebbles — do they move?

What size material can the waves move in times of storm? .


What relation, if any, is there between the beach material and the headlands ?

How was the beach material brought to its present position ?

As the waves move the beach material about, what change in size of particles results?

Where are the finer particles, such as clay, carried?

How do the wind-formed currents aid in this


The undertow?

How does such transportation aid in explaining the absence of clay beaches?

In explaining the frequency of clay deposits in protected bays where currents enter?
In explaining the fact that clay often covers the bottom at a short distance from the beach?

Animal and Are there any animals or plants living in the zone reached by the waves ?

plant life.

What kinds?

Do they aid or retard the work of the waves or currents in any way ?

^|ther What other phenomena are illustrated on this coast ?



Does ice, for instance, ever form here; and what effect does it have?

Is the coast line a place of rapid or slow change?

Are there ripple marks? Study their formation and explain them.

State any observations you may make on the work of the wind in drifting sand about.

What observations have you ever made on other coasts than this one ?


Form of the Is the coastline straight or irregular? Is it a raised or a lowered coast?


Have the waves and currents produced much

or little change on this coast?

Are they now causing much or little change ?

Briefly describe the coast as you have observed it; state how the agencies of denudation
are modifying it, and explain its present form so far as the facts you have seen enable you to

do so.





Method of





For Each Student. — Fragments of quartz crystal, feldspar, hornblende, halite (salt),
biotite mica, calcite, gypsum. Steel knife or scratch point. Window glass (fragment).

For General Class Use. — Dilute hydrochloric acid, and several glass stirring rods ; or
acid- dropping bottles.

To learn the properties by means of which the more common minerals may be identified and

A mineral may be defined (in general terms) as any inorganic solid, formed in nature,
which is composed of certain elements in definite combinations. The nature of the elements,
the amounts of each present, and the way they are combined give each mineral its own pecu-
liar characteristics. Thus a mineral is a naturally formed solid which has the same composi-
tion and structure throughout its mass.

Number your specimens from 1 to 7. Then make the observations as directed below
and record the results. Refer to each specimen by the number you have given it.

Which specimens are light colored?

Which are dark? What is the color of No. 1?

Of No. 2? No. 3?

No. 4? No. 5? No. 6?

No. 7?

If one mineral scratches another, which is the harder, the one scratched or the one used
to scratch with?

Number of

Numbers of Specimens
which it scratches

Numbers of Specimens
which scratch it

By using a sharp point or corner of each
specimen to scratch with, and selecting a flat
place to scratch on, try to scratch each mineral
with every other one and set down your ob-
servations in the table opposite. Be careful
not to press so hard as to break off the points
by mere weight.


Cleavage ;
and crystal-
line or


tions on
faces and

Which of the seven is the hardest specimen? Which is the softest?

Arrange the specimens in the order of their hardness, putting the hardest



Next Hardest

Third Hardest

Fourth Hardest

Fifth Hardest

Sixth Hardest

Softest '

Which numbers can you scratch with your finger nail?
Which with a piece of steel or glass?

Many minerals break more readily in certain directions than in others, thus giving these
minerals the property of cleavage. The smooth planes along which these breaks occur are
called cleavage planes. In other directions the mineral breaks with a rough or uneven surface.

Not all smooth faces seen in minerals are cleavage planes. If a mineral is built up under
proper conditions, and is free to grow in all directions, it takes a definite form known as its
crystal form. Such minerals have smooth outside faces, called crystal faces.

Cleavage planes and crystal faces can be distinguished by the fact that cleavage planes
repeat themselves, one parallel to the other, while crystal faces simply bound the outside of
the crystal.

If the proper conditions are not present when a mineral is forming, it will not become a
crystal but will appear as a lump of the substance without definite form. Such a mineral is
said to be amorphous, a word meaning "without form." Minerals in the amorphous state
have neither crystal faces nor cleavage planes.

Minerals are either crystalline or amorphous. Complete crystals of minerals have smooth
crystal faces. Parts of crystals may or may not show smooth cleavage planes. The presence
of a cleavage plane indicates that the mineral will split in that direction, with a- smooth face,
as finely as it can be divided. Not all crystalline minerals have cleavage planes, while some
have them in a number of directions. Amorphous minerals have no smooth faces.

Which of your specimens have crystal faces or crystal form ?

Which have cleavage planes?

Which have cleavage planes in more than one direction?

How many of them have cleavages at right angles to

each other? How many at inclined angles

to each other? Which of your specimens

are amorphous?

Suggested Growing crystals. — Dissolve as much salt as possible in a glass of hot water. Suspend a cotton string
home work so that its free end will extend below the surface of the solution. Allow the solution to cool as slowly as
for stu-
dents, possible. Note the results.


Try this also with a solution of sugar. Of alum. Is there any difference in the form of the crystals ?
Try the effect of cooling a salt solution rapidly.

Make a cold solution of either

sugar or alum and allow it to evaporate slowly. Why should these crystals be so much larger and more

perfect than the others ?

Luster. The manner in which light is reflected from a mineral gives it an appearance that is

termed its luster. Thus from some minerals the light is reflected so that it appears like a
glassy surface. Such a mineral is said to have a glassy luster. Others have pearly, metallic,
oily, earthy, etc., lusters. Describe in these terms the luster of each of your specimens, and
set down in the table.

Acid test.



Name of Specimen*










Have the teacher tell you the name of each of your specimens and set it down in the third
column above, opposite its number.

Apply a drop of acid to each of your specimens. If any of them begin to bubble, you
have a chemical reaction ; that is, the mineral is changed by the acid. Which of the

minerals shows such a reaction ?



Materials. For Each Student. — Specimens of quartz, orthoclase feldspar, plagioclase feldspar, muscovite

mica, biotite mica, hornblende, iron pyrites or pyrite, calcite, dolomite. Steel scratcher.

For General Class Use. — If possible have large crystal specimens of the different minerals
named above for examination by the class. Hydrochloric acid and stirring rods.

Purpose. To learn the properties of the common rock-forming minerals.

Introduc- On the following page is a table with a column for each specimen named above. Deter-

tor y« mine the characteristics of each mineral and set down your observations in the proper place,

as indicated. The chemical composition of each is given by its chemical symbol and is also
(in general terms) written out. The teacher will describe those elements mentioned with
which you are not familiar. These minerals are the ones which make up the bulk of the
rock masses of the earth. Hardness is to be stated in terms of harder than steel, harder than
a finger nail, softer than a finger nail.

How many of the minerals have oxygen? How many have

silicon ? What does this indicate as to the abundance of these

elements in the earth's crust?

How many different elements are present in all the min-
erals in your list ?











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Method and


For Each Student. — Specimens of hematite, magnetite, halite, gypsum. Steel scratcher.

For General Class Use. — If possible, some specimens of limonite, magnetite, gold, silver, copper,
lead, and zinc ores. (In some localities the teacher may find it desirable to have these minerals for
each student.) Hydrochloric acid and glass stirring rods. .

To learn the characteristics of a few important economic minerals.

Make observations and describe each of the above minerals ; putting the description of
results. each in the form of a sentence, as below.

Hematite (Fe and 0) has a color ; a hardness

; crystal faces are

(or are not) present; cleavage planes are (or are

not) present; these are at angles to each other ;

its luster is ; and it does (or does not) respond to the acid test. It

is used as a source of

Magnetite (FeO)

Halite (NaCl) (CI = Chlorine)


Gypsum (CaSO< + H 2 0)

Examine the specimens (if any) which the teacher distributes and set down the most striking
characteristic of each.



Materials. For Each Student. — The specimens of the rock-forming and economic minerals previously


Purpose. To learn to distinguish between minerals having simUar properties.

Refer to the table of properties you have already made, and reexamine the specimens.

Comparison In what characteristics do quartz and feldspar resemble each other?

of minerals.

, How can they be

told apart ?

Examine the cleavage faces of the orthoclase and the plagioclase

feldspar. Which kind has the fine parallel lines ? i .

How do the two micas differ in color ?

Would the fact that iron is present in the biotite sug-
gest any explanation for this ?

In what properties does hornblende resemble the feldspars?

In which does it differ ?

Is its cleavage as easy to see as that of the feldspars?.

How may hornblende and mica be distinguished?

How would you most quickly recognize pyrite ?

. What resemblances have calcite and dolomite?


How may they be distinguished from each other ?

In what ways does halite resemble quartz?

Taste both. What is the result?

What would happen to halite if it were present near the

surface of the earth in a humid climate ?

How could you most readily identify hematite ?

What is the most noticeable property of

gypsum? _






For Each Student. — Specimen of granite, sandstone, fossiliferous limestone, schist. Fine-
pointed steel scratcher, or knife point.

For General Class Use. — Hydrochloric acid and glass stirring rods.

To learn the cfiaracteristics of the four great classes of rocks.

Examine your specimen of granite. Of how many different minerals is it composed ?

Are the minerals crystalline or amorphous ?

Identify each mineral, and make a list of them in the order of importance as to amount present.

How are the minerals arranged with respect to one another ?

This kind of rock is known as an Igneous (= Fire) Bock because of the fact that it is formed by the
cooling of a hot molten mass of rock magma which rises from within the earth. If such a molten mass cools
slowly, the minerals can separate out into crystal grains of good size, as in the granite you have examined ; if
they cool very quickly, the rock which results is like a black glass, or furnace slag. There are all gradations
between these two extremes. Then again, the molten magmas are of different composition ; some have
elements that others lack. Consequently, minerals that are present in one igneous rock may be absent in others.

tary rocks.

What mineral composes the bulk of your sandstone specimen?

Are other minerals visible? If so, what proportion of the mass do they

form ?

Eub your finger (or a knife) with some pressure over the surface of the specimen. What is the
shape of the particles you break off?

What differences do you see between the sandstone

and the granite ?


Sandstone is a Sedimentary Bock ; that is, it is one of the great class of rocks which are formed by
deposition, generally in water. The material, or sediment, of which they are composed, is usually brought by
streams which have gathered it along their courses and carried it in their currents to their mouths, where they
must deposit it, because the current ceases. Sedimentary rocks are all alike in the fact that they have been
formed by deposit from a current, usually a water current ; but wind, for example, may also act as a carrier
and depositor of sediment.

Organic What traces of animal life does your limestone specimen show ?


Where do such animals


What becomes of their shells when they die ?

Does the acid affect this rock? How might such a rock be formed?

Limestone such as this is an Organic Bock. Organic limestones, however, grade into those which have
formed chemically (as a deposit of salt would form in a glass if you dried up a salt solution) . When limestones
are chemically formed, they are generally classed with the sedimentary rocks.

Metamor- Of what minerals is your schist specimen composed?

phic rocks.

How are these arranged?

How does this affect the rock's strength?

Why is it not as strong as a granite?.


Along the lines of what mineral does it break most readily ?
. Why?

Schist is one of the great class of Metamorphic (changed) Bocks. Originally they were igneous, sedi-
mentary, or organic rocks ; but later they were heated and compressed in the earth's crust, so that they have
acquired altogether different characteristics than they had originally. Such a change in rocks is called

Does solid rock appear at the surface anywhere near your home? To

which of these four classes of rocks does it belong ?

At the next period bring a specimen from the rock outcrop.




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Online LibraryRalph S. (Ralph Stockman) TarrA laboratory manual for physical and commercial geography → online text (page 4 of 16)