Ralph S. (Ralph Stockman) Tarr.

A laboratory manual for physical and commercial geography online

. (page 6 of 16)
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Fig. 17.

the inter-
on cross-

so that the folded edge rests on the line A-B, leaving this line visible. At A and B draw short
(£") vertical lines down from the folded edge of the paper, and mark A and B, respectively, at
their ends. A and B are each at sea level, or elevation. With sharp pencil mark on the
folded sheet (with similar short vertical lines) the exact point of intersection of each contour
line with the folded edge. Begin at A and continue to B. Below each vertical line indicate
by a figure the elevation of the contour line whose intersection it marks. When this operation
is partly completed, the edge of your folded sheet should be similar to Fig. 17.

On the accompanying cross-section paper (Fig. 18) draw a pencil line along one of the
lower horizontal ruled lines, so that it stands out distinctly from the rest. This is to be your
line or sea-level, or base-level line. At the left-hand end of the zero line, draw a line per-
pendicular to it, and 13 small squares high. Number the horizontal lines which this perpen-




| 1
1" 2"

JJ'e"! H" i." J" 6"i„ ^ NOT COMPLETED



Fig. 19. — To illustrate Method of making Cross Section from Contour Map.


dicular crosses, from 1" to 13"; the 1" line being the one next above the zero or sea-level line.
Mark this end of the drawing A.

Now lay the folded edge of the sheet, on which you have marked the intersections of the
contours along the sea-level line, so that the point A on the folded edge coincides with the
point A on the horizontal line of the cross-section paper. Next make a dot with your pencil
on the 1" horizontal line of the cross-section paper, at a point exactly above the place where
you have marked the intersection of the 1" contour line on the folded edge. For. the 2" con-
tour intersection put a dot on the 2" horizontal line; and so on until you have put dots on the
proper horizontal lines for all the contour intersections, and have reached sea level again at B.
Next connect the dots by means of a smooth curved line, avoiding sharp angles. When
partly drawn, your cross section should be similar to Fig. 19.
Horizontal The scale of the map was 1 inch = l foot. Therefore the horizontal scale of your cross

and vertical section is the same, and you should print or write this below your cross section, thus : Hori-

zontal Scale 1 inch = 1 foot. What is the vertical scale of your cross section?

Above the cross section, write "Cross Section, along the line A-B

on Map, Fig. 15." Always mark the vertical and horizontal scale, and the line along which
it is taken, on every cross section you make.


1 1 1 _ 1 , I i 1 —J __- . ( 1 1 1 1 1 1 . ' 1 ' 1 —

. . 1 , , ___ ___ _ .

i l—J 1 . i 1 , 1 1 1 I 1 — 1 '

— — — ■ — I. i ■ — — — | — i i — — — i — i i i i j , i L_J , , __ i

— __ , , __ .

»' — I — ' — • — ' — ' ' ' 1 — • 1 — < — i 1 • — ' 1 1 — 1 — . 1 — i — 1 — I — i — i , i - , i i ;
:____: zzEffi






(showing heights above (showing height above

mean sea level instru- sea < horizontal form,

mentally determined) and steevness of slope


of the surface)


Falls and


Mine dumps



Canals and


Sand and
sand dunes




Lake or




Salt marsh Fresh marsh




= — ii it i fin


I I I I I I *=*=

Tidal flat

City or

Roads and Private or

buildings secondary road



Electric railroad
in roadway




v ~— ««>




U.S.township and State line
section lines

County line Civil township



Bench mark

Church or

Coke ovens

Oil wells

Mine or




and jetties





Land-grant City.village,or Park or

line borough line cemetery line


U.S. mineral

$, LS



Mine tunnel Mine tunnel Light-ship

(showing direction) (direction unknown)



Fig. 20. — Conventional Signs used on Atlas Sheets of the United States Geological Survey's Topographic Maps.



Materials. For Each Student. — Ruler. Pencil. Several sheets of plain paper. Montross sheet. Maryland-


Purpose. To teach the understanding of the conventional signs used on a topographic map, and the

making of cross sections and profiles from such maps.

Conven- Figure 20 illustrates the conventional signs used on the United States Geological Survey

tions of a

topographic topographic maps. What color is used for contour lines? > What is


meant by Relief?

What color is used for road, county, and state lines, and for buildings and cities ?

Why should these features be called cultural features?

What color is used to indicate water ?

Cross sec- Make a cross section (on accompanying sheet of cross-section paper) of part of the

tionofa Montross sheet along a line between Stony Hill and Montross, proceeding as you did in
topographic making the cross section of the simple contour map in the preceding exercise. A very sharp
ma P- pencil and even greater care will be necessary. In making the cross section note carefully

whether you are crossing a valley or a divide between valleys.

Exaggera- What is the horizontal scale of the map ?

tion of

relief in a What is the contour interval? '_ What is the vertical scale of your


sec ion. cross section ? If the horizontal scale of your

cross section is one inch = one mile, and your vertical scale is \ inch = 20 feet, how much is

your vertical scale exaggerated? (5280 feet = l

mile, therefore 5280 feet = linch horizontal scale. 8 x20 = 160 feet, therefore 160 feet = 1 inch
vertical scale. Therefore in the cross section 160 feet vertical scale equals 5280 feet in
the horizontal scale.)

Why would it have been much better to use a vertical scale \ inch = 80 feet ? ....


Plot the same cross section on this scale. What is the exaggeration of the vertical scale in


this case ? Always endeavor to avoid too great

exaggerations of the vertical scale in making cross sections and profiles.
Profile of On the map locate the main stream, which occupies the valley between Chilton and

a stream Stratford, and is crossed by the road which connects these villages. Trace this stream from
va ey ' its source to the point where it flows into the lake.

How many contour lines does the main stream cross in that distance?

How many feet, therefore, does it descend? In about how many

miles ?

Make a profile of this valley between its source and its entrance into the lake. The method
is the same as for making a cross section, except as follows : Start at the left-hand end of
the folded paper in marking the intersections of the contours. As often as the stream bends
appreciably, swing your folded edge of paper so that it is continually parallel to the stream's
course. Be careful to keep the pivot point on the map and on the folded edge of the paper
identical when swinging the paper to a new direction. Plot the results on the cross-section
paper, using this time a vertical scale of \" = 40 feet.

Where is the stream's profile steepest?

In what portion of its course is it most gentle?

What is its average descent per mile near its source ?

In the middle of its course?

What information regarding a region can be gained at a glance from a cross section ?

Of what practical use would a profile of two possible roads, that he might follow, be to a
farmer intending to haul grain to town ?




Materials. For General Class Use. — Tank and land model. Spray, nozzle, and hose. (The nozzle should be

of the kind used in spraying trees for insects.) Water under pressure.

Purpose. To study some of the erosional and depositional processes of nature by actual observation of

their progress in miniature.

The land This land form is supposed to have been newly uplifted from beneath the sea, and no

form. rain has as yet fallen upon it. It is composed of alternate layers of sediment, formed of

different kinds of material.

With reference to the compass directions, describe the topography of the land form.

Where is it hilly?

Where has it plains?

Are there any mountain ranges ?

Are there plateaus ? Any isolated peaks?

what material is the surface layer composed?


Character- Turn the spray upon the land surface. Have it of sufficient volume to develop streams,

istics of a b u fc avoid having the drops of water too coarse. This spraying is to simulate, as nearly as

young land poggikig the rainfall of nature,

surface. r

What determines the courses of the streams as they flow at first? ,

. Why are such

streams called consequent streams?

Do any lakes form ? What is the

origin of their basins?

Are the divide areas between the stream courses flat or ridgelike ?

What age condition of a land surface does the presence of consequent

streams, lakes, and flat-topped divides indicate?

Examine the stream currents carefully. Are they carrying sediment ?


Transpor- If so, where do they get it?

tation and



Are they carrying sand particles? How are

the sand particles moved along?

How much larger stream do you think would be required

to move a pebble as big as your fist? How

are clay particles carried along? ,

Can you tell whether the streams are carrying any material

in solution?

As the currents transport the sand and clay particles, what is the effect on the stream


Where are they deepened most?

What is meant by headwater erosion?

Do the main streams follow straight courses ? What causes them to meander ?

What is the effect of this meandering on the width of their valleys ? ..
What is meant by lateral cutting of a stream?

By undercutting f ..


What is the shape of the cross section of the stream valleys as they are first cut ?
How is this "gorge-form " cross section changed by the lateral cutting?

Do tributary streams first deepen their valleys near their sources or at their junction

with the main valleys? How do you explain

this? 1

What effect has the development of tributary valleys on the flat-topped divides?

Waterfalls. Have any waterfalls developed in the stream valleys? What is their


Why does a deep pool form beneath them ?

Why do the waterfalls not remain stationary in position ?

In which direction do their crests move ?

Deposi- Are the sand particles, which the currents are rolling along, carried uninterruptedly to the


processes. still water at the mouths of the main streams ? Where do they lodge ?

What do they form? Are river bars permanent?


What is the effect of the formation of a bar on the course of a stream?

What large river do

you know of which has many sandbars?

Why are these dangerous to navigation ?

Which can carry the most sediment, a slow current or a fast one?

Where are currents fastest, on steep or on gentle slopes ?

If a stream has much sediment in the upper, steep part of its

course, what becomes ' of this sediment when the stream flows over a gentler slope ?

Examine the streams on the land form to find

such a condition. What kind of a topographic feature results?

Describe and make a small sketch of an alluvial fan.

Watch the stream course as it flows over the alluvial fan ; why does it shift its position ?

Does the building up of the alluvial fan make the slope of the stream steeper or more gentle
at this point? What is the grade of a stream ?


What becomes of the sediment that the stream carries when it enters the still water ?

Where are the sand particles deposited?

Where are the clay particles deposited?

Which kind of deposit, sand or clay, covers

the larger area of the bottom of the still-water basin?

What topographic form do the sand particles build up as they are deposited in the still

water? Is the slope of the top of the delta steep or gentle?

How does the delta compare and contrast with the alluvial fan in

outline and slopes? .




Types of
land forms.

Factors in
the devel-
opment of
land forms.

of the

To teach the simple origin of land forms, and the factors which give them complexity.

Note: — This section should be carefully studied before going on with the study of the land in its topo-
graphic and cultural relations.

Most land forms are the result of the processes of denudation operating on the rocks
of the earth's crust.

The nature and configuration of these forms are dependent primarily and fundamentally
on the position and structure of the rocks. There are two fundamental types occupying large
areas : —

1. The Plain-plateau Type: The rocks are in horizontal or nearly horizontal beds.

2. The True-mountain Type : The rocks are folded, faulted, and tilted, or are massive
crystalline rocks.

Most lesser land forms are resultant upon variations in the conditions and nature of the
denudation of these simple, original forms.

The following factors condition the variation : —

(a) The nature of the rock, whether consolidated, or unconsolidated, or partly consolidated.

(6) The length of time that the region has been exposed to denudation.

(c) The elevation of the region above sea level, and its distance from the sea.

(d) The climate, — whether humid or arid.

(e) Accidents which have interfered with the normal development of the region. Glaci-
ation and volcanic disturbances, for example, may be considered as such accidents.

With a knowledge of the primary type, whether Plain-plateau or True-mountain, and a
consideration of the degree to which the five factors enumerated above have been operative,
we can interpret most land forms. Or, by a consideration of the land forms, we can appreciate
the factors which determine their present condition.

That part of North America which comprises the United States is capable of being divided
into a comparatively small number of areas, each of which constitutes a physiographic unit, or
province. Moreover, these units bear a most interesting physiographic relation to each other ;
and, taken collectively, they illustrate practically the whole science of the physical geography
of the land. Again, in each of these physiographic provinces the United States Geological
Survey has made very fine contour maps, and from these may be chosen one or more which
are typical of the province.

The United States, therefore, offers to the American student an excellent opportunity to
become acquainted with the science of physical geography of the land in some of its most in-
teresting phases, and to gain a knowledge of the physiographic provinces, and the influence
their topography and structure have had on the development of the land, its present industries,
and its future possibilities.

The following sections constitute such a study of the regions of the United States. The
studies go from the simple to the complex, and, when they are completed, the student should
have a comprehensive knowledge of the location of the broader physiographic divisions of the
country ; and an understanding of the topographic, climatic, and cultural relations of each.




I "•

1 1










^3 2
J ft,


+ + +•




e 1





Extent of
the Glacial-
Lake areas.

For Each Student. — United States Geological Survey Map of the United States (size 18x28
inches) with contours. Fargo sheet, North Dakota-Minnesota. Colored pencils.

To study a very young plain and the influence it exerts on human habitation and industrial

When the Continental Glacier of the Glacial Period was receding, after the last (or Wis-
consin) advance of the ice (Text-book, Chapter VIII), and had melted back to points near the
northern boundary line of the United States, there were times when the ice front remained
stationary for a considerable interval. During this long period of recession the ice mass
dammed up the north-flowing rivers (for example, the Red River of the North), and their
waters spread out and formed huge lakes. (See Text-book, pp. 78 and 149.) Into these lakes
much sediment was poured by the streams from the glacier and from the land, and this sedi-
ment was deposited on the lake bottom. Finally, after the glacier had melted away com-
pletely, the lake waters drained off and the bottoms of the lakes became dry land.

Figure 21 is a diagram map of the United States on which have been outlined the
different physiographic regions studied in this and succeeding sections. The areas which are
marked " G. L. P." on the map were formerly bottoms of glacial lakes. Plot the outlines of
these Glacial-Lake Plains on your contour map of the United States. Latitude and longitude,
the position of state boundary lines, and the location of cities offer the best aids in locating
the outline. Extend the Glacial-Lake Agassiz outlines into Canada.

Examine the areas as you have outlined them on your map of the United States. About
what proportion of the area of the United States was once covered by glacial lakes ?

What two places along the outlines seem to

have been outlets to these lakes?

What is the highest contour bordering each of these out-

flow channels ?

Why was there an island in the Glacial-Lake Agassiz ?

With green pencil, color in lightly

(on your contour map of the United States) the regions of the Glacial-Lake Plains. Fill in
(with green also) a square for a legend, as indicated on the outline map. Label this square

Study of a « Glacial-Lake Plains."

of the Gla- Examine the Fargo (N. D.) sheet. What is the most northern degree of latitude shown ?


Plains. The most southern? Between what


degrees of longitude is the area included?

Locate this area on your United States map and outline it with ink. Letter or write in the
name of the sheet beside the rectangle you have drawn. How much larger is the horizontal

scale of the topographic map than that of the United States map ?

What is the contour interval of the topographic sheet ?

A typical Make a cross section between the S of Sabin and the H of Horace, using the same hori-

cross sec- zontal scale as that of the map, and allowing one vertical division of the cross-section paper

tion. £ or everv 20 feet of elevation. On each cross section you make always mark the name of the

sheet, the points between which it is taken, the horizontal scale, and the vertical scale adopted.

What, in general, is the nature of this land surface, as shown by the distance apart of the

contour lines and the cross section you have made?

What is the shape of • the stream

valleys as shown by your cross section ?

How deep are they ?

How wide?

Are this

shape and size characteristic of an old or young valley?

What is the nature of the divides between the stream

valleys ? Why would rain water run off

very slowly from this region? In which

direction do the main streams flow? ;._ What

is the difference in elevation between the highest and lowest points on the map ?

Where is the highest point ?

The lowest point ?

What are the directions of the wagon roads in this region ?

What is their pattern, or

arrangement ? Why is it possible for the

railroads to have such straight courses?

What kind of deposits are laid down in still water, fine or coarse grained?

What two reasons can you give why this should be a fine agricultural region?


Why are many farmers now crossing into Canada to the region north of this part of the
United States?

Count the number of houses in ten adjoining squares. Allowing

five people to each house, what is the average population per square mile in this section ?

What is the position of the houses with

respect to the roads ? '

Write a short paragraph, below, explaining why the deposit of sediment over a lake
bottom would, on the disappearance of the lake waters, give a region of this nature, and tell
why such a region encourages agricultural industry.



Materials. For Each Student.— Geological survey map of the United States, used in preceding exercise.

Donaldsonville (La.) sheet. Colored pencils.

For General Class Use. — Chart No. 14. Mississippi River Commission. The Fargo (N. D.) sheet.

Purpose. To study a very young plain in process of formation by liver deposit; and the conditions affect-

ing human occupation of this plain.


Extent of
the Missis-
sippi Flood-
plain and
Delta area.

The Mississippi River, in its lower course, carries enormous amounts of sediment in its
waters. In places it deposits some of this sediment, in others it secures more. At its mouth
it deposits all its load. The flood plain and delta of the Mississippi are built up of such sedi-
ment deposits, and the river is continually modifying the flood plain, and extending the delta.
(See Text-book, pp. 61-66, 325-328.)

On your contour map of the United States plot the outline of the area marked M. Fl. P.
and D. on Fig. 21. About what proportion of the area of the United States does the Missis-
sippi Flood-plain and Delta region constitute? What is the approximate

length of this area in miles? 1 What is its

average width? What is the pattern of the

smaller streams on the flood plain and delta?

Study of
"No. 14.

Are they many or few as compared to adjoining regions ?

At the mouth of the Ohio River the altitude of the Mississippi River is 294 feet above the sea.
The distance from the mouth of the Ohio to the mouth (head of passes) of the Mississippi is
1060 miles. What is the average descent (in feet per mile) of the Mississippi between the

mouth of the Ohio and its mouth at the Gulf of Mexico ?

With blue pencil, color in lightly on your contour map of the United States the area of
the Mississippi Flood-plain and Delta region. Fill in (with blue pencil also) a legend square,
as indicated on the outline map (Fig. 21).

What is the scale of this chart?

What is the nature of the river's course as shown on this chart?


How long are the river bends?

. On which side of the bends is the river depositing material?

Do these bars have a constant shape and position ? (See red lines and legend explaining them.)

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Online LibraryRalph S. (Ralph Stockman) TarrA laboratory manual for physical and commercial geography → online text (page 6 of 16)