Google
This is a digital copy of a book that was preserved for generations on Hbrary shelves before it was carefully scanned by Google as part of a project
to make the world's books discoverable online.
It has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject
to copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books
are our gateways to the past, representing a wealth of history, culture and knowledge that's often difficult to discover.
Marks, notations and other maiginalia present in the original volume will appear in this file - a reminder of this book's long journey from the
publisher to a library and finally to you.
Usage guidelines
Google is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the
public and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing this resource, we liave taken steps to
prevent abuse by commercial parties, including placing technical restrictions on automated querying.
We also ask that you:
+ Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for
personal, non-commercial purposes.
+ Refrain fivm automated querying Do not send automated queries of any sort to Google's system: If you are conducting research on machine
translation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the
use of public domain materials for these purposes and may be able to help.
+ Maintain attributionTht GoogXt "watermark" you see on each file is essential for informing people about this project and helping them find
additional materials through Google Book Search. Please do not remove it.
+ Keep it legal Whatever your use, remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just
because we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other
countries. Whether a book is still in copyright varies from country to country, and we can't offer guidance on whether any specific use of
any specific book is allowed. Please do not assume that a book's appearance in Google Book Search means it can be used in any manner
anywhere in the world. Copyright infringement liabili^ can be quite severe.
About Google Book Search
Google's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers
discover the world's books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web
at |http : //books . google . com/|
'n_, V- .
»--*^"^T^'^v,w^^
',<':■
/I
&^
DEPARTlCEirr OF THE IKTEHIOE-H. 8. a^OLOGIOAL BDRTEY
J. W. POWELL, UlRECTOR
'^
yyt-^
ORIGIN AND NATURE OF SOILS
NATHANIEL SOUTHSATeIsHALER Y
EXTRACT FROM THB IWELFTH 4KNOAL REPORT OF THB PtRBCTOR, 1S90-'91
WASniNGTOy
OOVEUNMBNT PBINTINQ OFFICE
1892
.r
THE ORIGIN AND NATURE OF SOILS.
BY
NATHANIEL SOUTHGATE 8HALER.
813
^ -
• •
• •
f-
• _ •
• • •
••• « _•
• • • • ••
• f
( •
r •
^09918
• • • » ••
• • * • •
• • • • • «
• • •
• ••
*
• * *
•-•
• _•
• • •
• • • •
• • •
«
CONTENTS.
Page.
Prefatory note 219
Nature and origin of soils 221
Processes of soil formation 230
Cliff talus soils 232
Glaciated soils 236
Volcanic soils 239
Soils of newly elevated ocean bottoms 245
Physiology of soils 250
Effect of animals and plants on soils 268
Effect of certain geologic conditions of soils 287
Qlacial aggregation 288
Alluvial aggregation 288
Overplacement 296
Inheritance 300
Certain peculiar soil conditions .' 306
Swamp soils 311
Marine marshes 317
Tnle lands 320
Ancient soils 321
Prairie soils 323
Wind-blown soils 326
Action and reaction of man and the soil 329
Effects of soil on health '. 340
Man's duty to the earth 344
215
ILLUSTRATIONS.
Page.
Pl. II. View on the eastern shore of Cape Ann, Maasachusetts, showing
shore Hue stripped of soil materials by wave action 226
III. Glaciated rock surface from which the thin soil has been swept
away, eastern Massachusetts 228
IV . Effect of glacial action on a surface which has not yet been re-cov-
ered by soil 230
y. Precipices with talus of rock fragments passing downward into
rude alluvial terraces 232
VI. View showing varied rate of decay of talus formation in Tri-
assic sandstone schist near Fort Wingate, New Mexico 234
YII. Process of decay of soft rocks which are easily worn by flowing
water 236
YIII. Earthquake fissure in Arizona, showing the manner in which
these shocks may rupture the surface 238
IX. Process of decay in talus formation in much-jointed granitic rock.
Mount Lyell, Sierra Nevada, California 240
X. View showing the process of rock decay where the material con-
tains solid portions which are not readily corroded 242
XI. View of a mountain valley showing coalesced talus slopes through
which the river finds its way below the surface 244
XII. Talus deposits in a mountain gorge where the stream has slight
cutting power. Lake Canyon, California 346
XIII. Process of erosion of rather soft rock, the talus from which is
invading forest 248
XIV. Cliffs of soft rock without distinct talus 250
XV. Morainal front in eastern Massachusetts, showing the way in
which vegetation occupies a bowlder strewn surface 252
XVI. Drumlins or lenticular hills in eastern Massachusetts, showing
the arched outlines of these deposits 254
XVII. Aspect of a surface on which lie extinct volcanoes ; also showing
details of talus structure 256
XVIII. View showing rapid decay of lava 258
XIX. Process of decay of obsidian or glassy lavas near Mono Lake,
California 260
XX. Margin of a lava stream overflowing soil occupied by vegetation. 262
XXI. Summit of Mount Vesuvius, showing cone of coarse volcanic ash
lying upon lava which occupies the foreground 264
XXII. View near caves of Luray, Virginia, showing the character of
surface in a country underlaid by ca venis 266
XXIII. Broad alluvial valley in a mountainous district, the area partly
improved by irrigation ditches 290
XXIV. View of a mountain valley, showing the beginnings of the river
alluvial plains 292
217
218 ORIGIN AND NATURE OP SOILS.
Page.
Pl. XXV. Beginnings of allavial terraces in the upper part of the Camber-
I land River valley, Kentucky 294
! XXVI. Ox-bow swing of a river in an alluvial plain : the Ganges, India. 296
XXVII. View in the Dismal Swamp of Virginia, showing character of
vegetation in that district 312
XXVIII. Reclaimed fields in the central portion of the Dismal Swamp, Vir-
ginia 314
XXIX. Vegetation in the fresh-water swamps of central Florida 316
XXX. Form of surface in an elevated region south of the glaciated belt. 330
XXXI. View showing the gradual passage from rock to soil 332
Fio. 1. Diagram showing the history of a talus 233
2. Sections showing the two common varieties of glacial detritus 238
3. Successive states of a district where volcanoes are for a time active. . 241
4. Map showing comparative development of stream beds in a district
when it is forested and when the wood is removed 254
5. Diagram showing action of soil water in excavating caverns 257
6. Diagram showing one of the conditions by which soil water may
penetrate deeply and emerge as a hot spring 258
7. Effect of roots of trees on the formation of soil 270
8. First effect of overturned trees on soil 273
9. Final effect of overturned trees on soil 274
10. Diagram showing process by which a stone may be buried by the
action of earthworms and other animals 275
11. Effect of ant-hUls on soils 279
12. Section through the coarse alluvium formed beside a torrent bed 290
13. Section across a river valley showing terraces of alluvium 291
14. Section across alluvial plain on one side of a large river 292
15. Diagram showixig the effect of a layer of rock yielding fertilizing ele-
ments to the soil 296
16. Diagram showing the direction and rate of motion of soil 297
17. Diagram showing progress of fragments down a slope to a stream 298
18. Diagram showing relative state of soils in lower part of mountain
valley and in the ** cove *' at its head 299
19. Diagram showing successive variations in fertility in the soils of
central Kentucky during the downward movement of the rocks . . . 302
20. Diagram showing the lateral migration of streams in their descent
through inclined rocks 303
21. Section across ordinary lake in glacial drift 314
22. Diagrammatic section through lake basin showing formation of infu-
sorial earth 316
23. Section from seashore to interior of district recently elevated above
the sea level 317
24. Section showing the origin and structure of marine marshes 318
25. Section through coal bed 322
26. Section showing process of formation and closing of gullies on hill-
sides 332
27. Diagrams showing one of the ordinary conditions of water supply . . . 343
• •
» ^ m
• ••
THE ORIGIN AND NATURE OF SOILS.
By N. S. Shaleb.
PREFATORY NOTE.
The object of this report is to set before the general reader a some-
what popular account of the origin and nature of soils; to show the im-
portance of their relations not only to the well being of men but their
influence on the course of the physical and organic events which hav^ de-
termined the geologic history of the planet. It is also intended to show
that this slight superficial and inconstant covering of the earth should
receive a measure of care which is rarely devoted to it; that even more
than the deeper mineral resources it is a precious inheritance which
should be guarded by every possible means against the insidious degra-
dation to which the processes of tillage ordinarily lead.
The peculiar order of the relations of civilized men to the soil are
now the subject of serious discussion. More clearly than ever before
it is i)erceived that the roots of our society, like those of a tree, strike
deep into the fertile earth and draw thence the nurture which maintains
all its springs of life. The way in which the soil may best be made to
support the state, the laws by which it can most effectively secure this
need, the measure of governmental interference with the ownership of the
fields and forests, are now all matters of serious debate. In the cx)nsid-
eration of these problems it it desirable that the nature of the matter
under discussion should be well understood. We should as far as pos-
sible obtain a clear notion as to the way in which the varied soils stand
related to the needs of our people. It is of importance, for instance, to
know how much tillable land still remains in the unused reserves of the
inundated and arid districts of this country and how far these may pro-
vide for the necessities of the generations to come. It is equally desir-
able for us to know the extent to which the fertility of this superficial
coating of the earth needs the i)eculiar care which men give to their
personal property, but which they rarely if ever devote to goods which
are not endeared to them by absolute possession. The discussion of
these and many other con'elated questions demands a certain amount of
knowledge which in order to meet the need must be separated from the
219
V
« •
• • •
• • »
• • •
*••
•
• c
• •
220 ORIGIN AND XAXrRE OF JiOILS.
spei'ial learning or at least the speeial phases of the several sciences ot
geology, physics, chemistry, and botany, which are applied to the in-
quirieei relating to the c*onstitution and eiH>nomy of the soiL
It is a somewhat remarkable fact that while the scientific treatises on
soils are very numerous constituting, indeetl, a tolerably rich literatnTe,
the general essays on the subject are few in number and are, moreover,
almt^t without exi*eption, devoted either to the i*onditit>ns of some par-
ticular region or to a particular ch^ss of questions which demand in the
reader who is to obtain profit firom their pages a considerable amount
of training in chemical sineuce. So far as I have learned there is no
work in our own or in any other language which will give the reader
who has not had spei^ial tei*hnical training in the snbjet*t any connected
story concerning soil problems, which will in familiar phrase tell him
the leading and most important fiu*ts c^mceming the chemistry* physics*
and geoh»gie history of these depi^sits. The ikrmer who imfteratively
neetls to know something as to the part of the earth with which he is
dealing is, in the main, cinnpelled to rely upon personal or traditional
experience as the guide of his conduct. This body of inherited learn-
ing is doubtless of great value; it is indeed in the best sense scientific
as well as practical, tor it rests, as all true science does* on a series of
experiments; 3ret it is necessarily limited, for the reason that it is de^
riveil firom contact with the comlitions of a small field. For its best use
it needs the enlargement of view which comes from an understanding
of the general aspect of the subject and a knowledge of the experience
of other men in other regions who are dealing with the same class of
problems.
Where the people who till a particular soil have dwelt for centuries
upon the same ground, the mass «>f learning concerning it which is
gathered in tradition is usually very great, and in most cases pn>vides
better guidance fi>r the husbandman than any more rec«>ndite siuence
can afi^»rd him. The fi>lk who have summered and wintered with their
fields ^ many generatiomi know in most cases the efiVcts of diverse
means %^ tillage in a very complete way. The efi^e«'t of this um^stral
experience in such immemorially cultivated land u^ commonly shown in
the preservation of the ori;rtnal tertility of the earth or even in the en-
han«*ement \>i its returns by the skillful treatment which it Uiis received.
The pet>ple have in these cases learne«i how t4> husband and au^rmeat
the soil res«»urces, and a s4Hin4i public opinion ci>cnmaads a lar^e meas-
ure oi care in agriciilrure. In these countries the owner has himself
strufk Toi>t in the <knli he has come to love it as the s«Hirce of his
«»wn life and to U)«)k torward to the time when it will nurture his de-
si-endants* He may api)ear t4> the eye as a stui>id peasant, but he i^*
ill most cases learned in all that relates t4) his acres from his own ex-
I>erieuce and the Nxly of intbrmatiou which has come down t*) him from
the pik<t.
It bi »>therwise in thL* new world of America. Save here and there
BHALEB.] CONDITIONS OF INQUIRY. 221
in the parts of the country longest settled, the traditions concerning
the soil of any district are comparatively meager. It is indeed rare to
find a farm which has been tilled for as much as a century by the mem-
bers of one family. The larger part of the land, particularly that of
the Northern States, has been occupied but a few years by the people
who now possess it. A great i)ortion of our agriculturists have -but
recently come upon the fields which they cultivate. Thus among the
farmers of the continent there is no extended experience in the condi-
tions of the soil they till. Left to such lessons, it will require genera-
tions to gain that information which the history of other fields might
readily and immediately supply. It is in this way that science can best
help in practical affairs such as agriculture and mining, viz, by pre-
senting the results which have been gathered over a wide area of
ground for the guidance of laborers in a particular field.
• One of the greatest improvements in modern agriculture consists in
the use of various mineral manures which within the lifetime of many
active men have been made elements of commerce. Although the j^rofit
of these resources is in most cases to be quickly and cheaply determined
by actual trial, it is, nevertheless, important that those who are inter-
ested in farming should know something concerning the nature and
origin of these geologic fertilizers in order that they may be prepared to
discover them in their own districts. There can be no question that at
a great number of as yet undiscovered localities in this country there
are deposits which will serve well as sources of materials for the refresh-
ment of the soils. As far as seems practicable within the limited scope
of this essay, care is taken to point out the conditions in which such ma-
terials may be expected to occur.
Although it is hoped that the practical needs of many persons may
be served by this essay, the main intent of it is to afford a clear, sim-
ple and connected idea of the place of the soil in the economy of nature.
So far as this can be done it will tend to ennoble the conception of all
those relations with the earth on which the daily life of mankind de-
pends, and on which the whole future of our civilization must rest.
To obtain this end it will be necessary to devote the larger part of the
essay to a study of the origin and nature of soils, showing how they
originate, and the steps by whicli they are continually reformed. Only
by a careful discussion of these points can the true nature and im-
XK>rtance of this covering be made plain.
NATURE AND ORIGIN OF SOILS.
Many of the most noteworthy features of this world are, by their ever
present nature, in a way concealed from us. The starry depths of the
heavens afford a spectacle which would overwhelm the minds of men if
they were revealed to us but once in a generation, but from the famil-
iarity of the vision they nightly pass unregarded. In a like manner
the soil beneath our feet, becjiuse we have been accustomed to its i)he-
222 ORIGIN AND NATURE OF SOILS.
iiomeua for all our lives, appears to us commouplace and uninteresting;
it seems a mere matter of course that it should everywhere exist and
that from it should spring the manifold forms of life; that into it the
dust of all things should return to await the revival of the impulse which
lifted them into the living realm. Now and then a x>oetic spirit, antici-
pating with the imagination the revelations of science, has spoken of
the earth as the mother of all; but the greater part of mankind, those
who are well instructed as well as the ignorant, look upon the soil as
something essentially unclean, or at least as a mere disorder of frag,
mentary things from which seeds manage in some occult way to draw
the sustenance necessary for their growth. Any chance contact with
this material fills them with disgust, and they regard their repugnance
as a sign of culture.
It is one of the moral functions of science to change this attitude of
men to the soil which has borne them; to bring men to a clear recogni-^
tion of the marvel and beauty of the mechanism on which the existence
of all the living beings of the earth intimately depends. This end it
attains through the clear views which it opens into the structure and
history of the earth by removing the dull conception of mere chance
which we almost instinctively apply to the phenomena of nature, and in
its place giving an understanding of those processes which lead to the
order and harmony of the universe. In no part of this great work of
ordering and ennobling nature in our understanding is modern learning
doing a better or more profitable work than in removing the veil of the
commonplace with which long and ignorant familiarity has wrapped this
earth, hiding its dignified meaning trom the understandings of men.
Though this task is but begun, enough has been accomplished to insure
in those who have an appetite for such truths a nobler conception of
this sphere, a new and imposing sense of the relations which they them-
selves and all their living fellows bear to the earth which has nurtured
them.
This view of the moral relations of men to the earth is attained by the
method of science in a simple way; following step by step the history of
the earth's features and noting the processes by which they have taken
form, there gradually develops in the mind a sense of the activities and
the relations between the forces which have shaped its growth. No
sooner is this inquiry begun than the mind ceases to look upon this
sphere as a dull matter-of-course. Every event in the history is seen
to have been determined by well adjusted modes of action. Each of
these events blends its influence with every other so that the whole
sphere moves forward in the process of its evolution, a vast array of
forces perfectly ordered in their ongoing, steadfastly winning successes
in organization and bringing all of its activities to a higher plane of
existence.
It is beyond the compass of the human mind at once to conceive the
course of the many different fields of this earth's progressive activities.
8HAiJtB.I SUBSTANCES COMPOSING SOILS. 223
We have to limit our inquiries to some particular part of the vast realm
in order that the number of the considerations may faU within the com-
pass of our understanding. The student of the earth may select any
one of the dominions of its mechanism and from the study win an ex-
alted conception of the wisdom and beauty of its processes. On many
accounts the soil covering is the best field for the beginner of such
inquiries. The facts with which he has to deal are in general of a
simpler and more evident nature than those which are afforded by the
concealed portions of the globe. They are everywhere presented and
are to a great extent open to the light of day, while the student of the
earth's successive periods or of its mineral deposits is compelled to seek
beneath the surface and in many different lands for the phenomena
he deals with. The observer of the soils everywhere finds the part of
nature with which he is concerned close about him and accessible to his
inquiry, as are no other parts of the geologic field. AU that is needed
is an interest in the problem and an easily acquired training in certain
simple methods of observation to fit any one for the study of the more
evident phenomena of soils.
As the greater part of the soils of the earth in their natural condition
are forest clad, we shall begin our inquiry with the portions of the earth
which are covered with woods. The reader should, however, bear in
mind the fact that a large portion of the lands are destitute of timber,
and are either covered by a luxuriant growth of lowly plants, as in the
case of the prairies, or in arid districts may present a very scanty growth
of vegetation. In certain very rare cases the surface bears a true soil
which does not support any vegetation whatever; but in such instances
we may be sure that a recent climatal change has led to the destruction
of a vegetable coating which originally existed in the district.
In beginning a study of the soil covering it is well to gain an idea as
to the nature of this substance of which it is ordinarily composed. In
this first step it will be useful to select a handful of ordinary soil from
any convenient place, taking care that it is from within an inch or two
of the surface and from a place where it has not been disturbed for a
century. It is best it should be virgin soil; that is, unaffected by the
processes of tillage. The naked eye commonly shows us that the mass
is composed of two distinct kinds of materials. In part it is made up
of decayed vegetable matter, portions of which so far retain their living
shape that we can easily see that they are derived from leaves or twigs.
Prom these discernible bits, by progressive decay, the vegetable matter
shades down to less and less distinguishable form until it appears as an
unorganized blackish mold. Mingled with this dark waste of rotted
vegetation there are more or less distinct fragments of a stony nature
in the form of sand or pebbly matter. If the sample has been taken
from an old forest bed these bits of rock may be so rare as to escape
observation; taken from a lower part of the soil they will always be evi-
dent, if not to the eye, at least under a simple microscope, or, if that is
224 OKIGIN AND NATURE OF SOILS.
not couveiiient, they may be felt between the tet^th as gritty particles.
Observing them closely we find that, however .small, they are more or
less angular fragments of rock, generally a good deal decayed on the
surface, often so much changed that they fall into dust at a touch.
The magnifying glass shows that the process of decay is fracturing all
these fragments along their structural planes, joints, or cleavages, and
this indicates that some action is at work which serves to break up the
st/ony matter of the soil into an ever finer state of division. That this
action is in a way peculiar to the soil is shown by the fact that if we
take a sample of finely divided rock, as for instance from any soft sand-
stone or other like dex)osit lying at a considerable depth below the soil,
we find that its grains do not exhibit this progi^essive decay. We shall
hereafter note how this breaking up of the stony matter is brought
about.
In order to see in a clear manner that the soil is not a mere mixture
of decayed organic matter and of broken-up rock it will be well for the
observer to make two small experiments which will throw much light
uiK)n this i)roblem. In one experiment, a sufficient quantity of the rock
lying be'ow the original soil at such depth as to preserve it from the
chemical infiuence of the superficial materials should be taken and re-
duced to a state of division like that of the stony matter of the soil. In
this seeds of some grain-bearing plant, such as wheat, should be sprouted
and kept duly moistened with distilled or rain water. It will be ob-
served that while the seeds readily germinate and enter on the process
of growth the plants soon become stunted and fail to produce their fruit.
If we then take decayed woody matter, such as forms the other com-
ponent 6f the soil, carefrdly excluding all mineral materials from the
mass and, as before, sow it with grain, we find that there also the plants
grow for a time sustained by the nutriment contained in the seed and
the trifle of sustenance they find in the materials about their roots, but
they likewise fail to come to ftill maturity. It is not indeed necessary,
to i)erform these exj^eriments artificially. We may often observe them
in the fields. On the storm-blown places where the natural soil has
been removed by the wind and bare sand exposed we may observe that
the seeds of the tough wild grasses, which lodge upon this material,
sprout as in the suggested experiment with powdered rock, but die be-
fore they blossom. In other places we may see where some deep mossy
bog has been recently drained and an effort made to reduce it to culti-
vation. Hardly any flowering plants will ripen their seeds upon it, the
pure vegetable mold evidently being unfit for this nurture. It is nec-
essary to remove this swamp deposit by burning or by allowing it to
decay until it is so thin that the plow can mingle the humus with the
rocky matter which lies beneath the layer before any green crops can
flourish upon it.
Although it is in general true that decayed organic matter is neces-
sary to fit a soil for the uses of vegetation, it should be remarked that
8HALKB.1 AREAL DISTRIBUTION OF SOILS. 225
in certain instances the earth may yield its mineral stores to vegetation
even where there is no trace of decayed organisms in the mass. This
condition occurs most commonly in arid lands which by irrigation have
been made fit for tillage. Such soils, even where destitute of organic
matter in a state of decay, often have a relatively largo proportion of
their mineral ingredients in a state in which they may be assimilated
by the roots. The reason for this exceptional condition is perhaps as
follows, viz : Even in the desert districts there is a small amount of
rainfall, enough to provide the soil at certain times of the year with a
share of water. This water effects the decomposition of the mineral
matter in a slow way, but as the substances made ready for solution are
not removed by plants, nor to any extent carried away by underground
movements of water, they remain stored in the earth and are ready for
the use of vegetation when the field is provided with water.
In some parts of the Southern States, notably in Florida, soils which
contain scarcely a trace of organic waste at the depth of say an inch
below the surface will nourish vegetation. In this case the solution of
the mineral substances is probably in good part effected through the
action of the water which, in its course through the thin layer of de-
cayed vegetation, takes up the acids which facilitate, though they are
not absolutely necessary to, the decay of the rocky matter.
These artificial or natural instances appear to show us that true fer-
tilized soils are not usually made of either stony matter or vegetable
materials alone; that what is needed is a mixture of the two substances.
Similar experiments, or, in their place, observation in the field, will in-
dicate that some time must elapse after the mineral and vegetable
materials are mingled together before the soil becomes adapted to the
growth of plants which produce fruits important to man; it in general
requires a year or more for the results of the mixture to be evident.
The general meaning of this evidence is plain ; it is clearly to the efiTect
that true fertilized soils, at least those from the point of view of human
interests and needs, are the result of some reaction between the decayed
organic matter and the broken-up bits of the solid earth with which
it is commingled in varying proportions according to the circumstances
of its development. Before we proceed to consider the natural history
of soils, in which task we shall endeavor to show the way in which this
commingling of their organic and inorganic components has been
brought about and the chemical influences arising therefrom, it will be
best for us to examine in a brief way into the effects of this mixture of
these decayed materials derived from the remains of forms which were
once living and from the lifeless rocks. In tliis way we shall see some-
thing, at least, of the importance of the questions with which we are to
deal, and shall at the same time have a chance to note the problems
which m our further inquiries we should seek to solve.
One of the most noteworthy features of soils is their wide extension
over the surface of the lands. It is only in a very small portion of the
12 GEOL 15
226 ORIGIN AND NATURE OF SOILS.
land area that they are absent. The nature and origin of these frag-
mentary and on the whole insignificant soilless are^is should be noted^
for the facts are very instructive. We observe in the first place that
soils are wanting on those surfaces of the bed rocks which are swept by
moving water in such manner that the detrital materials can not remain
in their natural position. The shores of the existing sea and of some
ancient sea margins within the section beaten by the waves, the rocky
beds of rivers and torrents, the steep parts of mountains where the rain
urged downward by gravity clears everything before it until it flows on
the bed-rock, are instances of this action (see PI. ii). Also, where rocks
are steeply incUned, the eflfect of frequent earthquake shocks is to urge
all loose materials in ^ sliding motion to the base of the declivity.
Again, in regions from which glacial ice has recently disappeared it
happens that occasional patches of bed-rock are left without any of the
detrital coating which is usually deposit^'d on such surfacei^ (see PI. iii).
In regions overflowed by lavas derived from recent volcanic eruptions
we now and then find that the once fluid but now solid rock has not yet
become soil covered (see PI. xxi). Lastly, in certain places where the
soil at times when the wind blows violently is very dry and maintains
at best but a scanty vegetation, the moving air may swe^ep it away.
Notwithstanding this considerable list of conditions which may lead to
a soilless earth, at least nineteen-twentieths of the land areas are occu-
pied by a coating of commingled rocky and organic matter of sufficient
thickness and fertility to afford sustenance to a varied vegetation and
in a greater or less measure, if careftdly tUled, to contribute to the ne-
cessities of mankind.
However these soils may dififer in their character we shall find that
they all have the common feature above noted of containing an admix-
ture of materials derived from the decay of the firm-set underlying
earth and similarly decayed fragments of plants and animals; the ani-
mal remains are less evident and important, but they are present in all
soils and in many of them are a considerable element in their composi-
tion. On the adjustment in the proportions of these diversely originating
materials depends to a great extent the fitness of the earth in the par-
ticular region to bear an abundant vegetation, whether planted by
nature or by art. The variations in this regard largely depend on the
operation of the natural agents which serve to bring about and main-
tain this association of the two elements, the organic and the inorganic,
which compose the soil.
The extension of the soil coating of the earth is not more widespread
or more evident than its importance to the organic life of the land.
Nearly the whole of the x)lants other than those of the sea and the lichens
and mosses require as the first condition of their existence that there
shall be a soil beneath them from which they may derive the mineral or
ashy parts of their bodies and the water of their sap. On the arid soil-
less lands of the desert or on lava rocks we may find a variety of the
8UALKB.] DEPENDENCE OF ORGANIC LIFE ON SOILS. 227
rootless non-flowering plants such as the " tripe de roche,'' a species
of lichen, or the *' poverty grass," another similar plant of the sandier
fields of New England, but unless there be a distinct though it may be
thin soil, none of the higher plants, especially those of importance to
man, will grow there. So, too, on the bogs where the vegetable mold
is deep and the plants can not strike their roots through it to the under
earth and where the deposit is so placed that mineral matter can not be
washed in from the land or blown on by the winds, we find the vegeta-
tion to consist of species which, like the water-loving mosses, have but a
small amount of mineral matter in their comxK)sition. This mineral
matter they give, when they decay, to the swamp water, whence it is
returned to the growing forms. No plants having nutritious seeds or
fruits, none yielding strong fibers or endowed with other qualities mak-
ing them immediately valuable to man or useful to him because they
serve the needs of food for his domesticated animals, will flourish in
these swamps, where the depth and purity of the vegetable mold ex-
cludes the roots fi'om the advantages of a true soil. It is by such
observations made plain that were it not for the peculiar conditions
which are afforded by this admixture of the debris of the uuderearth
and of organic bodies, the higher plants which afford sustenance to
man and to all the higher animals as well would have no place on this
sphere.
A little consideration of the relations of the higher animals to plants
makes it clear that all the advance of the earth's life above its simpler
forms depends upon the existence of moderately fertile soils such as
produce food fit for the nurture of the higher forms. They could not
have developed if the world had afforded no better provision for them
than the lichens of the rocks or the mosses of the peat swamps. We
thus see that the soil is really the immediate source not only of the
sux>erior kind of plants which feed in the soil, but also of the animals
which depend upon them. If the plants, such as those which produce
fruits, grains, or nutritious herbage, had not had this field for their
development there would have been no chance for the evolution of the
series of animals which have led life up to the estate of man to find a
place upon the earth. Important as the effects of the soil are to more
advanced beings, they have been almost as important to many of the
lower orders of life. Of the vast array of insects existing on the earth,
the species of which are to be numbered by the hundred thousand, the
greater part likewise dei)end for their nutrition either on the food
they obtain from the soil nurtured on higher plants or on other animals
which themselves feed on such vegetation; only a few lowly forms can
subsist on plants which do not require true roots for their support. The
bees and ants, nearly all the butterflies and moths, in fact all but a
trifling remnant of the insect world, need the conditions which the soils
bring about quite as ifhich as does man or his kindred among the mam-
mals.
228 ORIGIN AND NATURE OF SOILS.
It is not alone on the relations of the soil to the life of the land, how-
ever, that we must look for its action in the economy of the world ; those
relations, though most important and apparent, are not the most far-
reaching of the consequences which arise fi'om the mingliug of decayed
organisms with the stony matter of the earth. To perceive these we
must look in succession at the conditions of the seas and of the rocks
which lie in the depths of the earth. We shall find that on these appar-
ently remote realms the influence of the soils is felt in many and inter-
esting ways.
On the floors of the seas there is no soil coating; there is on these
surfaces a quantity of detritus worn from the land, cast into the seas
by volcanoes or laid upon their bottoms by the decay of organic bodies,
the whole forming a layer which in many ways resembles the soil cover-
ing of the lands, but it serves no purpose in nourishing vegetation.
The true algae or seaweeds have no roots; they absorb through the sur-
face of their bodies the materials which ordinary plants procure by
these processes. As the waters of the sea, and in a less considerable
way the fresh waters in our lakes and streams, (K)ntain a considerable
amount of mineral matter wliich they readily yield to these aquatic
plants, this lowly vegetation has not been comi)elled to invent the
sx>ecial underground structures which take the ashy material neces-
sary for their growth from the soil waters. When plaiits originating in
water forms were by the course of their develoimient transferred to the
land, they found in the rain which fell upon their leaves no mineral
materials to serve their needs, and therefore the parts of their surfaces
above ground abandoned the function of absorbing mineral matter and
only the under earth parts retained those absorbing functions wliich
were common to the whole of the seaweed, and these roots jierformed
the office for the whole plant. As we shall see hereafter, it is in a con-
siderable degree to the penetration of the roots that we owe the char-
acteristic features of the soil ; therefore, while the materials accumulated
on the sea floor resemble in their fragmentary and unorganized form
those of the land surface, they really differ from them in a distinct and
imxK>rtant way.
There are other differences in the constitution of the sea-floor deposits
which separate them from the true soils; thus on the ocean bottom there
is no current of water through the detritus; none of that alternate
wetting and drying which is of very great importance in the economy of
soils. Only a few of the root-bearing plants have accustomed themselves
to draw nourishment from the debris dei)osited on the sea floor, and
these, like the mangrove tree, can do so only in the marine mud next
the shore, which is in large measure composed of waste washed in from
the neighboring land. Furthermore, though there is generally a soft
layer of a muddy or sandy nature lying on the floor of the water areas,
this matter is always passing from the incoherent to the compact state,
while on the surface of the lands the process is exactly reversed^ the
change being from the solid condition of the rocks to the loose state of
SHALBB.1 CONTRAST BETWEEN CONDITIONS OF LAND AND SEA. 229
the soil materials. In a word, the marine conditions are those in which
the rocks are being integrated or built up, while on the land the state
is that of disintegration. It happens that these two contrasted proc-
esses alike for a time afford materials of a somewhat similar apx>ear-
auce, though in fact the state of the respective deposits are essentially
dissimilar.
In the i)rocesse8 which go on beneath the surface of the soil of the
land and below the i)seudo-8oil or growing bed of the sea floor, we And
widely contrasted phenomena. Thus below the soil and thence indefi-
nitely downward we find that the rain-water finds its way through
the innumerable crevices of the earth, carrying agents of change along
with it. In this manner it produces the ordinary caverns of our lime-
stone rocks and has a large share in the formation of mineral veins
and other alterations in the original character of the rocks. In many
cases these soil effects are propagated downward for hundreds if not
thousands of feet; in many parts of the world, in all portions of the
land, indeed, where the surface has not recently arisen from the sea or
been in late ages scraped away by the glaciers, this downward-going
influence of the soil is clearly marked to a great depth, producing in
general a profound decay of the rocks, which often become so much
softened that beds originally hard granite or tough mica schist may
easily be cut into with a miner's pick. No sucli effects arise from the
presence of the detritus of the sea floor, for the reason that here is no
opportunity for the waters to penetrate downward from that level in
the manner which occurs beneath the land.
This contrast between the conditions of the sea floor and those of the
land in all that pertains to the effects of the detrital layer, if we consider
it well, points to the obvious and important general conclusion which
will be enforced by all that we shall have hereafter to consider, viz,
that the life of the land in a singular way depends upon the destructive
processes acting on the portions of the air-bathed parts of the earth's
crust. It is to the ceaseless wearing down of the land that we owe the
formation and preservation of the wonderful mixture of decayed rock
and organic matter which forms our soil. This is one of the most
beautiful and significant facts of nature; it shows us that the processes,
which from a short-sighted view we term destnictive and associate with
death, are in fact but steps in the system of advance which lead matter
from the lower mineral state to the higher condition of organic forms.
The foregoing inadequate sketch as to the general place of soils in
nature will serve to show, at least in outline, the importance of the
problem which they present, and also to indicate the path which our
inquiry should pursue. We shall now undertake to trace the genesis
of soils in the different conditions in which they come into existence,
beginning with instances in which the observer may verify the state-
ments in almost any part of the world, and then passing to those cases
in which the process is not so easily seen but has in a measure to be
inferred from geological study.
230 ORIGIN AND NATURE OF SOILS.
PROCESSES OP SOIL PORMATION.
From what we have already considered it is evident that soils are not
original features of the hind areas, but have been in some way produced
after they were elevated above the sea.
Nearly all the areas of the continents and islands are known by geolo-
gists to have been formed beneath the sea and then uplifted above the
level of the water. The process of their soil-making necessarily began
when the rocks of which they are composed were clad with land vegeta-
tion and subjected to the manifold influences of the atmosphere. From
time to time, the soils, after they "^ere formed, were swept away by vari-
ous chances, as when glaciers removing the soft materials left the rock
bare, where earthquake-shocks have caused the soil to slip from steep
places into the valleys, when lava floods or volcanic ashes have buried
X>ortions of the surface beneath layers of rock, or in a far less important
but for us significant way, when man for some purpose has stripped away
the soil from the surface of a part of the earth. To the observer these
instances of the artificial baring and subsequent covering of the bed-
rock again with soil are particularly interesting for the reason that they
can be more easily understood than the larger work done over culti-
vated areas; the effects are also more computible in these partly aHi-
flcial cases than those of the purely natural sort. We shall therefore
begin our studies with this small class of soils which we may observe
to be forming in old quarries or other places where the detrital coating
has been for many years stripped away and the surface left to the i)ro-
cesses of nature. (See Pis. iii, iv, xviii, xx, xxi.)
In all the older parts of this and other countries, where the rocks be-
low the soil are of a nature to make it worth while to quarry them,
abandoned pits can be found, and the length of time which has elapsed
since the area of the bare rock was left untouched may usually be de-
termined with tolerable accuracy.
Visiting any such old excavations where the rocks have not been
stripped away for, say, ten years, we observe that on the surface of the
stone there is a discoloration which gives it a hue differing clearly from
that exhibited in the neighboring quarries where the faeces have been
recently disclosed in quarrying. Examining the rock closely with a
glass the mineralogist can detect the beginnings of the decay arising
from the exx)osure of the materials to the sun's heat and to frost and
rain. The feldspar shows signs of the change which reduces it to the
state of kaolin, a very soft material, and the hornblende exhibits marks
of rusting due to the combination of the iron which it contains with the
oxygen of the air. These changes are least on the vertical faces and
steep slopes of the quarry; on the level surfaces they are much more
advanced ; we can indeed find spots where the water stands in shallow
pools, where the decay has advanced to a point that a little sand and
mud gathers as a film on the stone, the coarse grained fragments being
sHALKBl PROCESSES OF SOIL-MAKING. 231
the half-shaped crystals of quartz and the finer matter the decayed
feldspar.
All over the surface of a quarry which has been abandoned for as
much as ten years we find that tiny lichens have attached themselves
to the stone and from it drawn th6 small amount of mineral matter
which they require for their bodies; this they can not do except for the
decay whi(ih has served to render the material soluble. Even where
the unaided eye fails to observe this vegetable growth an ordinary
magnifying glass will generally reveal it. At the foot of the slope of
rock we may notice a small talus of debris which has washed from the
rocks above; examining the mass we find it to be comx)osed in part
of stony material, the crystals of which have become detached by decay^
and partly of the remains of the lichens which are constantly dying and
contributing their waste to the deposit. That the accumulation thus
formed is a true bit of soil is clearly shown by the fact that when it is
kept moist it affords a foothold for many small flowering plants. The
crevices of the rock formed by the joint planes and other fissures are
often filled with the debris which has been washed into them by the
rains and blown there by the winds and thus affords points of vantage
for many flowering plants, which in the moist springtime are sufficiently
nourished to flower and ripen their seeds, though in the dry and heated
season of summer they wither away.
The share taken by the winds in bringing about the accumulation of
dust in ancient quarries is often considerable, but in a verdure clad
region like New England the detrital material is usually derived from
the artificial cliffs of the quarry.
In the older quarries, the stone of wliich has been exposed to the ele-
ments for 50 years or more, we find the same process of decay much
more advanced; the heap ofddbris begins to creep up the slope and
sustain larger and more luxuriant plants; the rifts in the rock are here
and there occupied by species of trees which tolerate occasional droughts
and their roots are wedging the fractured stones apart so that some
fragments have fallen to the base of the slopes. In this work the frost
plays also an important part, thrusting the masses asunder as it ex-
pands in freezing as eftectuaUy as the process is accomplished by the
quarryman's wedges and hammers, though more slowly. We note also
the fact that the lichens are larger, and evidently better nourished,
than in the case of the first quarry examined, and they are therefore
yielding more vegetable matter to the increasing talus. In the moist
places the mosses are spreading upward from the base of the cliffs; with
their spongy mass they hold water even in tolerably dry times, so that
the rock is gradually being enveloped in a mantle of their growth. On
the surface of this mass the debris worked from the rocks is constantly
gathering, so that the coating affords sufficient soil material for the
supi)ort of many plants, such as our huckleberries and other forms of
flowering vegetation. These by their annual contribution of leaves
232 ORIGIN AND NATURE OF SOILS.
and stems add Btill more to the increasing coating of commingled rock
waste and decayed organisms.
From the asjject of old quarries to that of natural rock surfaces lefb
bare of soil at the end of the last glacial period is an easy transition for
the observer to make. On the fields of glacially bared rock, from which
the ice has scraped and rubbed away the debris which once covered
them, we may find every stage of the healing process which takes place
when the solid parts of the earth have been stripped of their soil cover-
ing. The variety of conditions depends <m the resistance which the
rocks present to the agents which tend to break them up and in an im-
portant way on the nutritive value which the broken-up stone has for
plants. Thus it is when the rocks are composed of quartz or other
forms of pure siliceous material which is little afFe(».ted by the atmos-
phere, especially where, as in compa(*t quartzites and sandstones, tlie
stone seems at times to bid defiance to the elements. As in the case of
the rocks of this nature near Sugar Hill, New Hampshire, known as the
" Thrashing floor," and the innumerable other instances in the region of
crystalline formations in northern North America, the surface is so
little decayed that it still bears the finer marks of the glacial scratch-
ings, though, in the thousands of years which have elapsed since the
glacial period, it has had no other protection against the weather than
a thin sheet of moss and lichens which was in the course of time formed
on the surface, (See Pis. iii, iv, and xxxi.) A little decay was required
in order to support this thin growth, but the rotting has not been at
all sufficient to remove a tw^entieth of an inch in depth firom the stone.
There are in the aggregate in the northern part of this continent many
thousand square miles of rock of this exceedingly resisting nature,
which, though affording very little mineral matter for the formation of
soil, still has furnished enough to maintain a scanty vegetation. The
fact is that where there is but a small amount of material yielded by the
soil to supply the ashy matter for plants the precious store is effectively
retained by the vegetation, each plant deriving its supply of ashy mat-
ter mainly from the decayed bodies of its predecessors.
CLIFF TALUS SOILS.
From this condition in which the least possible soil making has been
effecti^l in the vast time which has elapsed since the glacial period, we
may in a region underlaid by rocks of varied hardness, such as the
glaciated region of New England affords, find every gradation in the
measure in which the rocks have been brought into the condition of
soil. Generally the decay of rocks has been great enough to furnish
soil sufficient to maintain a tolerably luxuriant vegetation. But it
happens in some instances that, while the rock breaks up rapidly, the
size of the fragments is on the average too large to permit them to be
used in soil making. Tliis condition occurs where the rock is rifted by
many joints or otiier divisional planes so that it breaks into a multitude
11
ri
n
bhil™.] history of cliff talus soil. 233
of fragments of considerable bnlk. These bits of stone accnmulate at
tlie bottom of the cUHh, forming n Btee|> rocky tains into tlie interstices
of which the finer matter yielded by decay penetrates below the level of
daylight, so that the plants can not convert it into soil. We may
observe that each of these masses of stone la attacked by lichens which
are doing their fit work; but before tliey have time to accomplish the
task the surKice is covered with new falls from the overlmnging cliffe.
Usually we And tiiat near the lower margin of this talua the plantJi have
managed to stretch the mantle of vegetation over its surface, and
though from time to time rock avalanclies invade a portion of the field
tlms won to the use« of life, the growth gradually creeps up the slope.
With each downfall of material ft^m the precipice the talus rises uearor
to the top of the cliif, until in the end the face of the escan>nient is
buried in its own riibbisb. (See Pis. V, VI, Tli, IX, XI, xit, and xm.)
m. ■_ __> --t j..^-... Tjjjiiiages to
interesting
SiS follows,
the stones
cashed and
lan titles of
3 or other
The whole
act that it
.rface that
•atien
ock,blt.Ulta,e,ilemmyi!d iwrtion of cliff;
the roots can not seize upon it, is excellently fitte<l for the sustenance
of plants. Seeds which germinate in the depths of the rubble die before
their shoots can escape above the darkness. Gradually, however, aa
the talus climbs up the side of the cliff and the annual f contributions of
fragments grow less considerable, the lichens seize on the surfaces of
the stone and add their contribution to that obtainetl from other sources,
and all the while fragments of rock are decaying and adding to the
accumulation. Finally the fine debris rises to the level of the daylight,
the see<ls of the plants of most vigorous growth take root and flourish
in what is really the very rich soil. Not long after the vegetation
234 ORIGIN AND NATURE OF SOILS.
secures a good foothold, the mass of raiu becomes the seat of a heavy
growth of large trees. Such talus slopes, indeed, are often covered by
very luxuriant forests.
The soils formed on talus slox>es are generally well suited to natural
vegetation, though for a time they are not at all adapted to the uses of
the plow. The large fragments of rock inclosed in the somewhat
dispersed earth gradually decay ; whenever a crevice forms, the roots of
the stronger growing plants send their flbriles intotheopening and these,
expanding with great energy as they grow, rupture the mass and so
extend the surfatie exposed to dox^ay. To conceive of the importance
of this action we should bear in mind the facrt that in such a soil there
are usually within the limits of an acre millions of these root processes
searching for every cranny in which they may find nourishment for the
plants to which they belong; no chance escjajM^s tliem; no sooner is the
slenderest crevice opened than they inviide it, and if they find suste-
nance there they burst the ma«s as with a wedge. So effective is this
process of external decay combined with the riving action of the root
that unless the fragments of whi(»h they are comiwsed are very unyield-
ing these talus deposits are rapidly cx)nverted into de«p and fertile
soils. They are rarely well suited for ordinary tillage for the reason
that as long as they are stony they turn the plow or spade, but they
are excellent nurseries of timber and admirably suited for the culture
of the grape; some of tlie best vineyards of the world are situated on
slopes of this descrii)tion.
It often happens that dei)osits formed of detrital materials are shaken
down the sloi)es on which they rest by violent earthquakes. It is char-
acteristic of regions which are much affected by such shocks that the
detritus at the foot of cliffs is reduced much nearer to a horizontal atti-
tude than it ordinarily assumes. It is naturally impossible to give any
grax)hic representation of this action in the case of debris lying on steep
slopes, but an adequate idea as to the eflSciency of these disturbances in
moving debris may judged from the fissured character of the field shown
in PI. VIII where the earth has recently been broken by an earthquake.
The above description as to the method in which cliffs gradually be-
come covered by talus slopes is mainly applicable to the Cvscarpments
which are developed in countines which have been subjected to the
action of gla<cial ice, and to those which have been formed along the
banks of rivers which after a time have worked away from the bases
of the steeps which they carved. There is another class of cliffs, such
as are abundantly found in regions south of the glaciated fields, where
the i)recipices are due to the fact that the materials of which their
faces are formed are rapidly piissing into solution and are borne away
to the streams. In such cases the cliff usually exhibits hardly a trace
of true talus, for the reason that the fragments in their divided state
decay even more rapidly than the firm-set rock whence they are de-
rived. Such cliffs retreat across the country, leaving at most a thin
J.
8HALEB.] FORMATION OF SOIL ON GLACIAL DEPOSITS. 235
layer of very bard materials as a sheet upon its surface. Very often
nothing whatever is left to denote the ancient positions of the escarp-
ment talus (see PI. xiv).
The study of the formation of soils on rock taluses leads us naturally
to another condition in which soils are developed in confused masses of
rocky matter, i. e., where they form on the waste left at the close of the
glacial period in the regions over which the ice has moved, or in which,
though the field may have been in front of the glacier, the debris it pro-
duced has been spread. Clearly to understand the work done under the
peculiar conditions of the glacial epoch, it will be well for the observer
to know something of the living ice streams, as they are exhibited in
Greenland, Norway, or Alaska. From the abundant studies of their
action in these and other countries, it has been made plain that the fi:rat
effect arising from the presence of these singular masses of solid water
on the surface of any district is to strip away the soil and other inco-
herent deposits of its surface, the waste being sent forth beyond the
limits of the field by the streams of fluid water which flow from beneath
the icy sheet, or they are pushed forward as by a scraper, or conveyed
in the mass of the glacier to its front and there dropped on the ground
as the mass melts away. When one of these glaciers of to-day has
maintained its front a considerable time in one x)osition, we find there
a heap of stones and coarse sand which has been shoved forward by
the movement of the slow-going streams or carried in its mass and
dropped at the ice front. The greater part of these stones are smoothed
by the ice carriage, and all the matter in the moraine is entirely with-
out vegetable growth and usually deprived of finely divided rock, such
as sand of small-sized grain or mud, this much divided material having
been washed away by the streams of water which flow from beneath the
glacier or over its surface, these streams carrying away all but the
coarser fragments of the rock (see Pis. rv, xu).
In Switzerland, and most other coxmtries where glaciers exist, they
are now slowly retreating up the valleys they occupy, with occasional
interruptions in which they readvance for a short distance, so that
these frontal moraines are being constantly left to the action of the soil-
making 'agents. No sooner is the mass of stones deserted by the ice
than the great army of plants invade it. First comes the skirmish line
of the lichens, which, springing from light spores easily wafted through
the air, seize upon the rough places along the stone. When, as is so
frequently the case, these fragments have too little fine material be-
tween them to fill the interspaces, the process of soil-making is slow; it
goes on as in the formation of the rocky talus before described, by the
falling in of decayed bits of lichen, the blowing in of leaves, and the
slow decay of the bowlders which form the mass. As the bowlders are
composed of hard rocks, that by endurance have been able to withstand
the violent disrupting action to which they were exposed in their jour-
ney in the ice, they break up much more slowly than the fragments
236 ORIGIN AND NATURE OF SOILS.
formed in an ordinary talus. So gradaal, indeed, is the process of de-
cay that in the case of many of these moraines left in New England
and other parts of the United States by the ice of the last glacial
period, the bowlder heaps have not yet had their interspaces filled by
material to the level where the plants can make use of the debris and
convert it into soil. It is sometimes possible to creep down into the
cavern-like recesses of these moraines and see the accumulation which
is gradually filling the crevices and slowly rising to the surface of the
mass. We may in such places observe that the fragments are yielding
a more or less considerable amount of debris to the soil which is accu-
mulating in the crevices. A large part of the morainal matter left by
the glaciers of the ice age has in this way been brought into a state in
which trees can find root between the fragments; other portions, where
the erratics are large and enduring, still retain the aspect noted in PI.
XV, but in all of these the process of crevice filling is going on, and in
time all such bowldery places will be forest clad.
GLACIATED SOILS.
Where, as is usually the case, the ground left bare by the retreat of
the ice is occupied by occasional large stones which are extensively
mingled with gravel, clay, and sand, all left compactly huddled together
as they fell from the melting ice, the rocky material is very quickly con-
verted into soil. At first, owing to the lack of vegetable matter, it will
not 8upi)ort flowering plants, as we may see by examining the earth left
bare wherever in an artificial way considerable areas of these bowldery
clays are exposed, as, for instance, in pits whence materials have been
taken for road repairs or in the heaps thrown out from beneath the sur-
face beside railway cuts. Here again the lichens and mosses, because
of their tiny, easily wafted seeds or spores and their small need of nutri-
ment drawn from the earth, find foothold and prepare the way for the
higher groups of plants, so that in a few years species with strong roots
occupy the area and rapidly mingle organic matter with the mineral
substances and produce a fertile soil. Such glacial till or bowlder clay
soils commonly have a remarkable endurance to cropping, for the reason
that, being largely composed of rocky fragments, the process of decay
which goes on ui)on these bits constantly yields to plants the ashy
mat4'rials they need, the very substances, indeed, which the process of
cropping tends to ta.ke away from the soil. The main difficulty with
soils found on the till or bowlder clay is that the material is generally
rather impervious to water, and the roots of the plants are not able to
penetrate the dense mass. Moreover, they are commonly filled with
large bowlders, which impede the plow and are often so numerous and
of such great size that it is not profitable to remove them. Yet the
greater part of the tilled land of New England, Canada, northern
Britain, and much of that of the northern parts of Europe has been
8HALEB.] VARIETIES OF GLACIAL SOILS. 237
won from these bowlder-covered fields. The farmers heap the stone in
great walls or upon the surface of the bare rocks; or where the erratics
are too largo to be readily moved tliey excavate a pit beside each one
and so provide it with a place of burial so deep that the plow will not
touch its top. In l^ew England it is probable that more labor has been
expended in tins tMious tivsk of clearing the bowlders away from the
tilled ground than has been given to the construction of all the roads and
farm buildings of the countiy (see Fig. 2 and PI. xv).
The way in which the pebbles of a glacial soil afford nutriment to
plants through their decomposition may oft^jn be clearly seen in the
stubborn fields where these large erratics abound. Around the base of
these bowlders, which the farmers, on account of their great size, have
been compelled to leave untouched, we may often find a narrow strip of
very fertile earth on which many plants requiring rich feeding flourish
luxuriantly. If the bowlder, as is generally the case, is of some granitic
rock, it slowly decays in the air, and every season sends down to its
base a certain amount of material derived from the crystals of feldspar
and mica, rich in lime, potash, soda, and other important soil ingredi-
ents; this share of fertile substainces which may be shed from a stone
many feet in diameter nourishes the plants which feed in the strip of
earth next the stone. Each pebble in the soil is in a smaller way, but
in proportion to its size and rate of decay, doing the same usefiil work
for plants. On account of their solidity, due to the fact that only the
very enduring stones survived the rough handhug of the ice, they are
rarely riven by the roots; some of these stones are so dense that they
still cany on their surfaces the fine scratchings due to their journey in
the glacier, thus showing that they have not decayed to the depth of
one-fifteenth of an inch in all the time they have been exposed to the
solvent action of the soil. In most districts, however, the greater i)art
of these ice-carved fragments are so far decayed that a portion of their
substance has already become food for plants, and in time they will be
entirely converted to this service.
Where there is clay enough in the glacial waste to retain a share of
the water which comes to the fields, and too much is not retained, the
progress of soil-making is rapid. Where, however, the water either
passes swiftly through the debris or can not find a passage at all the
formation of a fertile layer is much more difficult and in some cases be-
comes impossible. In the district formerly occupied by glaciers are
many fields having one or the other of these hindrances to soil-making.
The washed gravels and sands deposited by the flowing waters during
or just at the close of the glacial occupation of a country are often so
permeable to water that they dry out immediately after a fall of rain.
In this case the roots, except those of strong growing trees, can not get
the humidity they need. Moreover, in the long periods of drought the
vegetable matter which may have become mingled with the earth is so
far exposed to atmospheric action that it can not be i)reserved from
complete decay. Furthermore, the finely divided matter, which alone
238 OEIOIN AND NATUBE OF SOILS.
cau eDter into solution in t)ie water, is constantly being borne down into
tbe deptbs of the earth beyond the reach of the ixyots, cither dissolved
in the rapidly percolating water or carried along in the form of mud iu
the downward-setting subterranean movement. By these actions the
formation of a soil is hindered, and many uf these sandy areas within
the old glacial region are essentially worthless for tillage. (S(>e Fig. 2.)
Excellent instances of sncb soils, which are made unprofitable to agri
culture by the extreme ease with which the rain water pasees through
Till or bowUtr clan. BIrati/ud diifl.
Fm. 2 — SHtloDB Bhuwing the tvaconinioD varlelKsnr glaciiU iloVrllan; a, bBclnnk; A. kIikIhI detri
ttu; c c, flne suiil and clay brought up by uU uhI eirtbwanni. Tbe arroWB ibgir the relatlre |>eT-
DHubiUtr of tbe materials to water.
them, exist in many parts of North America and in Europe in the re-
gions which lie to the soath of the southern line of the gla^sial sheet, or
which lie within the ice-occupied district iu positions where (tands were
accnraulated during the retreat of the great glacier. Thus on the'ialands
of Marthas Vineyard and Nantucket, Massachusetts, south of the most
southern line to wluch the glacial mass appears to have extended, there
are great areas of sand plains composed of debris brought out from
beneath the ice by the subglacial streams of fluid water. The great
plain of Marthas Vineyard occupies an area of about 30,000 acres. The
whole of this district lies in a jmsition where it is near the great
markets. It is free from bowlders, and is thus easily reduced to tillage,
but it has remaine^l since the settlement of the country essentially use-
less to man, and has so little value that it is not deemed worthy of taxa-
tion. The material of which this soil is composed is chemically not un-
suited to the nurture of certain valuable crops, but the mass, owing to
the partial lack of the finely divided materials essential to soils, is so
porous, that all the rain water at once and within a few minutes after
the rain has ceased to fall passes below the level occupied by tlie roots.
Other instances of the same nature occur in Plymouth and Bristol
Counties, Massachusetts, and in the southern part of Long Island, New
York, in New Jersey, as well as elsewhere, wherever the rocks worn by
the glaciers have afforded large quantities of siliceous debris. Where
the material yielded to the wearing action is of a limy or clayey nature
these iilaias formed in front of the ice are often of a more compact
structure, and therefore better suited to the needs of vegetation.
BHAiEE.1 VOLCANIC SOILS. 239
Quite opposite conditions, those in which the water cannot penetrate
the soil because of the amount of clay it contains and its exceeding
coR^jl^tness, lead also to an arrest in the process of soil-making. In
this class of cases the roots of the plants And difficulty in penetrating
the tough foundation, and so the area is generally given over to the
mosses, which, owing to the spongy nature of their growth, retain yet
more water, and so the area, unless steeply inclined, is reduced to the
state of a swamp. Now and then some water-loving plant of the
higher orders of vegetation may be able to strike its strong roots
through the peaty swamp material and derive some nutriment firom the
surfaceof the clay beneath. Generally, however, they content themselves
with the little mineral matter which the bog earth contains and which
has been brought to it by streams which flow into the morass from the
neighboring dry land.
Although the conditions of soil-making in glaciated countries are dif-
ficult, the great invading armies of plants which hurried into those
regions as the ice went away have in a wonderful manner subdued the
stubborn fields and covered them with a coating of vegetation which is
on the whole very well fitted for the uses of man. The soils of these
regions have been the nurseries of our race. The Aryan folk, accord-
ing to the opinion of those who have most attentively studied their un-
written history, appear to have attained their character in the glaci-
ated districts in and about the peninsula of Norway and Sweden. Their
name signifies plowman, and they were probably the first people who
used this instrument on the stubborn bowlder-set fields of that part of
Europe; perhaps, indeed, the first to nurture the earth with the aid of
the plow. Their descendants in Scotland, northern and central Eng-
land, and by far the larger part of North America which lies north of
the Potomac, the Ohio, and the Missouri, have dwelt on debris of gla-
cial origin. The soils of these once ice-ridden fields are rarely of great
natural fertility, but with labor and care they generally afford a toler-
ably certain return to the husbandman and endure very well the tax he
puts upon them.
VOLCANIC SOILS.
We now turn to the conditions which control the production of soils
on rocks which have been formed on the surface of the land by volcanic
action. These fields, though occupying a smaller area than those
which have been deprived of their vegetable coating by glaciers, are
much more widely disseminated over the earth. While the glaciated
districts are confined to high latitudes and to certain elevated regions
near the equator, volcanic outflows may occur in all parts of the conti-
nents, though they are usually limited to the districts which are or
were at the time of the igneous activity near the sea. Although these
fields covered with rock which was once molten are widely scattered
and are usually of small area, some of them occupy regions of thou-
240 ORIGIN AND NATURE OF SOILS.
sands of square miles in extent. In the aggregate they probably
amount to near the thirtieth part of all the dry lauds and include
some of the most sterile as well as some of the most fruitM piftrts
of the earth. The region about Naples and that of the volcanic district
of central France and parts of the Sandwich Islands afford types of ex-
cellent soils formed on these volcanic materials; while in each of these
districts, as well as in the extensive lava fields of the cordilleras of
North America, other plains overlaid by lava beds are examples of the
infertility which may come from volcanic action (see PI. xxi).
The solid matter which a volcano throws out upon the surface of the
earth may be in either of two states. It may assume the form of fluid
lava, which flows over the surface in the manner of streams, filling and
clogging the original river or torrent valleys, or, in rarer cases, covering
the whole surface of the area in which the outbreak occurs with a vast
sheet of molten rock; or the molten matter may be blown to fragments
termed ashes by the energy of ttie dilating steam escaping during the
eruption; these comminuted bits of lava, which solidify as they fall
through the air, often cover the earth with a deep coating like fine gravel
or sand. In most cases the flow of lava from a volc/auo is limited to a
few streams which rarely in any one eruption exceed half a dozen square
miles in extent; but it sometimes happens that the escape of lava is not
from the tube-like orifice of an ordinary crater, but the mass of fluid
will pour forth from a long rent in the earth. In this case the volume
of the ejection may be vastly greater and the tide of molten matter
may spread over an area of many thousand square miles. Thus in
Oregon and Washington there is a district containing not less than
100,000 square imles of territory mainly covered by vast sheets of lava,
the product of successive eruptions which appear to have broken forth
from extended fissures. In eastern Europe, in southern India, and
elsewhere there are similar districts of vast extent. In the region of
the Deccan, in southern Hindostan, these sheets of lava have an aggre-
gate depth of many thousand feet and form the elevated table land of
that name (see Fig. 3 and PI. xvii).
The comminuted lava which is blown to fragments by the explosion
of the steam it contains is scattered farther than the lava flows and
often covers the surfa^ce of the earth to a depth sufficient to place the
original soil beyond the reach of plant roots. So widely is this ashy
matter distributed and so vast is it in amount that as a means of destroy-
ing the vegetation of the earth it must be regarded as more devastating
than lava flows. In the great eruptions of the volcanoes of the Malayan
Archijielago which have occurred within the last 120 years the total
amount of this pulverized lava which has been hurled into the air and
fallen upon the land or sea may safely be estimated at not less than
100 cubic miles, or enough to cover the area of a district the size of the
State of Massachusetts with a layer over 6 feet deep. It is not improb-
able that the total amount of this earthy matter poured /orth from the
«■!
SOIL-MAKING ON VOLCANIC E0CK8.
241
Javanese voIcoDoeB during that time lias been as mucli as 200 cubic
miles. On tlie surfa^^e of the earth it is jterliaps Bufe tu say that in the
average each year sees the soil destroyed or deeply buried over a region
of some thousands of square miles in area by the action of these volcanic
products.
• of > district when
■uppoAed orlgiiiAl Bi
, The upper flpin
Ir fins Iwve been loug extinct.
The 8t«p8 by which the vegetation regains its possession of the sur-
face covered by volcanic ejections and proceeds to remake the soil are
essentially like those by which it regains its place in districts from
which it was expelled by glaciatlon, but the details of the process vary
in some iutereating features. When the covering is of volcanic ashes
the etft^t upon the vegetation depends upon the thickness of the sheet.
Ill all parts of the field, except upou the flanks of the volcauic cone
itself, this comminuted rock comes to the earth in a cooled stat«, having
disx>ersed its heat iu the lengthened journey through the atmosphere.
In many cases the fragments are driven upward to the height of fit>m
7 to 10 miles, and it is some hours before they find their way to the
earth. Near the cone and upon its sides there are often heavy rains
of heated water which efTectually destroy the plants and seeds of vege-
tation, so that the country is completely sterilized. A little farther
12 OEOL 16
I
242 ORIGIN AND NATURE OF SOILS.
away these torrential rains are not so hot as to destroy life, and there
we often find the old soil buried beneath the ash shower, but in other
features essentially unchanged (see PI. xix).
It is characteristic of volcanic ash that it is generally a very light sub-
stance and the particles do not cohere with one another, at least until
they are considerably changed by the agents of decay. They are like
the sands which lie on seashores or in dunes. Their lightness is due to
the fact that the bits enclose blebs of air, which are often so numerous
that the fragments will float in water. Under the influence of rain
water the ash easily slips down the steeper slopes on which it lies and
much of it goes away through the rivers to the sea. That which re-
mains, provided the average thickness be not more than 3 feet, washes
down into the vaDeys, leaving here and there exx)osed patches of the
original soil, with the plants, or at least their seeds, essentially un-
harmed. These remnants of vegetation serve as colonies, whence the
organic life spreads over the sterilized fields. The process of this
extension takes place at rates varying with the nature of the ash bed.
Where the material is of a coarse nature, the fragments of the average
size of a pea, the deposit may long resist the advance of vegetation, for
rain goes through it as through a sieve and plants which depend upon
their roots for sustenance find it too dry for their needs; the result is
that for a time the lichens alone can maintain a place upon the ground.
In most cases, however, the fragments of which these ash beds are
formed are easily decomposed. Cooling rapidly from the state of
fluid rock, they are often as frail as Prince Rupert drops and are broken
to bits by the weight of the sui)erincumbent materials or by the changes
of temperature in the seasonal variations of heat. Moreover, their
chemical nature favors decay. At first sight the material of which
they are composed api)ears to be a dark-colored glass, but though
ghissy in its general character it usually contains a good deal of lime,
potash, soda, and iron, substances which greatly promote the action of
the agents of decay. The result is that within a score of years this
ashy matter has become compact enough to retain a share of the rain
water, and its materials are sufficiently decayed to fit the field it covers
for the growth of a tolerably luxuriant vegetation. When the ash is
inore finely dividexl, with its particles of the size of ordinary sand, the
water is sufficiently retained and in a few years the plants may do their
usual work of renewing the soil-coating.
So speedy is the decay of this volcanic ash in all countries where
there is a fairly abundant rainfall that the material usually cements
together by the partial decay of its fragments, forming the variety of
soft rock known as tuff. This consolidation goes on most rai)idly where
the divided matter falls into a basin containing water, as a lake or the
sea, but it occurs in these cases when the material becomes sufficiently
close of texture to hold rain water in a i>ermancnt manner. In any case,
when the mineral matter next to the surfiice has been mingled with
BBALBB] EFFECTS OF VOLCANIC ASH ON SOILS. 243
plant mold, an always happens in rainy districts, these ash beds make
good soils and some of them are of admirable fertility. The variation
in their fitness for the use of plants dex)ends on the proportion of the
various substances which the lava contains. The range in this regard
is very great. Some lavas are mainly composed of mineral species like
silica and iron, which are relatively of little use to plants; others
abound in the elements which most promote the growth of vegetation.
Even from the same volcano there may be ejections which at one time
a£ford lavas and ashes well suited for soil-making and at others produce
ejections which are not well adapted for this end. In general, however,
the most fertile soils of volcanic districts, and indeed some of the most
productive in the world, are in these ash-covered fields. In the region
about Naples, where the ashes of Vesuvius and other volcanoes of the
district which at various times in the last 2,000 years have been in
eruption have covered the surface to a great depth, the earth richly
repays the husbandman for his labor.
In the great outbreak of Vesuvius in the year 79 of our era, a sheet
of ashes covered the country over a radius of 20 miles from the crater
to an average depth of probably from nine to ten feet, yet the tillage
of the country seems not to have been seriously interrupted. In fact,
when the ash is of a tolerably fine grain and composed of easily decom-
poser! rock rich in mineral materials, such as are required by plants,
the effect of the downfall during an eruption may be to fertilize the
field upon which it comes. Looking upon the surface of a cultivated
district which has just received such a shower from a neighboring vol-
cano the appearance is that of utter ruin and desolation. The earth is
smothered beneath the blackish mass of powdered rock which often
levels over the walls and fences and mantles the roofs like the snow
after a great winter's storm. The material seems the very image of
sterility, and if it were an unprecedented visitation the people might
abandon their fields in despair, but experience has taught them that a
little time will return them a frultiul earth. The ashes, at first very
open textured, settle down into a compact mass or are swept away
by the rain, and when the sheet has settled so that it is not over a foot or
so deex) the farmer can by plowing or spading often begin to crop it
again in the very year in which it falls. In a short time the mass may
be better soil than that which was buried, for the older layer has ordi-
narily been somewhat exhausted by tillage. Owing to the frequent
and usually thin falls of volcanic ash the region about Naples has had the
fertility of its soils maintained better and at less cost to the tillers than
those of most regions which are exempt from such visitations. The
same is the case with the volcanic districts of the Javanese Archipelego,
where these ash falls have been greater in amount than in any other
known district of the world. Very few areas are thought to have been
permanently made desolate by these showers of comminuted lava; even
244 ORIGIN AND NATURE OF SOILS.
where the immediate result has been calamitoas, the final result is
usually not evil.
The process of soil restoration on the lava wliich flows from the vol-
canic vent over the surface of the earth is usually much slower and
more ineffective than in the case of the areas covered by the layer of
ashes. When the lava stream or sheet has any considerable thickness
it retains a share of its heat for many years after the mass has ceased
to flow; while it is cooling the plants have no chance to obtain a foot-
hold on its surface. Long after the outer part has acquired the tem-
perature of the air, the inner i)ortion8 of the lava retain a great deal of
heat; this causes every deep fissure to send forth an acid steam which
is very deadly to vegetation. If the lava flow is a hundred feet in
depth, as is not infrequently the case, it may be centuries before the
temperature permits the sprouting of seeds upon it. The conditions of
the lava surface when the mass has cooled to the point where plants
can begin their work of soil-making differs greatly according to the
mineralogical and chemical nature of the rock of which it is composed.
In many cases, notably in the Vesuvian district, the rock is easily bro-
ken up by atmospheric action and soon becomes covered by a layer of
debris. Generally the contraction of the rock, which shrinks much on
cooling, leads to the formation of very numerous crevices, extending
downward some distance from the surface; into these crevices and also
into the irregularities of the lava plain produced by the "roping" of the
lava while it flowed, the rock detritus gathers (see Pis. xx and xxi).
The first plants to take a hold upon the rock are usually the lichens.
Their waste, mingled with the decaying lava, soon affords the beginning
of a soil in the crevices and depressions. In these vantage places the
higher flowering plants find root and extend the field fitted for their
needs in substantially the same manner that we have noted when they
operate on a country from which the ice of a glacial period has just
passed away.
The rate at which soils are formed on the surface of lava is, as above
remarked, dependent on the mineral nature of the deposit, and this
varies greatly in different volcanic regions, and even in the case of the
same volcano in flows which occur at different times. Thus on the isl-
and of Ischia the vast flow of lava from one of the several craters which
spread such wide destruction that the Syi-acusan colony was abandoned
in the fourth century B. C, the rock has remained for more than 2,000
years but little affected by decay. Only here and there have the labo-
rious islanders succeeded in gathering enough soil together to maintain
their plantations of vines. This soil, though very scanty in amount, is
of surprising fertility. Many native plants attain to such a luxuriance
of growth that at first sight they often defy recognition. While these
Ischian volcanoes have produced very enduring lavas which have been
little changed in twenty centuries, several of the effiisions from Vesuvius
of comparatively recent date have decomposed with relative rapidity,
SHALKR.] ORIGIN OF COASTAL DEPOSITS. 245
forming tolerably deep soils. The rate of decay which permits the
formation of soils on lavas is to a great extent determined by the rain-
fall of the country in which they lie. Thus, in the arid lands of the Cor-
dilleras, the lavas of volcanoes long extinct are generally soilless, while
those of the relatively well watered country of the upper Missouri,
though not more ancient, have in many places produced an abundant
soil.
SOILS OF NEWLY ELEVATED OCEAN BOTTOMS.
The foregoing account of the processes of soil formation on the land
areas, where the accidents of frost and fire or those arising from land
slides or avalanches have deprived the surface of its natural covering,
shows us how swift and eflfective are the means whereby organic life
wins its way back to the regions from which it has been rudely dis-
possessed. We have next to consider the rather different conditions at-
tending the formation of soils on lands which have newly emerged from
beneath the sea. The instances in which this process can be observed are
rare and have never been adequately recorded. So gradual in most in-
stances is the speed of uprising that the land gains on the sea at the rate
of only a foot or two in a century and the soil gradually extends so as
to cover the emerged surface. It is, however, tolerably certain that in
many of these changes of level the upward movement takes place rather
swiftly, so that in a few years a large area of land is left dry and thus
subjected to the actions which make soils. Thus, at the close of the
last glacial period a large part of the northern and eastern region of
this continent, and probably the neighboring portions of Eurox>e, were
below the level of the sea, from which they emerged in an upward move-
ment, evidently of a rapid nature. There is reason to believe that the
uprising in the region along the New England coast was at the rate of
as much as a hundred feet of altitude in a year,^ the result necessarily
being that a large extent of country newly won from the sea was open
to the incursions of plants. To conceive the way in which they won a
foothold on this surface and reduced it to the state of soil it is necessary
to consider the conditions of the sea floor in the shallows next the shores
of the continents, for it is mainly from such ocean bottoms that the new
lands are won by the process of continental upgrowth.
The bottom of the sea next the continentsU shores is usually, to a great
extent and to a great depth, composed of matter which has been re-
moved from the land by rivers and waves and distributed over the bot-
tom by the action of the tides. Along the Atlantic coast of Europe
and North America this deposit forms a broad fringe of shallows the
surface of which slopes gradually from the shores, generally at the rate
of 5 or 10 feet of descent to the mile, until it attains a depth of about 500
feet. Then it descends rather suddenly into deep water. Along with
the material swept from the land, sand and mud derived from ancient
1 See Eighth Ana. Rep. of Piiector of U. S. GooL Hurrej, 188^'87, p. 987 et aeq.
246 ORIGIN AND NATURE OP SOILS.
soil which -the streams have carried out from the interior of lands or
waves have removed from the coast Une, there is mingled a large amount
of organic matter derived from the decay of animals and plants which
dwell on the sea and, dying there, give their remains to the bottom.
Wherever this detritus is very rich in Ume, as is the case in the por-
tions of the sea floor on which shell-fish or corals abound, the deposits
are apt to consolidate as they are formed, making loose-textured lime-
stones, generaUy with more or less admixture of sandy matter. Where
mud prevails the resulting beds are of a clayey nature and do not com-
monly become more compact than ordinary brick clays. Where, as
is commonly the case, the materials on the floor are mainly sandy, the
strata which they build remain in an incoherent state, for it is not until
they have undergone considerable changes that pure sands will firmly
cohere.
In most cases all materials laid down on the sea floor have in them a
mixture of ingredients well suited to the formation of tolerably fertile
soils. These they derive in the main, or in most instances, altogether
from the organic materials which they contain. Wherever by some
chance we have had lifted into the air a portion of the ocean floor which
was covered with siliceous sand, it remains for a long time sterile. Such
instances of arenaceous sea bottoms are fortunately rare, and when the
coptinental fringe or shelf rises into the atmosphere there usually is
euoy^h fertile material in the mass to support plant life, and generally
the mineral matter is suited for the maintenance of a good soil. More-
over, the substances not being much consolidated, there are no such
hindrances to their appropriation by plants as exists in the older and
more consolidated rocks that underlie the whole earth and appear at
or near the surface over the greater part of its area. Except when
composed of Umestone the newly emerged sea floors generally have a
composition which offers no resistance to the penetration of plant roots.
We may obtain some imperfect idea of the process by which land
newly risen from the sea becomes occupied by vegetation by exam-
ining the areas where the tides have been diked out from a territory
which they have been accustomed to overflow, and the area of sand or
mud flats thus opened to land vegetation. We note that the surface is
at once seized upon by the various spore-bearing cryptogamous plants,
such as the lichens and mosses, which make a whitish or yellowish crust
on the surface. After a short time, when these lowly forms have made
a layer of intermingled mineral and organic matter perhaps a third of
an inch thick, higher sx)ecieB of slender and lowly habit find a lodgment,
and by sending their roots a little farther into the earth deepen the
nascent soil. In their turn come the sturdier plants which demand
more nutriment, and in the course of a few years the earth is fit for the
occupancy of forest trees.
In the great plain land of the Southern States of this Union, includ-
8HALHI.) CORAL BEEF SOILS. 247
ing the eastern parts of Virginia, the Oarolinas, Gteorgia, the whole of
Florida, and the fringe of lowlands bordering the Gnlf of Mexico and
the Lower Mississippi, in general all the surface of the region below the
level of 500 feet in altitude, we have a district in which the land has
recently arisen from the waters of the ocean and become soil covered.
In all the lower lying parts of this vast area, say the ground within
300 feet of the sea level, the emergence is so recent that we can still
perceive that the surface usually has the peculiar gently undulating
shape which is characteristic of the sea-floor. In this part of the coun-
try it is interesting to observe the process of soil-making on the diflTerent
classes of materials— clays, sands, limestones, or various admixtures of
these substances. We note in the first place that the soil on this dis-
trict is generally thin, a fact which goes to show that unlike the deep
rich earths of other and higher lying regions, it has not been a long time
in the process of construction. Then we may trace the varying degree
of retardation which the soil-making process has met and from the in-
quiry learn among other things how slight differences in the conditions
of the rock may produce very important variations in the results.
One of the best places to study these southern soils is in Florida, for
in that State the surface varies but little in height or in climate, and
the condition of the rainfall to which it is exposed and the profound
differences in soil are due mainly to variations in the nature of the
underlying rock. In the region of the Keys we have that rare form of
coast deposits consisting of coralline limestone; the islands being in
fact ancient reefs which have been elevated to the height of 20 to 40
feet above their original position. The material of which they are
made is nearly pure limestone, derived from the remains of corals and
moUusks and other lime-decreting organisms which lived on the reef
while it was below the level of the sea. There is in the mass a little
volcanic ash brought to the region by ocean currents from remote vol-
canoes and a small admixture of various other substances, such as
phosphorus from skeletons of fishes and crustaceans, a little potash,
soda, iron, and other mineral matters taken from the sea by marine
animals and plants and built as fossils into the dex)osits of the sea floor.
The material is a very good source for a supply of the mineral elements
necessary to insure fertility in a soil. The rainfall is great and the
temperature is tropical, so that the vegetation, when it finds a foothold,
is very luxuriant. But a large part of the surface of these reefs remains
singularly destitute of soil; here and there only do we find a patch of
detritus which is deep enough for ordinary tillage, and this only where
the slope of the ground has preserved in a small area the accumulation
of d6bris which has been produced over a much larger neighboring
surface.
The cause of this paucity of soil in a region where we should expect
to find an abundant deposit is interesting, and it leads us to discern a
certain feature of the earth's history which has generally escaped atteu-
248 ORIGIN AND NATURE OF SOILS.
tion. There can be no doubt that soil-making material of fertile quality
is produced on these reefs with great rapidity. The little there is of
it in the crannies and low places of the rocks bears a luxuriant foliage.
What, then, is the reason for the small amount of the accumulation f
The explanation is to be found in the remarkable purity and solubility
of the lime rock which forms the Keys. It is evident that this rock is
rapidly wearing away; it is everywhere channeled by sink -holes and
caverns, and the water which flows, from them is heavily charged with
limy matter. The fact is, that as fast as the rock decomposes and the
bits are appropriated to the soil they dissolve in the water and are
returned to the sea in a state of solution. The result is, that it is im-
X)ossible to keep the mineral elements in sufilcient proportion in the
mixture with decayed vegetable matter to form a continuous soil coat-
ing. It is only where the dex5omposed rock is washed from a considera-
ble area of the surface into some cavity that a soil of ordinary thickness
can be formed. If there were 10 or 20 per cent of ordinary sand in the
limestone there would be a solid basis tor the soil which would serve to
inclose the vegetable matter, or if the region were in a moist, cool climate
the slower decay of the limestone bits would still enable them to remain
to nourish the plants. In such a climate in the winter season there
would be no process of solution going on, and the rain water being less
heated the solvent action would be much le^s considerable than in the
summer season, but in this frostless land, where the rainfall amounts to
as much as 90 inches per annum, all the bits of stone which should go
to form a soil are taken into the water and borne away. We shall here-
after have occasion to note that in other limestone districts the excessive
solubility of the mineral matter, as well as its occasional insolubility,
may alike interfere with the formation of soils.
In the everglade country of Florida we have another type of soils
which, though in part coming under the head of swamp deposits, de-
serve mention here, though they must be again referred to in a later
section of this report. In the everglades the water on the eastern side
and in the central portions of that remarkable region rises in the late
summer and autumn until it forms a vast lake covering almost the whole
area. When in this extended form this water absorbs a gre^it deal of
lim^. from the rocks which it covers. When these waters dry away in
the winter and spring they leave a thin coating of limy mud intermingled
with leaves on the surface of the bared earth. This, accumulating from
year to year, forms a peculiarly black dense soil, rich in lime and other
elements needed by plants, and therefore of remarkable fertility. Un-
fortunately, only a small part of this excellent soil-making material is
retained on the land; the greater part escapes to the sea through the
streams which drain the everglade country.
In the central and northern parts of Florida, there are extensive
areas occupied by sands which have evidently been subjected to the
action of strong marine currents, and in this manner have had the finer
8HALBB.] SOILS OF THE SOUTHERN PLAIN. 249
materials^ such as clay, removed from them. Here the soils are very
thin because the plants find little mineral nutriment. The siliceous
element is, it is true, essential to plants, but they can not support them-
selves on that alone. In such places we find scrubby pine trees rising
from an earth which bears little other vegetation. The roots of these
trees strike deep into the earth and thus, occupying a large space,
gather the little they need for their scanty growth; but the ordinary
annual and herbaceous plants can not endure the sterile conditions.
Moreover, the soil is not only lean, but the rain which falls ui)on it
quickly percolates, carrying with it to a considerable depth nearly all
the soluble material which might be useful to plants and leaving in
the rainless season no water near the surface. The conditions of this
region as far as its soil is concerned remind us of those which we have
noted as occurring in the washed sands of the glaciated part of the
world. In both we have the surface covered by porous sands which, by
permitting the speedy and complete passage of the water, hinder the
work of making the earth a fit place for plants.
In a large part of the southern lowlands the evils arising from the
sandy nature and excessive i)overty of the soil are considerable. In
most districts, however, there is a sufficient admixture of clay to make
it possible for the forests and lower growths to convert the mineral
matter into fairly good soils. It is probable that the whole region was
covered by a growth of flowering plants almost at once after its last
uplifting above the sea; as yet, however, the work of soil-making is
much less advanced than it is in the higher country, where the surface
of the earth has been above the ocean many times as long as the south-
ern coastal plain.
We have now considered the processes of soil formation where the
surface of the earth is newly exposed to the conditions which create
this covering. We shall now have to undertake a more detailed study
of a typical soil with a view to acquiring a general idea of what we may
term its physiology; that is, the way in which it is maintained in its
essential functions and the manner in which the various processes of a
geologic nature which go on within it are accomplished. In this task
we shall consider Uttle of the chemical work which is done in this
stratum, for the reason that such problems for their understanding de-
mand a good deal of technical knowledge and come rather more in the
special domain of chemical than within the limits of geological science.
For the purpose of our ftLcther inquiry the reader should keep in
mind the general aspect of at least two classes of soils which are
famUiar to most persons or may readily be seen in all parts of this
country save those which have been extremely affected by glaciation,
viz, those derived from the decay of the rocks which are immediately
below the soil and those which have been brought into the region by
rivers and deposited in alluvial plains. It is well also to know some-
thing of the asx>ect of the glacial and volcanic ash soils, but a sufficient
250 ORIGIN AND NATURE OP SOILS.
idea of these may, perhaps, be gained from the flgures wliich aceom-
pany this text.
PHYSIOLOGY OP SOILS.
So far we have been considering those very general features concern-
ing the origin and distribution of soils which we may term their physi-
ography. We shall now proceed to examine into the details of certain
processes by which soUs come to serve the needs of plants, the ways in
which their fertility is maintained, and in general their relations to
geological actions. These inquiries should be begun upon that type
of soils which occurs on the older part of the land surfaces, on those
portions of the continents which for many geological i)eriod8 have been
above the level of the sea, for there alone can, we trace in a satisfactory
way the successive steps in the history of a soil. After learning the
history of such a typical area we may then compare the deposit with
the less normal forms, some of which we have sketched in the preceding
pages.
This detailed study of the physiology of soils may best be approached
through a consideration of the forces which operate in the production
of such deposits. It is easily seen that all soils represent the applica-
tion of a certain amount pf energy, which diversely applied constitutes
in the aggregate a vast sum. Soils are composed in part of rocky mat-
ter which has been broken into bits and mingled with organic matter.
The stony material has been much aflfec^ted by chemical agents which
have produced an evident decay, and this also indicates the application
of energy. The vegetable and animal waste, which is as necessary in a
soil as is the mineral matter it contains, owes its existence to the sx>ecial
application of energy which brought the elements of the plants from the
soil and the air into the combinations of life which contribute so much
to the soil. We shall now inquire as to the source and methods of ap-
plication of these diverse modes of action.
It does not require much observation to show us that the greater
part of the forces wliich operate on the soil are derived from the sun.
It is clearly solar heat which causes all the movements of animal and
vegetable life; and all the growth of roots, stems, and leaves is evidently
due to the warmth of the growing season. In our latitudes, when the
sun moves away to the south, the share of its radiation to our land is
so far diminished that the growth of plants is arrested and the ground is
commonly frozen, so that all the operations which lead to soil-making are
for the time suspended. When the great source of power rises higher in
the springtime, all the machinery of organic life and chemical change in
the superficial parts of the earth renews its activity. Thus the depend-
ence of the soil upon the solar heat for all the actions connected with
seasonal temperature is absolute.
Slightly more extended ex)n8iderations show us that the rainfall which
comes to any country is also due to the heat of the sun. The waters of
sHAiJm.) EFFECTS OF SNOW ON SOIL. 251
the sea, warmed by the rays from the solar center, ascend as vapor.
Their upward movement is due to the energy which is thus applied.
When these vax)ors attain the higher regions of the atmosphere, they
are drifted by the winds, which owe their motion also to the same source
of heat, and pass from the oceanic areas to the land, where, if not before
precipitated, the store of moisture descends in the form of rain or snow.
Falling upon the earth, this water imported from the sea becomes a part
of the chain of causation which is in various ways related to the forma-
tion or destruction of soils. The rdle of actions is extended and varied,
but it is easily to be understood, and it constitutes one of the most
charming series of phenomena which the earth exhibits to the inquirer.
When the water which falls from the clouds comes down in the form
of snow it descends gently upon the earth and accumulates in the fiunil-
iar covering which winter lays upon lands outside of the torrid zone. At
first and for the duration, of a single season the effect of the snowfall is
advantageous to the soil, for it prevents the deeper freezing which is
hkely to take place when the earth lacks this snow blanket. The frost
which has seized upon the ground before the snow falls is melted by the
heat ascending from the deeper earth. Often the warmth thus induced
in the soil is sufficient to start the lesser plants into life and even to
stimulate into a certain activity the roots of trees whose trunks and
branches are in the cold upper air. It has often been observed that in
frigid countries, where the snowfall is ^ deex) that it does not melt
away until the summer warmth is well affirmed, the small flowering
plants will blossom beneath the frozen sheet. Released by the action
of the snow covering from the bondage of frost, the soil is free to undergo
the manifold chemical changes which are necessary to bring the mineral
part of its constituents into the state in which they can serve for plant
food. Thus the season of preparation of the soil for the demand which
the roots make u|)on it is, through the action of the snow covering, very
much prolonged, and the preparation of nutritious matter takes place at
a time when there is littleor no drain made upon it. The advantage of this
condition, brought about by the snow blanket, is recognized in the adage,
" Snow is the poor man's manure.'' In this x)hrase farmers have embod-
ied their sound observation as to the effect on the open soil which the
winter's mantle insures.
If the snow vanishes, as it usually does during the summer season,
the effect of the accumulation is altogether beneficial. If, however, the
covering is so thick that it outlasts the time of warmth, so that the layer
thickens from year to year, the mass soon begins to move downward
toward the sea. Even in a single winter snow which is deposited on a
steep slope takes on a glacial movement and creeps toward the base of
the inclination, carrying with it the loose materials which lie upon the
surface. Where this action is continued and intensified the effect is, as
we have already noted, the inevitable destruction of the soil. Tliis
glacial movement acts upon the earth's surface as a rasp, gradually wear-
252 ORIGIN AND NATURE OF SOILS.
ing away at first the incoherent materials which lie ax)on tlie more solid
ground and afterwards the firmer rocks, which it may erode to a great
depth. When the ice sheet disapi)ear8 it leaves the land bestrewn with
debris of various kinds. The old valleys by which the rain waters were
discharged are greatly changed in form, so that, as in the boreal parts
of North America, the originally well drained surface is to a great ex-
tent occupied by lakes and swamps or by sandy and rocky fields, on
which the soil-making processes find it difficult to accomplish their work
in a way to serve the interests of higher life. The sharp contrasts be-
tween the conditions which are brought about, on the one hand by a
temporary covering of snow and ice and on the other hand by the more
continuous coating of a glacial sheet, affords us one of the many instances
in which slight differences in the mode of natural action produce on the
soil as elsewhere the widest variation in effect (see Pis, iv and xvi).
There are only a few places within the limits of the United States where
glacial work on a considerable scale can now be observed, and these are
all situated in the western portion of the Gordilleran region. It may
therefore be worth while to note certain familiar examples of the rub-
bing action which even an ordinary winter's snow sheet has upon steeply
inclined portions of the earth, where it lies as a thick covering. If we
visit a hillside of moderate steepness at a time when a thick coating of
winter's snow has just been cleared away we may note in the attitude
of sticks and other dead bits of wood that the surface has been subjected
to a certain amount of rubbing which has urged the fragments down
the hill. Thus we not uncommonly find where a branch, fallen from a
tree, has in its downward movement encountered some obstacle, such
as the trunk of a tree, around which the bough has bent in the manner
of a bow, the two ends being dragged some distance down the hill.
Occasionally we can note where stones, sometimes as large as a man's
head, have been pushed down the hill, leaving a slight groove to mark
the energy with which they have been urged forward in their move-
ment. Sometimes, though rarely, this downward movement of the
winter's snow is sufficient to disrupt small stone columns which have
been constructed upon steep hillsides. Thus, in the cemetery in Au-
gusta, Maine, where the monuments have been placed on a steep hill-
side where the snow deeply accumulates, it has more than once hap-
pened that the slow, creeping glacial movement has broken off stout
tombstones and iron fences which surround graves. This action has
taken place, not in the manner of an avalanche, but with a slow motion
which carried the disrupted object-s only a few feet from their original
I>osition. In this way we see how, even in regions where true perma-
nent glaciers are unknown, the snows of winter give us a very clear
semblance of their action.
On the greater part of the earth the rainfall comes in the form of
flood water or ordinary rain, and as such journeys downward to the
sea. To understand the function of this fluid the observer should trace
BHALEB.] ACTION OF RAIN ON SOIL. 253
its action from the place where it fell upon the earth to that where it
reentered the ocean. This, at least in a general way, I shall now en-
deavor to do. When the drops of water strike the surface we observe
that they fall with a certain amount of force ; this energy is immediately
due to gravitation, but it is remotely owing to the sun's heat, which
uiilifted the water to the clouds whence it falls. This blow of the rain-
drop may seem of slight imiK)rtance, but it is really of great moment.
If we watch any newly plowed field where it is exx)osed to a heavy rain
we notice that the drops cut the clods to pieces in a rapid manner.
After a single shower following the work of the plow we may here and
there find where a flat pebble or a x)otsherd has protected the earth from
the assault of the descending water. Each of these sheltering bits rests
upon the top of a little column of soil, which may be an inch in height.
In many countries, as for instance in Colorado, where there are exten-
sive areas of soft rock, with occasional hard patches of material con-
tained in their beds, we find that this phenomenon is shown on a large
scale, the columns often being 20 feet or more in height, each capped
by the protecting stone which has preserved its pedei^tal from the stroke
of the raindrop.
It is to the disrupting effect of this reiterated dropping of the rain
that we must in the main attribute the rapid washing away of soils which
are by tillage much exposed to the direct attack of storm water. K
there were no natural protection against this the soils would be in a
geologically brief time entirely swept away; they would indeed not now
exist as a general coating, but would be limited to certain places of a
swamp-like character into which the detritus from higher lying rocks
would be swept by the floods. From all surfaces of evident slope the
materials would be worn away. Fortunately for the economy of the earth,
a nearly perfect natural protection is afforded by the coating formed by
the stems, branches, and leaves of plants, which along with the debris
from their bodies lying confusedly heaped upon the ground, serves to
protect the earth from the direct action of the falling rain and yields
the water gradually to the under earth.
As soon as the rain drops strike the surface they flow together and
form a thin sheet of water; where the earth is bare of vegetation a part of
the fluid quickly gathers into rills and flows away, rill joining to rill
until considerable streams are formed. On plowed ground this surface
water bears with it a heavy burden of the soil which it conveys away
to the lower lying district and often transports to the greater rivers and
thence to the sea. A large part of this loss of the soil is due to the
admixture of its substance with the water under the action of the fall-
in g raindrop. In a time of heavy rain a field, if it be much incUned in
its surface, will often lose on the average half an inch in depth of its
soil covering by this action. On the other hand, in a forest-clad country
the rain even where it descends in heavy showers forms no sheet of water
upon the surface; it is all absorbed in the forest bed and thus no small
264
ORIGIN AND NATURE OF SOILS.
rivulets result. The water sinks into the sx)ongy coating, and in that
tangle of decaying vegetation it slowly creeps down the declivities until
it is gradually yielded to larger streams, trickling out along their margins
from the mantle of leaves, twigs, and roots which covers the earth per-
haps to the depth of 2 or 3 feet. While on a bared field there may be
two or three rivulets formed in a time of heavy rain on each square yard
of the surface, so that the area is quickly seamed by a labyrinth of little
valleys, in a neighboring district having the same character of soil and
a like inclination of surface, but covered by a virgin forest growth, we
may not find an average of one stream to the square mile. This feature
is illustrated in the a<H3omx)anying diagrams, which are intended to indi-
cate the contnist. , Wliile each of these water ways in the forest is occu-
pied by a j)erennial brook fed from the si>ongy soil, streiim beds on the
tilled land are all dry save when the rain is actually falling (see Fig. 4).
Fio. 4.— Map showing comparative deTolopment of stroam beds in a district when it is forested and
when the wood is romoyod. a, forested state; &, deforested state.
It is very evident that the difference in the amount of energy applied
by the rain to the surface of the earth in these two contrasted conditions
of forest-clad and bare earth is very great Creeping through the inter-
stices of the vegetable coating, rain water may descend the mountain
side through a vertical distance of thousands of feet, moving all the
while so slowly that it does not apply any sensible energy to the soil
covering, while if that surface be deprived of vegetation it may on ac-
count of its swift motion api)ly an intense erosive force to the incoherent
soil.
All that part of the rainfall which flows away over the surface tends
to destroy the soil coating, and, as we have seen, it effiHjtively accom-
plishes this end wherever the earth is not protected by its action. This
surface water, however, represents only a portion of the rainfall; the
remainder enters the earth near where it falls and is thenceforth, until
it is again gathered into the surface waters through the springs,
mainly an agent of soil construction. The proiX)rtion of the under and
surface water, or that which sinks into the ground and that which flows
8HALBB,] ACTION OF GBOUND WATER. 255
away upon it, differs very much according to the physical characteristics
of the district in which it falls. In general, the ground water is pro-
IK)rtionately much greater in amount in those cases where the surface is
forest clad than where it is tilled, for in the woods the earth never be-
comes baked or compact, and, held in the forest sponge, the water has
ample time to penetrate the soil before it escapes to the streams, while
on the bare ground it slips away rapidly toward the sea. It is a familiar
observation that the soil of a tilled field, especially if it be of a clayey
nature, remains quite dry in its under parts even when its surface has
been seamed by a torrential rain. Where the earth is very open text-
ured, as is the case with the washed sands of the glacial districts or of
the similarly sandy and nearly soilless areas of Florida, the water, how-
ever heavy the rainfall, may all immediately penetrate the ground with-
out flowing over its surface. Thus in the glacial sand plains of south-
eastern Massachusetts there are often no traces of stream beds over
di^ricts of many square miles in area. It is evident that no water has
flowed over them since they were formed in the closing stages of the
last ice-time, save perhaps during winter when the soil was firmly frozen.
Where the soil is a dense clay, even though it be covered by primitive
forests, the proportion of the water which enters the earth may not
exceed one- third of the rainfall. On tilled ground the relative amounts
of the under and over water varies exceedingly, in a measure deter-
mined by the character of the rainfall, whether rapid and brief or long
continued and slight. When the surface is of bare rock the amount
of penetrating water is always relatively small in quantity (see Fig. 2).
When the winter's snow remains on the ground throughout the
frigid season and the under earth consequently passes from the frozen
state which it acquired before the snow came down, the melting snows
commonly yield their water to the under soil in a larger measure than
is the case with other forms of rainfall. The snow when it gradually
disappears commonly melts most rapidly upon its contact with the earth,
so that the water retained beneath the remainder of the coatinghasabun-
dant time to filter into the soil. The reader may have noticed that in the
time of snow-melting the layer generally lies ui>on extremely wet earth,
and if the soil be of a clayey nature there may be an almost continuous
sheet of water upon its surface. Thus regions where the snowfiiU is
abundant and persists into the spring-time are apt to get a thorough
soaking of the earth at the time of year when abundant watering is
extremely advantageous to natural as well as to tilled vegetation.
That part of the water which has entered the ground is the efficient
instrument of soil-making. All other processes contributing to this end
depend ui>on its action in an immediate and complete manner. We
shall therefore have to scan the history of ground water in a somewhat
careful way. When the heat of the sun takes the water of the sea into
clouds in the form of vapor the fluid rises in the distilled form; it has
left behind all the mineral substances which were dissolved in it and is
I
256 ORIGIN AND NATURE OF SOILa
in a nearly chemically pore state. There probably remains some trace
of certain dissolved substances, but the quantity of admixture is so small
as to have a scientific interest only and no economic consequence what-
soever. When the vapor is converted into rain, and possibly while it is
still in the diffused form of clouds, the water is in a condition to absorb
into its mass various gases for which it has a physical afi&nity. The
measure of this capacity for taking in gases varies greatly and does
not inmiediately concern our inquiry. It is, however, as we shall see
hereafter, of the utmost consequence that among the gases which this
liquid readily and in large quantities absorbs, is that combination of
oxygen and carbon commonly known as carbonic acid gas (CO^) now
termed by chemists carbonic dioxide. This substance exists in all parts
of the air in proportion to its weight in nearly equal parts. Thus in the
atmosphere through which it passes, the rain has a chance to absorb a
considerable amount of COs before it touches the earth. Snowwater,
because of its frozen state, probably takes in less of this gas and may
enter the earth with comparatively little of the material dissolved in its
mass.
When the water from the clouds, coming either in rain or snow, enters
the earth, it commonly passes through a more or less extensive layer of
organic material in the state of deox)mpo8ition. From this layer it takes
up a yet larger charge of this gas as well as of other materials which are
of importance in its subsequent work. It probably gains from this layer
an additional amountof ammonia and other nitrogenous substances which
it had begun to acquire in its journey through the air, but it notably
increases its store of carbonic dioxide. The quantity of this gas which
water may contain when it Anally enters the true soil is indeed sur-
prising; it may amount to several times the bulk of the fluid.
Now on the presence of this dissolved carbonic acid gas depend some
remarkable effects which water produces on the soil. The most notable
influence of the CO2 contained in the soil-water arises from the singular
increase in the capacity of the fluid for taking substances into solution,
which is afforded by the presence of this gas. Ordinary distilled or
rainwater at the temperatures which prevail on the earth's surface has
very little capacity for taking such mineral matters as abound in ordi-
nary soils into solution; it will take up only a trace of lime carbonate or
lime phosphate or of the ordinary salts of magnesia, iron and a number
of other substances which must be brought into solution before they can
be of use to plants. The charge of CO2 which water may absorb before
it enters the deeper part of the soil increases by some fifty-fold its ca-
pacity for dissolving lime carbonate and manifolds its absorbing iK)wer
in the case of many other substances.
In passing through the layer of vegetable mold and the upper part
of the true soil, in which there is much decaying organic matter as
well as many living roots, the water encounters a set of conditions
which are exactly fitted to provide it with this charge of carbonic dioxide.
In the decay of carbonaceous matter GO3 is generally formed in larger
BBALKE.] FORMATION OF CAVERNS. 257
amountH than any other gas. The reader is [trobably familiar with the
fact that veils and other pits whicit have been simk tlinnigh rich soil
are likely to become filled with this gas, or whiit is (tommonly called
fixed or irrcapirable air. The pi-eseuce of this gas frequently leads to
the death of those who venture iiit^i such excavations without the
simple precatitioQ of testing tlie nature of the air by means of a lighted
caudle lowere^l into the pit. Among the many nice adjustinentH of the
conditions of the earth to the needsof life we must reckon this arrange-
ment by which the soil water absorbs a large part of its charge to tlie
gas which renders it most efficient in its work through the decay of
kindred forms.
It is a charm^t^ristic teature of water that iU* capacity for absorbing
and retaining gase^ rapidly increase:^ with an augmentation of the
pressure u|>on it. This may be Be<'u by observing the action of CO, in
a common glass sijihon charge<l with what is commonly iralhnl soda
water. This fluid consists of ordinary water int^i which the above-
named gas has Ix-en introduced by ]»ri!SKiire. We note that wlitle the
fluid remains tightly inclom'd, the gas is not visible; but on opening
the Rtop-cock tlie gas may be seen i-apidly to sejtarate from the mass
of fluid and form bubbles which rise at once to the surface. If the
FiQ. &,— DUftrain Bhowlog acllon of toil wnirr lu eiMvstlng tavern", a a. Ujitii of liniBntnne. eully
dlHKilTCd In son VBler; b b. sink huloa by whick tho noil wslor eiilers Iho caw, c e. loltlnd ohaftfl
ordamea; d d, horiunital gaUerin. The arch in the middle eutnneeis s uulunl bridge or remuiuit
passage is widened the uprush of the gas will be so rapid and plentiful
that a ^Hirtion of water will be driven out with it. If the escA)>e is made
gradual the giia will be seen to separate bubble after bubble until the
eye readily recognizes the fa4;t that a quantity of tlie 0()t, amounting
in bulk to several times that of the water, has eseaiietl from the vesse-
without sensibly diminishing the quantity of the fluid. By this exi>eri-
ment it is easy to perceive how great an amount of carbonic dioxide
water, under slight pressure, may contain.
When it enters the under earth and passes thence into the subjacent
rock the soil water, provided it courses through limestone, excavates
caverns which are so well known in many parts of this country. The
soil water gathering on the surface, finds its way downward through the
Joints of the rocks which it gradually eidarges, forming a vertical shaft
or dome ; thence it creeps through galleries to its place of discharge into
the open-air rivers of the region in which the cave lies. At the upper
entrance of the cave a fiinnel-like depression is formed, at the bottom of
which there is a shaft which permits the downflow of the water into the
chambers below, (See Fig. 5.) These pits are often very numerous and
12 GEOL 17
258 ORIGIN AND NATIIRK OK SOILS.
Bometimes seriouHly interfere with tlie work of the faniior. If lie le.tves
them oi»en the beasts of liis fields are often killed by fulling into tlie
caverns. If he artiflt^ally cl(»*ea the shafts, water gathers in the basin,
frequently overflowing eonsiderable areas of tilled land. The genenil
asjieet ofthe.se sink boles is sbown in Plate xxii.
When the ground wster enters the depths of the earth it i>aHises into a
realm where, with eacli step of its descent below the surface, it bec4>ineH
liable, especially where the soil is wet^ te be more and more subjected to
heat and pressure; owing to this action it iscoostantly enabled to increase
its charge of the gases, which aid it in dissolving substances of a mineral
nature. Thus when it penetrates the underlying rock, as it ofte,n does
to a considerable depth, the pressure to which it is subjected, duo U> the
column of water above it, materially increases its capacity for dissolring
limestone and other roi^ky matter. When it flows back toward the sur-
face the ])ressure is reduced — it loses a portion of the OOi ; an<l as it held
the mineral matter by virtue of this gaa and in proportion to the quan-
tity wbich it contained, the disMdved substances are in ])art laid down
near the surface of the soil. Tlie importance of this action in bringing
upward to the true soil materials of value, which plants could not obtain
by means of their roots, is doubtless very great (See Fig. 6.)
t te. 9 IHaftnuD (howiuK one of the oondittuiM by whliiti soil water may ]«in^rBti> deojil.r and rnneri^
a* a boiBprlDg. a a, poivns bed at rock; A b, InipcrtiDaa lajran^ c c. fault.
It is to the ceflseless movemenbi of water through the dctrifal coating
of the earth, and the consequent solution and carriage of materials
wbich are brouglit for the needs of plants into i>ositioiis where the roots
can feed upon them, that we owe nmch of the fertility of the earth. It
is therefore desirable to consider another action which, combined with
that just described, still further favors the process of ujtliiting the nu-
trient matter of the earth into the levels where the roots do their appro-
priate tasks. This uplifting effect on the ground water is brought about
by the process of evai>oration. When a soil is fllled with water as it is
aftier a time of heavy rain or meltiug siiow, all the crevices of the mass
i <
i I
n
r
s
i
gHALKB.J EFFECT OF CAPILLARY ATTRACTION. 259
and the spaces between the bits of organic and mineral detritus are
occupied by the solvent fluid which takes into itself a large share of the
soluble matter which the neighboring earth affords. Such a time of
thorough watering is apt to be followed by a season of drought in which
evaporation goes on in a rapid and effective manner; the superficial
portion of the soil water then passes into the state of vapor and disap-
pears in the atmosphere. As the evaporation takes place altogether at
the surface of the earth, the upper layer of soil becoming partly dry,
the spaces between the grains of the material suck up the water from
lower levels of the earth; this in turn evaporates and as it goes off as
vapor it leaves all the mineral matter held in solution as a deposit in
that part of the earth, sometimes sufficient in amount to form a crust.
It may not at first seem clear that the process of vaporizing the sur-
fEfcce water should cause the lower lying fluid to rise to the upper level
of the soil, but the action may be made perfectly clear by remembering
the kindred phenomena exhibited by the wick of a lamp, which draws
up the oil as rapidly as the flame consumes that part of the fluid in the
upper portion of the capillary tubes formed by fibers of which the wick
itself is comiK)sed. Or we may in any tree find a partial illustration of
the same principle; the sap rises because the evaporation from the sur-
face of the buds and leaves calls upon the fluid which is lower in the
plant to supply the place of that which goes away as vapor, so that the
whole structure becomes like a great wick in which the water is grad-
ually drawn upward perhaps hundreds of feet above the reservoir of
the soil. This analogy is satisfactory only in part, for the reason that
at the extremities of the branches where growth is going on a certain
movement of the sap is due to a peculiar action of cells which can not
be here described, but in the body of the trunk the motion is probably
caused by capillary attraction.
The energy of the attraction which the adjacent surfaces of the soil
exercise upon the water may perhaps be more clearly conceived if we
note the fact that if wedges of dry wood be driven into a crevice of a
rock and then be wet, the water will be drawn into the interstices of
the wedge with such energy that a disruptive effect will be produced so
jiowerful that it may rive the tough stone asunder. It is in good part
to this capillary process set in a<;tion by the demand which the roots
make vLpon the soil as well as by the evaporation from its surface, that
we owe the ceaseless to and fro wandering of the earth waters. These
movements enable the fluid to gather into itself a great variety of sub-
stances. In its joumeyings it offers the matters it has dissolved to the
rootlets of plants so that they may select the materials necessary for the
sustenance of the individuals to which they belong.
To this capillarity we also owe, in large part at least, the efficiency
with which the soil water attacks rocks, whether those which form the
massive substructure of the soil or bits which are mingled with the
detrital layer. By this attraction of fine interstices of the stone water
260 ORIGIN AND NATURE OP SOILS.
is sucked into its inner parts, taking with it the charge of GOs which
promotes the process of decay. In this manner the soil water operates
continually to break up solid parts of the earth and by the process of
rotting brings them into the dissolved state from which they may pass
into the realm of plant life. Thus the ground water not only acts as
the intermediary between the mineral and the vegetable kingdom, but
it is continually winning new materials to the state where they will
serve the needs of vital i)roce8ses.
It may well be noted that recent researches on the mode by which
plants take in mineral matters through their roots iwint to the conclu-
sion that the process of appropriation is assist^».d by the excretion from
the underground parts of the plant of some chemical substance, the
exact nature of which has not yet been determined. The true value of
this assistance which the plants give in the process of talking mineral
materials into solution has not yet been jiscertained in a definite manner.
It seems, however, safe to say that whatever l>e the result of further
inquiry in this direction we shall still, in the main, have to attribute
the fitness of the mineral material for the usi's of plants to the solvent
action of the carbonic dioxide contained in the water.
There is yet another physical property of water which has a great
influence on its action within the realm of the under earth. This is the
quality by which the materials dissolved in water are evenly distributed
through the fluid. It is easy to observe that when we place any i)ortiou
of a soluble substance in a vessel containing water the nmterial distrib-
utes itself uniformly through the mass; thus, if we droj) a little carmine
ink into a glass of the fluid, we note that without any stirring it ra])idly
mingles with the mass until every part is alike colored with the dye.
This diff^usive action o^ierate^ in the case of all substances which are
really dissolved, be they fluids or gases ; it acts, as we may note, through
the rapid diflftision of odors more quickly in the air than it does in fluids,
and more rapidly in water than in the case of other liquids.
The result of this process is that whenever ground water obtains in
one part of its mass a particular material, this substance in the state ol
solution is gradually diffused through the adjacent earth. The process
of diffusion goes on more slowly in the confined interspaces of the soil
than in a mass of unobstructed water, but it nevertheless proceeds in
an efftective manner. In this way a small portion of the ground water
which may be adjacent to mineral matter that affords the solution a
substance of a nature to be useful to plants does not retain this matter
in a small compass, but yields it to the neighboring fluid, and so greatly
extends the chance of its coming to the roots of plants. The effect of
this action is also in another way beneficial. Wlien in contact with a
particular mineral substance the ground water, but for this principle of
diffusion, would take up a relatively Large amount of certain chemical
materials and so become poisonous tx> the sensitive root. If there were
no influences of an equalizing kind at work the soil water would be
-1 EFFF.CT OF AIR ON SOIL. 261
locally Ao diverse in its mineral contents that the plants would not be
able to obtain uniform nutrition. By the operation of the diflftisive proc-
ess the roots have a much better chance of doing their peculiar duty
than would otherwise be afforded them.
The variations in the level of ground water have another important
influence on the soil, for the reason that they bring about a constant
movement of the air through the interstices of the earth. When, dur-
ing a heavy rain, the openings of the debris are filled with water, the
greater part of the air they contain wlien dry is expelled; as the fluid
drains away and the water level is lowered the atmosphere is urged
again into the spaces by the considerable pressure (about 14 pounds to
the square inch) which it ajiplies to the surface. Thus when the earth
becomes dry the soil generally contains air to the amount of from one-
tenth to one-twentieth of its mass. The next heavy rain which falls
repeats the process of expelling the air, and so in succession in moist
climates, many times each year, the wetting and drying of the earth
pumps the atmosphere in and out of the soil coating. In this way more
than the entire bulk of the earthy detritus is each season drawn into
and driven out of the soil.
The effects of this action are manifold. Some of them we may profit-
ably note. The air drawn into the soil serves to aid the roots in their
process of assimilating plant food. Most vegetables can not tolerate
conditions in which their roots are permanently bathed in water dur-
ing the growing season. This is the case with nearly all our forest
trees. A few species, like the bald cypress {Taxodium distichum
Rich.) and the tupelo (Kyssa uniflora), have managed to accommodate
themselves to a permanently wet earth by means of processes from their
roots which give sap in those parts of their bodies a chance to obtain
contact with air. These singular devices serve to show how important
it is for the soil to secure the repeated visitation of the atmosphere.
Another effect of the air on the soil is to promote the process of decay
in the mineral and organic matter of which it is composed. A certain
amount of this change will, it is true, take place beneath the water,
but in general these alterations are far less effective than when carried
on in the air. Thus while vegetable matter, after life is extinguished,
undergoes on the surface of the ordinary humid ground a complete
decay which returns all of its matter to the state of dust or gas, the
same material when buried under water only in part rots, the remainder
continuing for an undetermined time in the condition of i>eat, lignite,
or coal. The complete decay of this vegetable matter is necessary in
order that the ashy material may return to the soluble state from
which it can again be taken into the plants, and also in order that the
carbon may combine with oxygen and form COj, which, dissolved in
water, gives to that fluid the peculiar power of taking up mineral sub-
stances on which the utility of the soil for plants immediately depends.
Moreoveri were it not for this retoru of the carbou to the state of gas
262 ORIGIN AKD NATURE OF SOILS.
the atmosphere would soon be depriyed of the material and the leaves
would be unable to obtain the carbon with which they bnild the woody
matter. Whenever the entrance or exit of the rain is so hindered that
the earth does not nndergp those successive wettings and dryings which
characterize ordinary soils, the effect is to diminish the measure of fer-
tility which would otherwise characterize the deposit If the limit put
upon the successive uprisings and downsinkings of the ground water
be such as to keep the soil either excessively wet or dry, sterility will
characterize the district thus affected, though it might be otherwise
well suited for the nurture of plants.
There is possibly a third way in which the penetration of the air
brought about by the alternate wetting and drying of the soU is helpful
to vegetation; that is, the action of certain microscopic forms of vege-
tation akin to yeast plants. It is now deemed probable that some of
these lowly forms separate the nitrogen from the air and combine it
with potash or soda, thus forming the nitrates of those substances, of
which saltpeter is a familiar example. These materials are of great
value to plants as affording them nitrogen required in certain of their
functions. Although this element abounds in the atmosphere, vegeta-
tion can not directly appropriate it, but can do so only through means of
ammonia or combinations into which nitrogen has entered. Unless the
air freely enters into the soil and is frequently changed by an enforced
movement such as the variations in wetness, it seems doubtful if this
process of nitrification can go on. There are possibly other ways in
which these underground movements of the air affect the processes of
plant life, but these which have been g^ven are sufficient examples of
its action. They may serve, moreover, to show how the methods of
tillage, all of which rest upon the plan of stirring the soil, effect certain
of their beneficial results. Plowing, spading, and other modes of over-
turning the soil are, as unlimited experience shows, essential to the
growth of crops. Although these processes doubtless serve a diversity
of purposes, such as destroying wild vegetation and burying organic
matter which lies upon the surface, the most important effect probably
consists in opening the ground in such a manner that it is penetrable
by the air. The same influence is exerted in the successive tilling with
plows or other tools commonly given to ground occupied by crops whose
habit of growth makes such care possible.
Besides the extensive and varied work which water, in its free state,
accomplishes in the soil there is a large class of effects of other sorts
due to frost action, that is, to expansion by the freezing of the moist-
ure in the soil. In all the regions where cold is great enough to con-
geal the ground the effects of freezing are imi)ortant. At least half of
the land area of the earth is more or less exx)osed to this action in the
winter. The measure of the effect is, according to tlie intensity of the
cold, extremely various. We find that in certain cases the e^rth is sub-
mitted to a freezing which may, as in the border land of the tropics.
8HALKB.1 EFFECT OF FREEZING ON SOILS. 263
amount to no more than the occasional and brief congelation of the soil
to the depth of a few inches. Again it may in the frigid district about
the poles cause the earth to remain permanently locked in frost to tjie
depth of hundreds of feet below the surface, only the superficial soil
thawing during the summer season. As an instance of this permanent
and profound descent of the frost into the earth we may note the case
of the soil at the town of Irkutsk, near lake Baikal, in northern Asia,
where the freezing process has extended to the depth of over 700 feet.
Not only is the depth to which the frost penetrates exceedingly diverse,
but the nature of its action on soils of varied quality is likewise ex-
tremely diflferent. It will therefore be necessary in a somewhat careM
way to insi)ect the range of these actions which depend ui)on the con-
gelation of the ground water.
When the soil water is at any temperature above the freezing point
it is ceaselessly moving at rates of speed dependent mainly on the size
of the interspaces in which it is contained, the successions of rains and
droughts, and the steepness of the declivity on which it lies. Every-
where it is dissolving and distributing materials and yielding them to
the demand of the roots. As soon as it is seized with frost all of these
numerous ftinctions at once cease to be active, the water changes all its
qualities and becomes a mass as rigid as stone, x>erfectly inert, not only
itself dead, but locking all the life of the plants in a deathlike embrace.
Thus the frozen conditions mean to the soil the complete suspension of
all that vast range of mechanical, chemical, and vital operations which
constitute its physiology. A few of these actions we have already en-
deavored to trace, but the number of the operations which depend on
the fluid condition of water, and which cease when it becomes solid, is
vastly greater than it is possible to indicate in this sketch.
Although the effect of the soil water while frozen is to reduce the
whole of the detritus to the depth to which it penetrates to an altogether
inert state, the process of freezing and thawing when often repeated
has a noteworthy influence on the conditions of the ground. The ways
in which these eftects *are brought about are somewhat complicated.
The process of solidification in the case of water, as in that of many
other substances, is attended by the formation of crystals. Save in
snowflakes these crystalline forms are not ordinarily visible in ice, but
often they may be detected by pouring a thin, colored fluid upon the
surface of a block of ice when it is near the melting x>oint. The liquid
will then be seen to penetrate along the planes of the crystals, thus in-
dicating their presence, which, because of the transparency of the mass,
might not otherwise be evident. The old ice of our northern rivers may
in the springtime often be seen in a shattered form where it has been
swept against a bank at the time when the streams break up. In such
masses we may often observe the massive separate fragments, each
constituting a dagger-like bit some inches in length.
Instructive examples of another effect of frost on the ground water
264 ORIGIN AND NATURE OF SOILS.
may be seen where a sharp frost iu spring or autumn comes upon wet
clayey ground. The ice is often at that time developed as a thick-set
mass of slender columns, which constitute a bristling coating in aud on
the upper part of the soil. Each of the slender bits may have a length
of several inches and a diameter of a quarter of an inch or more. It
often happens that we find a layer of earth and small stones which
originally lay on the surface of the soil uplifted by these crowded col-
umns to a height of several inchcH above their original level. With a
little care the process of growth can be tolerably well observed; we
perceive that separate pieces of ice begin to form between the bits of de-
bris which cover the ground; they grow by additions to their bases due
to the successive freezing of the water which the soaked earth affords as
they form ; they shear the earthy matter apart and rise i)erhaps to the
height of half a foot before the morning sun arrests the process of aug-
mentation. Owing to the oi)en spaces between the slender shafts the
ice does not hinder the cooling of the water from which they are formed
as it would if the frozen mass wei*e united in the form of a sheet.
It is a noticeable fact that the i)eculiar si)ecies of ice forms above
described is commonly produced only in the autumn, when the ground
is warm and the air cold; it occasionally though more rarely occurs in
the spring, when a cold period follows one of sufficient warmth to bring
up the temperature to the thawing point. The reason for this probably
is that unless the soil water is moderately warm the frost x)enetrates the
ground with such rapidity as to form a continuous ice sheet, thus arresting
the growth of the uprising columns. It is interesting to note the sharp
contrast between the condition of growth of this columnar soil ice and
what is known as hoar frost. Hoar frost branches grow by accretions
to their upper extremities ft*om water congealed from the atmosphere;
soil-column ice by additions to the lower end derived from the earth
water. It is also interesting to note that this last form of ice exercises
a considerable overturning effect on the superficial XK)rtions of the soil;
although the action is most visible on tilled ground, it often occurs
below the leaf-clad surfaces of woodlands.
The formation of ice similar to that above described but occurring in
a less perfect way takes place in the interspaces of the soil as far down
as frost penetrates. By this action particles of soil are slowly but vio-
lently thrust apart and ground against each other so that. they are
affected somewhat like grain in a mill. This process extends the com-
mingling of mineral and organic matter and serves to make the soil
material more soluble. The effect of these frost movements on the soil
are not readily discernible for the reason that they go on in an invisible
realm, but we can easily note a number of facts which show us some-
thing of their nature and effects. All persons who dwell in regions
where the earth freezes deeply have noticed the "heaving" effect of
frost upon various objects which are planted in the soil. Fence posts
if their bases are not placed so deep as to be some distance below the
SHAUSB.] EXPANSION INDUCED BY FREEZING. 265
zone of freezing will gradually be uplifted by the successive movements
of the soil until they fall over upon the ground. They are dragged up-
ward by adhering earth each time freezing occurs and the soil is forced
to expand; when the melting time comes the thawing process, begin-
ning at the base of the frozen section as well as at the top of the ground,
releases a certain amount of debris from the frozen state and allows it
to slip under the base of the post, so that when the ice is entirely melted
away the timber can not return to its original position. The same action
takes place in the case of stones which by natural processes may have
come into the soil. The tendency of freezing is to lift them above their
beds and linally to leave them on the surface of the ground. As we
shall see hereafter this action of the frost is directly the reverse of that
brought about by the work of plant roots and burrowing animals, which
tend to remove the soil from beneath stones and to aecumulate material
on the surface in such fashion as to bury the masses. Where plants
possess long and tapering tap-roots, such as those of red clover and
many cultivated vegetables, the effect of this heaving action is often
such as to throw the plant quite out of the ground. This rarely occurs
to the wild species for the reason that they have adapted the shape of
their roots to meet the dangers which the heaving of the soil imposes.
The expansive movement of the soil under the action of frost is in
good part due to the fact that water, unlike almost all other substances,
has the eminent peculiarity of expanding on becoming solid, the increase
in bulk amounting to about one-tenth of the mass. On level soil the
thrust which this expansion brings about causes an upward movement
in the frozen mass; if the soil is frozen to the depth of 2 feet the rise of
the surface may amount to half an inch or more. When the ice melts
the particles of earth fall back into the place whence they had been
driven. When, however, the surtace has a distinct slope, as is the carse
with the greater part of land areas, the influence of gravity may lead
to a slight movement of the expanded coating of detritus at the time ot
melting in the direction in which the surface inclines. When the frost
passes away the fragments of which the soil is composed have been
pushed apart by the ice crystals so that they are not in perfect contact
with each other.
The reader has doubtless observed the peculiar softness of the ground
after the frost leaves it. This open nature of the detritus is due to the
fact that bits of earth after freezing do not cling to each other as they
did before they were separated by the freezing action. Now, when on a
slope even of moderate steepness, a soil thus made incoherent again set-
tles into a firm mass, there results a slight movement of the debris down
the slope, which, repeated often during the winter and year after year,
causes the soil in frosted countries where the declivities are tolerably
steep gradually to move downward toward the stream. From obser-
vations made in northern Kentucky I have determined that on a slope
of 6 degrees inclination a deep clay-loam soil moved downward at Uie
266 ORIGIN AND NATURE OF SOILS.
rate of about 1 foot in fironr 10 to 20 years. In some cases the creeping
movement is probably yet more rapid, but in general it is doubtless,
save on slopes of great declivity, considerably slower.
An important effect arising from this downward movement of soil is
due to frost action. The amount of freezing is greatest in the upper
part of the soil and diminishes as we descend. The result is that par-
ticles of detrital matter are shoved over each other in such a manner as
to disrupt them. Something of the same action is brought about by
the growth of roots. These processes of plants are largest and most
numerous in the upper part of the soil. By their action the debris is
pushed apart; when they die and decay, openings are left into which
the soil again falls. Naturally this movement is most considerable in
the direction of the declivity. At the foot of soil-covered hillsides we
often find a brook the banks of which are formed of soil presenting newly
cut faces. The freshness of these little escarpments makes it evident
that the debris must be constantly pushing against the stream; were
this not so, the steep faces would si)eedily break down and become
covered with vegetation. Wherever frost operates it is a most effective
agent in supplying to the streams the detritus which they convey to
the alluvial plains and to the sea. To this action we may in part, at
least, attribute the fact that in high latitudes the d<5bris arising from
the decay of the under rocks generally forms a thinner coating than
in the regions nearer the equator.
Although the effect of frost in hastening the movement of detritus
down the slope toward the streams doubtless in part accounts for the
relative thinness of the soils in high latitudes, something of this feature
must be attributed to the comparative slowness with which rocks decay
in cold climates. In such regions the effect of vegetation on the min-
eral materials is limited to a relatively brief season, and for a consider-
ably part of the year all rock decay is arrested by the frozen condition
of the earth.
Not only does the action of freezing water profoundly affect the con-
ditions of the soil in the ways above mentioned, it is also of consequence
m the economy of the earth in several more remote ways of action, only
one of which is of sufficient importance to demand our attention. This
particular influence is brought about by the disnipting effect which
freezing water exercises on the rocks into which it penetrates. An
excellent example of this action may be seen in any slate quarry where
the workmen set the seemingly solid blocks of stone in a position where
the edges of the cleavage planes face the sky; water entering into the
invisible crevices between the sheets of slate and there expanding, in
the process of freezing, will usually in a single winter open the cleavage
planes so that the flakes may be readily separated. On any cliff, or
even on the rocky siunmits of mountains, the effect of this frost action
may be seen in the great number of blocks of stone which the winter's
frost has riven from the firm-set mass. In the upiwr ijortion of Mount
s
i
'ii
n
u
^
^
8HALEB.] EFFECT OP DISRUPTION OF ROCKS. 267
Washington, !N"ew Hampshire, where the rocks are scantily soil-covered
and are thus exposed to freezing, the surface is so thickly strewn with
these frost-detached masses that it is hardly possible on certain fields to
obtain a sight of the unshaken bed rock.
The work of frost on masses of stone is by no means limited to that
first stage of their disintegration which consists in riving them from
their matrix. As fiaist as decay of any kind ox>eii8 the structures of the
masses the water penetrates into the pieces and in freezing them serves
to break them into small bits. This process is not arrested until the
fragments become so small that they are less in size than the finest
grains of sand. Even where the rock has no distinct joints or cleavage
planes into which the water can penetrate the fluid is likely to soak into
the substance of the stone, and if its elements be not very firmly bound
together the freezing will scale a layer of the material from the outer
part and tliis thin sheet will readily fall to powder in subsequent proc-
esses of decay. This scaling process takes place most commonly in the
case of rocks which have a rather open texture, such as is found in some
forms of granite and in most sandstones; it is so powerful an agent of
decay that many stones which in the tropics endure very well crumble
to pieces in high latitudes. An instance of this frost effect is afforded
by the so-called Cleopatra's needle, an obelisk which of recent years has
been brought from the frt)stless land of Egjrpt to the climate of New
York. Exposed to the open air in its new position the process of decay
is going on so rapidly that before the end of the century the stone will
probably be more effectively disintegrated than it had been in 2,000
years in its original location.
In several ways the disruption of rocks greatly aids the action of
chemical agents of decay, which serve to bring rocky matter into the
soluble state in which plants may make use of it. In general chemical
forces act only upon the outside of rocky matter. As the particles of
rock grow smaller the proportion of superficial area to the mass is
increased, and this in a rapid ratio. Thus a cube a yard in size exposes
64 square square feet of surface; if divided into cubes of 1 foot each,
the aggregate surface exx)osed to corrosive action is increased to 162
square feet. If it is broken into cubes of 1-inch mass, the material then
presents a total surface of nearly 2,000 square feet ; still further reduced
to bits of one-twelfth of an inch in diameter, the exposed faces of the
rock are increased until their surface is equivalent to about 20,000 square
feet, or nearly half an acre in area. In the finer bits of earth, such as
compose the principal part of the mineral matter contained in the more
fertile soils, the total area of a cubic yard of rock which in the original
massive form exposed an area of only 54 square feet to the chemical
action which prepares such substances for solution in soil water, and
thus for the use of plants, may be increased until it amounts to some-
thing like ten thousand times the original area. So far as frost action
aids in comminutiug the rock it is a beneficent agent of very great
268 ORIGIN AND NATURE OF SOILS.
importance. The effeet of freezing is naturally most conspicuouH in the
regions where the ancient soils have been removed by glacial action.
In all the fields where the ice of the last glacual epoch has done its sin-
gular work of abrasion and has stripped away the ancient soils the
expansive action of freezing water does much to help the restoration of
the e^rth to the state wliere the higher x)lants can be fed. In the trop-
ical and other districts beyond the motion of the frost the process of soil-
making la(*>ks this aid, but tliere the generally increased rainfall and
the absence of long-ciontinued frozen condition of the earth which com-
monly attends frost action serves in part as a com})ensation for the
absence of this rock-disnipting fore^*. (see PI. x).
Before leaving this interesting x>ortion of our inquiry, we should note
the fact that the heaving or interstitial movement of the soil produced
by freezing has an imiKirtant influence on the ease with which water
enters its mass. The action of gravity in the soil itself, combined with
the weight of the winter's snows and that of the forest trees which gen-
erally cover fertile soils, tends to give to the earth a measure of comi>act-
ness which is undesirable. By these actions the soil is often made so
dense that the watt^r does not easily penetrate it; when the frost leaves
the ground, we find, as before noted, that the earthy matter is so open
that it may contain a large amount of water which has found a place in
the crevices formed by the heaving of the mass due to the expanding
ice crystals. In this manner, in regions where the frost penetrates to a
considerable depth, the soil is secured against the evils of excessive
solidification* When the frost departs the ground is left in a state
analogous to that which is given to it by the work of the spade or plow ;
the slender and weak rootlets which plants in the growing season put
forth find their passage through the earth made easy, and the food-bear-
ing water can easily range through the open-textured mass.
EFFECT OF ANIMALS AND PLANTS ON SOILS.
This division of our task concerns that part of the preparation and
maintenance of soils which is effected by the x)lants and animals that
by their habits are intimately related to the detrital coating of the earth.
This group of results due to the action of organic life is to be classed as
hardly second in importance to those brought about by the action of
water. The influence of organic life on the soil is effected in a variety
of ways, only the most important of which can be here considered. For
convenience, these effects may be classed in the following groups:
First. The influence of organic species on the rocks from which the
soil derives its mineral constituents.
Second. The modification of the soil through peculiarities in the life
habits of animals and plants which occupy it.
Third. The contribution made to the soil by remains of the organic
forms which have occupied it.
(1) ThQ first of the above-named classes of action may for the present
PHALKB.] ACTION OP PLANT ROOTS. 269
be briefly dealt with for the reason that it will have to be again con-
sidered in some detail in the section of this paper concerning the rela-
tions of the soils to the underlying rocks whence in good part they are
derived. Briefly, the facts are as follows, viz : The greater i)art of our
rocks owe the measure of their fitness for producing good soils to the
store of nutritive materials placed in them when they were formed on
the sea floor by the creatures which inhabitc»d its waters when they
were constructed. The sediment of which these rocks are composed
contain, in varying proportions, lime, phosphorus, potash, soda, and a
host of combinations of these and other substances which to a great
extent owe their deiiosition in the strata to the work of organic species
which aided in accumulating the sediments.
(2) The immediat(»> influence of living beings on the soil is exhibited
in manifold ways; of these we shall first examine those due to the
plants. When, as in the case of the lower forms of vegetable life, such
as lichens, the individuals have no true roots, the effect of their growth
upon the soil is x>urely secondary, i. e., it is due to the contribution they
make by their death to the earth in Avhich they grew and to the reaction
brought about by the COj which they contribute to the soil water.
When, as is the case with the greater part of the plants which grow
upon ordinary soils, roots exist which search downward into the detrital
layer for their appropriate food, vegetation exenjises a great mechanical
effect upon the soil coating. Each root is, at the time of its beginning,
a slender thread-like object, which extends itself through the inter-
stices, between the bits of debris which compose the earth in which it
grows. At first it has a very slight power of displacing the soil ; when,
however, it effects a hxlgment in the crevices of the under earth and
finds sufficient food to warrant its further growth, it rapidly increases
in size and vigor of development. From a slender fll)er, having a diam-
eter of perhaps one three-hundredth of an inch, it may increase to be
a foot or more in diameter, as in the case of our larger forest trees. In
the process of growth the root, after it has gained a considerable tliick-
ness, energetically i)ushes outward; when it is even as much as half an
inch in diameter it may exercise a powerful wedging action. By the
larger roots of our forest trees the soil is often, in the course of a genera-
tion of growth, in a surx)rising manner moved to and fro. The effect
of this movement is to grind the particles of soil against ejush other and
thus to advance the work of diminishing their size and of making them
more ready to pass into the state of solution (see Fig. 7).
When a growing root penetrates into a crevice in the rocks and ex-
pands in its further growth, the effect of its action in disrupting the
mass may be very great. We may often find fragments of any kind of
stone which affords plant food, especially those varieties of limestones
of the richer sort, qnite. interlaced and- shot through by the fibers.
Where one of them finds a fissure and enters the mass it is almost cer-
tain to disrupt it in the course of growth. As fast as decay softens the
270 ORIGIN AND NATURE OF SOILS.
stone and opens little spaces in tbe plaueH between ttic graiiiH of which
it is composed or along its joitit i>lanes, the flmall rool^ i)enetrate these
fissures and break up the defrayed portion of the mass, in this manuer
opeuing the inner portion to the access of chemical agents which pro-
mote decay. When the roots find their way down to the level of the
bed rocks which underlie the soil, provided these strata are much divided
by joints or bedding planes, divisiona of extremely common occurrence
in most rocks, the Ti)ot» olten find access to these incipient fractures in
which the penetrating waters have already produced a certain amount
of corrosion. Expanding in the crevice the roots which come first break
Fio. 7.— Effeot of nnti of tree* uu the formatloD of auU.
Up the rock and open its structure so that the next wliich penetrate
may have freer access and extend tbe demolitioTi. This deep root work
is mainly performed by certain forest tnses, such as our walnut's, which
have the habit of sending down a strong tiip root whi<;b often penetrates
10 feet or more below the surface of the earth. These tap-root trees
have a certain advantage in the struggle for existence, arising from the
feet that they feed in depths wherennto the roots of other species do
not attain, and they thus secure a field where they do not have to con-
tend for food with a boat of competitors. Where these tap-root trees
grow in abundance tbe soil is generally deep, partly for the reason that
such species flourish best on soils of this deacnption, but in tbe main
because they are by their habits the most potent agents which tend to
disrupt the solid under rocks and give their fragments to the uses of
BBALBR.) EFFECT OF DECAYING ROOTS. 271
the soil. As loug as the bed rocks lie iu a firm-set mass the agents
which serve to rot them have little chauce to do their appropriate work,
for, as we have seen, the incidence of decay increases in a rapid ratio
with the division of the stony matter. Serving as the roots do, inci-
dentally, to break up the underlying rocks, they are agents operating
to deepen and enrich the undersoil. They act substantially like subsoil
plows.
When a district is occupied altogether by forest trees or other plants
having roots which x>enetrate to no great depth the tendency is to divide
the soil into two distinct layers, the true or upper soil and the false or
under soiL The upper layer or the zone occupied by the roots exhibits
that combination of decayed mineral and organic matter which we have
found to be the essential elements in the construction of soil. In the
lower-lying layer we have the mineral matter alone, which, while it ex-
hibits the effects of the chemical action of the ground water, is much less
easily penetrated by decay than that which is found in the true soiL
The origin of this under soil is plain: its formation is due to the action
of the agents of decay below the level to which the roots have pene-
trated; in certain common classes of rock, particularly in limestones,
the chemical decay often advances downward at a much more rapid
rate than the roots penetrate into the earth. We may thus have, as is
the case in many parts of the country lying south of the glaciated region,
very deep false or under soils, while the truly fertile layer, owing to the
fact that the roots have not penetrated deeply into it, remains compact
and unsuited to the uses of plants until it is artificially mingled with
the vegetable waste as by subsoil plowing.
If the reader will examine any cubic foot of ordinary forest soil he
will find that every part of it is occupied by the roots of trees ; generally
there is not a cubic inch of the mass but contains one or more of the
fibers or terminal twigs of the underground branches of the tree, and
often there is a branchlet of the roots in every cubic line of the mass.
Many of these roots are in a way experimental ; they are sent out by
the plant in a reconnoitering manner to see if a particular part of the
ground affords nutriment; if the search is successful they enlarge; if
they fail to derive suflicient support then they die, and their organic waste
is by decay added to the deposit. It is easy to observe that the open-
air branches of the tree are continually dying and returning to the earth,
though the plant itself may be in a flourishing condition. A similar
pruning occurs in the underground branches of the roots. As these lop
off, a portion of their substance decays and is absorbed by the water and
yielded to other roots. It is indeed to a considerable extent to the decay
of roots that the deeper part of the soil is supplied with the carbonaceous
matter taken by leaves from the atmosphere in sufi&cient quantities to
maintain the nutritive quality of the detritus. The decaying roots, when
they are of considerable dimensions, serve also another curious function :
as they rot away they leave open channels through the soil which some-
272 ORIGIN AND NATURE OF SOILS.
timeA extend for a diHtance of 30 feet or more, and occasionally, when
they belong to the tap-root species, in a yertical direction for 10 or 15
feet. The compaction of the soil which is eflfected by the outward push-
ing of the root in its process of growth, especially where the earth has
not been influenced by freezing, often causes these old root channels to
remain open for a long time after the woody matter has dissolved away.
Thn)ngh these tubes the water finds a path down to the under soil, and
by these means the excess of the fluid is to a certain extent removed as
if by a drain pipe. In an old forest these water ways often serve the
purpose of drainage in a singularly perfect manner, the water finding
its way deviously but effectively from the path of one dead root to
another until it escajies into an open stream.
While the roots are constantly contributing to the vegetaljje matt-er
in the soil through their partial decay, the upper branches of the tree
are sending down even a larger share of vegetable matter to decay in
the bed of the forest mold, and at the death of the plant the whole of
its substance returns to the earth. The amount of woody matter which
a single forest tree of moderate size during its lifetime contributes to the
earth is surprisingly great; it commonly amounts to many times the
weight of the living tree at the date of its full maturity. This con-
tribution of vegetable matter arises from the annual fall of leaves and
the occasional and generally frequent dropping off of branches, and also
from the exfoliated bark, which is considerable in quantity. It is safe
to estimate that in the more luxuriant primitive forests, such as flour-
ished in the Appalachian district of this country, the amount of this
vegetable matter which falls to the ground each year is sufficient to make
a layer of compact forest mold at least an inch thick over the area
occupied by the wood. Although this process of accumulation has been
going on for milliouH of years in the region south of the glacial belt, the
sheet of decayed vegetable matter usually does not exceed a foot in
depth, and even in rather moist woods, where the material is best pre-
served, it is rarely found more than 2 feet thick. This fact shows us
that there is some process at work by which the layer of vegetable mat-
ter continually passes away from the surface of the earth.
The removal of the forest mold is accomx)lished by a simple chemical
process. Woody matter is composed in large part of carbon, which the
plants have taken from the atmosphere, where it exists in the form of
CO2. To obtain this carbon the plant breaks the gas into its elements,
allowing the oxygen to go back into the air, while the carbon is built
into the tissues of the plant. The lesser part of the woody matter con-
sists of various substances, such as lime^ potash, soda, iron, silex, etc.,
which the plant has won by its roots from the soil. The process of decay
operates through a simple reversal of the chemical changes which took
place in the formation of the wood. The carbon recombines with oxygen,
forming once again CO2, and the mineral substances dissolved in the
rain water return to the soil and are ready to renew their work if taken
NBALBB-I EFFECT OF OVEETUKNED TREES. 273
np by the roots of plants. If we examine a sef^tiuu throu^b tUe forest
mold we may see every stage of this beautiful reversionary process.
On the sur&ce lie the newly fallen leaves and branches scarcely affected
by decay; an inch or two lower down we find the debris which was
accumulated a year ago partly rott«d and breaking to pieces fh>m decay ;
a little forther down we can no longer trace the original shape of the
vegetable matter, and at the base of the nection we observe that there
is a mass of confused earthy and vegetable matter which shades down-
ward into the true soil, where the roots do their work. It probably
requires on the average nut more than a score of years fur the leaves
and twigs entirely to pass back either into the soil or the air, so that
the available matter which they contain is not loug kept from the uses
of life.
— Fint effect of aTertarneil Ii
mnlMed in pit. (See ■!» Fig. 3.)
The intermixture of the leaf mold and the mineral inatter is in part
accomplished by the action of roots in the manner before described and
in part by the operation of various agents which serve to bring consid-
erable amounts of the surface accumulation into the soil. This process
of inhuming organic matter is in » measure brought about through
certain accidents which occur to the trees and in part by the action of
various kinds of animals. When a forest tree dies by old age or dis-
ease it« greater roots decay, leaving large o|)enings extending from the
surface to a cousiderable depth. While the.-4e cavities remain open the
rains and winds bear fallen leaves and small twigs into them, and thus
a certain amount of vegetable matter formed in the air enters deeply
into the under earth. When a forest is overturned by a strong wind
the trees, unless they be tap-root species, are commonly torn from the
ground or uprooted, and thus it occurs that the soil about the base of
the bole is rended away so that it lies at right angles to its original posi-
tion. This mass of uprent roobs is often as much as 10 feet in diameter,
12 GEOL 18
274 OBIGIN AND NATURE OF SOILS.
and containa a cubic, yard or more of Boil. The pit from whicli it has
been torn is often a or 3 feet in deptfa. This eavity quieklj- becomes
filled with vegetable waste., and as the roots decay the earth wliich they
interlock gradoally falls back upon the surfai^e whence it eame, burying,
it may be, a thick layer of leaf mold to the depth of a foot or two below
the 8nrta*:e. (See Figs. 8 and 9.) In certain part« of the country
wliereluirricanes are of frequent occurrence the amount of vegetable
waste thns buried is consitlerable.
Fio, ).— FilUl efltet of ovcrtnnuxl Iroe* nn soil. a. leaf niolil; b. eoll Tmllvn rrom rouU; c, iWnjed
wiMd nmn raoU,
By far the greater part of the work of mingling the waste from the
aerial parts of the plant with the soil, at least on the upland distrittts
of the earth, is accomplished by the action of animal life, particularly
by that arising from the numerous 8i>cciea which burrow in the earth.
So wide is the range of these a«-tions that it would require a lengthy
treatise to consider them in a detailed way. Wo can only note the in-
fluence which certain forms exert, and it will be convenient at the same
time to consider si>me other effects lu-complished by thej*e burrowing
species as well as their influence in intixiducing the vegetable matter
into the under earth. We shall begin this study with the earthworms,
A group which Charles Darwin has admirably shown is exceedingly ef-
fective in determining the conditions of the soil.
In common with many of their kindred which dwell on the sea floors
these vermiform animals which inhabit the soil are accustomed to ex-
cavate bnrniws extending from the surfiu'C of the earth downward to
a depth of 2 or 3 feet below the light of day. In their up-and-down
journej-ing the creatures in part thnist the earth aside, but in larger
measure they create the oiH'uing for the progres.s of their bodies by
passing the soil througli their alimentary canal. Taking the earth into
their stomachs the process of dige^tiou removes from it such nutriment
■HiLM.] ACTION OF EARTH WORMS. 275
AK it may contain, while tlie remaiuder, nearly as great in bulk an that
which was eaten, ia thrown out as excrement. Every one is familiar
with the casts or dung which these worms are in the habit of deposit-
ing on the surface of the ground near the mouth of their burrows when
they for a little time escape from the earth. Each of these little heaps
contains a portion of a cubic inch of soil which has been brought up
fi^in a depth of from 6 int^hes to 3 feet. As in single fields there are a
hundred thousand or more individuals of these spet^ies to the acre, the
amount of earth brought up to the level of the air is in each year con-
8iderab1<\ In the regions where these animals abound they probably
bring an annual contribution as much as oue-tenth of an inch of earth
from the underground Ut the top of the soil. There is thus laid aima tiie
decaying vegetation or mingled with it in such a manner as to constantly
bring the organic matter into the buried condition enough material
ftom the depths of the earth to produce a slow overturning of the whole
soil layer.
Although the effect of this action of the earthworms in any one season
is slight, yet when continued for centuries the result is to bury all the
objects of a small size which lie upon the surface to a considerable
• depth; ancient implements, such as stone arrowheads which the early
peoples have drojiped ujmn the earth, are soon coverwl over wherever
the earthworms abound. Old tombstones are gnidually buriwi with the
dust which they commemorate and even the smaller churches of En-
gland the floors of which were orginally a little above the surrounding
ground, become in time so heaped about by the earth which the worms
have drawn from underneath their foundations that their floors lie
below the level of the soil (See Fig. 10).
The ejirtbwonns, as Mr. Darwin han ;idmirably shown, have a singu-
lar habit of drawing down into their burrows the dead leaves which lie
on the surfat^e of the earth. In performing tliis work, though they are
destitut* of sight organs and imijerfectly prf»vided with any other kind
of sensory apparatus, they exhibit a certain amount of discretion. They
rarely seize on leaves which from their size or shaiie can not be dragged
into the slender tubes which they inhabit, but they select for their use
276 ORIGIN AND NATURE OF SOILS.
blades of grass and narrow-leaved fomis, such as netnlles of the pines.
The latter they generally lay hold of at the base where several leaves
are joined together rather than at the extreme divergent point of the
bunch, and in this they exhibit a certain amount of intelligence, for if
they did not exercise this choice the fasicule of the blade would catch
at the mouth of the burrow in such a manner that it could iu)t be drawn
downward. It is not certain what the end is which these creatures
attain by this curious habit, but it undoubtedly serves to introduce a
good deal of vegetable matter into the under earth.
The effect of earthworms upon the superficial detritus would be greater
but for the fa<;t that they rarely inhabit the forested parts of the
country, and moreover they do not live in soils which are of a very
sandy nature. The thick coating of decaying leaves in the woods evi-
dently makes it difficult to escjape to the surface in the manner which
is required by their mode of life and the sandy soils contain too
little nutritive matter to serve their peculiar needs. Where they do
their work they are in many ways useful to the soil ; besides introducing
vegetable matter below the surface they greatly aflfect the earth by
continually passing the mass through their bodies. In their stomachs
they have certain hard parts which probably serve in the maimer of a
mill to pulverize the material. Moreover, the se<Tetions which aid in
the process of digestion operate to bring the mineral matter which they
swallow into a state in whi(^h it is more readily dissolved in the ground
water and thus put into the service of plants. As in the course of a
century all the soil except its coarser parts is, in a field plentifully oc-
cupied by these worms, submitted to this organic process the aggregate
effect on its fertility is gre-at. Tlie burrows which the creatures form in
the earth also aftbrd passages by means of which the water enters freely
into the depths of the soil, and as this water settles down it draws in
the air and so aids in that process of aeration which is favorable to the
growth of plants.
The higher insects have very great influence) in the develoi)ment of
soils, though on the whole it is less definite than that of earthworms.
A large ])art of the multitude of si>ecies of this group of animals, par-
ticularly the beetles, for a considerable period of their life inhabit the
under-earth. This subterranean condition continues while they are in
the grub state, which in certain forms, as for instance in the 17-year
locust, often endures for a year or more. During their tenancy of the
ground they much affect its conditions by their movements and secre-
tions. Many speides of beetles while in the gnib stiite burrow in the
earth somewhat in the manner of earthwonns. They devour vegetable
mattt^r and deliver the residue in their excrement to the soil ; they often
die under ground, and their bodies are added to the store of nutriment
available for plants.
Certain groups of beetles have peculiar habits of conveying sub-
stiinces from the surface into their burrows where they are lodgetl at
some depth beneath the earth. Thus the carrion species lay their eggs
8HAUKB,] ACTION OF ANTS. 277
in the dead bodies of the smaller mammals and birds, whereby they
provide for their young an opportunity for obtaining abundant food.
After placing the eggs in the carrion they proceed to bury it so that it
may not be consumed by other animals; the inhumation also serves to
prevent the too rapid deejay of the flesh. As this action goes on in forests
and fields alike and in almost all countries, the soil receives a consider-
able amount of fertilizing materials which would otherwise be denied it.
Several species of beetles seek for the dung of the herbivorous mam-
mals; this material they shape into balls, in which they lay their eggs.
The rounded masses are often half an inch or more in diameter, and
after these are shaped they are carefully and laboriously conveyed to
vertical shafts which the parent insects have excavated in the earth to
the depth of from 6 inches to a foot below the surface. In each of these
little balls an egg is laid, the product of which is sheltered and nour-
ished by the dung, so that the young creature is provided with a means
of subsistence. A single i)air of these beetles will in one season intro-
duce into the earth several cubic inches of fertilizing material.
Although the solitary insects do a large amount of work within the
soil, the principal influence exercised by this class of animals is brought
about by the colonial forms, such a« the ants, the ground bees and
wasps, and the termites — white ants, as they are sometimes called. The
greater part of the spe(ues belonging to these orders build their habita-
tions and live the major portions of their lives in the detrital zone of
the earth. They belong in nearly all lands, and are often so abundant
and so active in their work that they much affect the character of soil
in districts which they inhabit.
Of the forms above mentioned the ground bees are the least important.
They excavate small burrows and fill their spaces with their winter
stores, and a considerable part of their bodily and household waste is
healthfiil to the plants. The shafts and galleries of their abodes, though
generally protected with some skill against the entrance of water, help
to x)rovide the ways by which that fluid may enter and leave the earth.
It is, however, characteristic of the bees that their colonies are never
planted close together, and thus the aggregate effect of their under-
ground life ui>on the soil is inconspicuous. It is otherwise with their
kindred, the ants and termites, groups which often exist in amazing
plent}^ and are found in most countries beyond the arctic circles, where
the soil affords conditions which allow them to carry on their peculiar
life; therefore, to this group we shall have to give somewhat special
attention.
One species of social ant, the Myrmica barbata of Texas, commonly
known as the " agricultural ant," appears, acijording to trustworthy au-
thorities, to have the remarkable habit of clearing away the natural vege-
tation, or at least the slight annual undergrowth, from a bit of ground
near its habitation. On this surface it plants particular species which
afford nutritious grains. If the conclusions of the observers are correct^
278 ORIGIN AND NATURE OF SOILS.
this creature is tlie solitary animal besides man which has invented any
kind of agriculture. Singular as this habit appears to be, it is hardly
more surprising tlian certiiin other customs of these curious insects.
Where we find organized slavery and a well ordered system of keeping
other insects, such as the aphides, which secrete nutritious juices, in
well arranged dwelling ])laces about the stems of plants on which they
feed, it is hardly surprising to hear that the ants have come to a state
of development in which they sow and reap. This peculiar relation
of the agricultural ants to the soil is, however, limited to a small area,
and is therefore without much effect on the conditions of the earth.
In general it may be said that the several species of ants dwell only
where the soil is of tolerable depth and fertility and where it is at the
same time of a somewhat sandy nature. They avoid the tough clay
because it holds so much water as to menace the drowning of the colony.
Where the soil is extremely siliceous and therefore barren, they avoid it,
for in such very arenaceous districts there is a lack of sufficient food. In
regions where the winter's cold is great these creatures construct their
permanent habitations so that they may be lodged in chambers at a good
depth below the surface, and thus be protected from the frost. In
tropical countries some species of true ants, as well as the so-called
white ants or termites — which are not indeed ants at all, but belong to
the order Neuroptera — ^build their habitations altogether on the surface
of the ground. Other sx)ecies, such as the ordinary black ants of North
America, have their dwelUngs partly above and partly below the sur-
face. However varied the architectural habits of these creatures may
be, and the variety in this regard is exceedingly great, they are all
fashioned so as to take large amounts of ea^rthy matter from the depths
of the soil and heap it upon the surface. Thus our ordinary brown ants,
which have their dwelling places entirely below the surface of the earth,
may be seen after every season of rain, and to a certain extent after
periods of drought, busily engaged in dragging up grains of sand from
the subterranean chambers of their dwellings. This mineral matter
they store about the mouth of the vertical shaft which gives access to
the abode. On a field in Cambridge, Massachusetts, observations made
during two summer seasons showed me that the average transfer of soil
matter from the depths of the surface of the earth was in the aggregate
sufficient to/orm a layer each year having a thickness of at least one-
fifth of an inch over the area on which the observation was made,
which is about 4 acres in extent.
The common species of American crawfish have, in certain parts of
the country, developed a peculiar habit of boring long underground
tunnels in soils which are at once of a moist and clayey nature. These
openings are generally about an inch in diameter and consist of hori-
zontal galleries occasionally extending for a distance of scores of feet
and terminating at the end either in the margin of a neighboring stream
or in a shaft which extends upward to the surface. These tunnels some-
"HALM] EFFECT OP CRAYFISHES. 279
times serve in a rpiuarkably effective way Ui drain off the excess of soil
wat«r and permit the entrance of air into the earth — a jiroceHS which,
OH we have heretofore seen, is of importance in tlie interests of plants.
It seems to be commonlybelievediutlieeoimtries where these creatures
abound that tliey are in »ome way the cause of the marshy eliaiw^ter of
the ftehls which they inhabit; the land they oc^npy is termed c^rawflshy
and the blame for its over wet condition is laid iii>on the animals, although
tlie eSei-.t of their action is often so far to remove the excessive water
that the area is forest-<Uad instead of bein^ a characteristic marsh.
Along the banks of the Mississippi and its tributaries, particularly
those which drain into its i)riiici|>al affluent, the Ohio, crawfishes once
abounded in greitt number and did good service in promoting the escape
of the ground water from the clayey alhivial soil. Of late the pigs,
which in this ]iart of the country are allowe<l free range of the forests,
liave ai^uired the habit of feeding ou these crawfish, particularly at
the season of the year when they haunt the stream-beds. At sach
times pigs may be seen busily occupied in turning over the stones and
drift winkI l)eneath which their prey seek a refuge &om their uatunvl
enemy, the water birds, but which afford no protection to these modem
pursuers. The infliience of this destru<!tion of these natural drain-
makers appears to be already visible in the increased wetness of many
tracts of low-lying alluvial sail where trees once flourished, but where
they are now dying out fn»ni excess of water.
Fio. n—Edfec-t nf aiit-hiUii on hiU. sd
The effect of this transfer of material IVom the lower levels of the
soil to its surface is jierhaps even greater in the case of the larger species
of the insects knowu as termites which build dwellings in part or in
whole above the level of the soil. The edifices erected by the tennites
are often 10 or 15 feet high and a score or more feet in diameter.
Although composed of earthy matter mainly taken from below the sur-
face, the hillocks formed by our common black ants which abound in
the temperate regions are not uncommonly from 18 inchej* to 2 feet in
height and of a diamet«r of from 4 to 5 feet. In the case of this
280 ORIGIN AND NATURE OF SOILS.
familiar species, the earth brought up from below becomes much inter-
mingled with leaves and twigs which may fall upon the hills from the
neighboring forest trees. (See Fig. 11.) As the mass of these hills is of
very incoherent material, it is subject to a constant washing from the
rain water, and so the material is gradually distributed over a wide circle
about the elevation. In some cases the sand accumulated in the hill
amounts to as much as 2 cubic yards in volume and when distributed
by the water it is of considerable thickness over a radius of 5 or 6 feet
from the center of the hill. Where these structures are numerous, as
they are in certain districts in the United StJites, by their constant
deposit of matter on the surface of the ground they bury a good deal
of vegetable waste in the soil; at the same time the animals are con-
stantly conveying int-o the earth large quantities of organic matter which
serves them as food and the waste of this, including the excreta of the
animals themselves, is of considerable importance in the refreshment
of the soil.
One of the most curious effects arising from the interference of the
ants with the original conditions of the soil consists in the separation of
the finer detritus from the ex)arse mineral elements of tlie detrital layer.
I long ago had occasion to observe that in certain parts of New Eng-
land, where the sandy soils had not for a long time been exposed tc the
plow or agents of tillage, certain fields were covered to the depth of
some inches by a fine sand without pebbles larger than the head of a
pin, while the deeper parts of the section, say below the level of a foot
in depth, were for a foot or so ftirther down mainly composed of peb-
bles of various sizes with little finer material among them. This dis-
tribution of materials was not to be explained by the supposition that
the original deposition led to the i)eculiar arrangement. It was easy
to see that the ancient order of the deposits must have been disturbed
by tillage, but it was clearly accounted for by the action of the ants.
These creatures to the number of tens of thousands on an acre are dur-
ing each season of activity industriously occupied in bringing the fine
sands and tiniest pebbles to the surface, thus taking away small mov-
able bits from among the coarser pebbles which they could not manage
to move. It is evident that this process would in the course of a cen-
tury bring about just such an arrangement of the fragmental matter as
we need to account for. (See Fig. 2.)
In genenil, the work of ants in the sandy soils resembles that of
earthworms in the clayey ground; both these groups of animals serve
to bring lower parts of the soil to the surface where it is more rapidly
subjected to the decay brought about by atmospheric action. As it is
fine materials which are best fitted for the duties of nourishing plants,
it is an advantage to the plants to have them brought near the top of
the grouiul, where the roots of ordinary vegetation may seize upon
them. In the work of the ants, however, we do not have that jieculiar
effect due to the characteristic habit of the earthworm, which takes the
8HALKB.] EFFECT OF BIRDS ON SOILS. 281
soil into its digestive ducts. Nevertheless, because tliey are much
more widespread thau their lower kiudred, these insects in the aggre-
gate produce a far greater influence on the soils.
Among vertebrated animals are a hundred species or more which by
their habits modify soil conditions. Although the number of kinds in
the backboned group of animals which occupy the soil is probably not
the fiftieth part as numerous as the list of insects which live for a time
or altogether in the realm of the under-earth, and the number of indi-
viduals is, it may be, not a ten-thousandth part as great, yet owing to
their relatively large size, the ground-haunting vertebrates exercise an
influence on the soils which is perhaps quite as great as that of all their
lower kiudred. This work of the vertebrates is effected in a great
variety of ways : by burrowing in the earth, by storing vegetable matter
underground, by overturning the surface of the soil in a search for food,
and incidentally by the contribution of their excreta during life and
their bodies after death, they greatly affect the conditions of the earth.
Some of the reptiles have the habit of boring in the earth, but their
excavations as compared with those made either by the insects or mam-
mals are of small importance. The most considerable work is done by
the various species of tortoises, which generally have the habit of going
under ground for winter quarters, and also to a certain extent in their
search for food, such as grubs. The large tortoise of the southern part
of the United States, commonly known as the gopher, makes consider-
able excavations, the exact purpose of which are not well known, though
they are accomplished with much labor. All of our serpents find in the
winter a refuge under ground, and although this is generally in some
decayed root or beneath a sheltering stone, the eflfect on the earth is of
some importance, because they frequently perish in their winter retreat.
A number of species of birds have the habit of burrowing to a certain
extent in the earth. A great part of these, however, use the earth only
as a place of shelter in their nesting time. The prairie owls, commonly
credited with the habit of burrowing, appear usually to usurp the exca-
vations formed by the so-called prairie dogs. It is not likely that the
owls have any share in the formation of the excavation which they fre-
quently inhabit. The bank swallows usually build their nests in a layer
below the level of the true soil in places where a stream has exposed a
steep face of the earth. The excrement of the parent birds and of the
young contributes a considerable amount of material to the earth in
which they dwell, and this store of nutriment may be sought by the
roots of the trees which grow in the superincumbent soil.
It is, however, only where the birds resort to some districts for breed-
ing puriK)ses that they considerably influence the chara€ter of the soil.
When, a few decades ago, the passenger pigeons existed in the Missis-
sippi Valley in very great numbers, they had the habit of nesting in a
gregarious manner, millions of them occupying the same tract of wood.
This area of timber they possessed for 2 or 3 months while they reared
282 ORIGIN AND NATURE OF SOILS.
their young. Feeding through the forests over a wide range of country,
and often extending their search for foo<l for 20 or more miles in every
direction from their roost, these swift winged creatures, able to fly at
a 8i)eed of GO or 80 miles an hour, supplied their young with food con-
veyed in their crop and sx)ent the night at the nesting place. The
quantity of the excrement voided by these birds on the ground beneath
the trees in which they nested was very great; at the end of the se^
son it often formed a layer of guano-like material over a district "per-
haps a thousand or more acres in extent. The result of this action was
after a few years to provide the under earth with an imixirtant store of
plant foixl ; at times the quantity of this material was so great as to
destroy the lesser vegetation by the manurial salts which, although
of utmost value to plants, can not be tolerated by them in excessive
quantity.
Where these birds resort in great numbers to a shore for breeding
they are sure to contribute a large amount of plant food to the soil. If
the rookery be thinly occupi(»d, as is generally the case with the eider
duck and some other water fowl, the sufficient but not excessive manur-
ing may produce a rank vegetiition which shows that the soil has a
profit from the contribution ; on the other hand, if the birds be crowded
together, the quantity of dung is generally so great as to destroy all
vegetiible life. When the breeding place is in an arid country, such as
that wherein lie the guano islands of the Pacific Oceiin or the Ca-
ribbean Sea, the accumulation of organic waste, dung, dead birds, egg-
shells, etc., is so great in quantity that it can not be in any degree
absorbed into the soil, but slowly accumulates and forms a coating
which may in time attain the depth of scores of feet. Although this
deposit can not in its pure state sustain any vegetable life whatever, it
affords in the guano of commerce the very best material for refreshing
soils which has been worn by tillage or for stimulating plants to very
swift growth.
Of all the vertebrate animals the mammals are the most eflTective in
their influence on the soil. Some hundreds of species have the habit
of burrowing in the earth and most of these forms spend a portion of
their lives under ground. It would reciuire too much spsice to trace the
extended variations of this habit in different species: we shall there-
fore only note its effects in the case of a few of our American forms.
The larger part of our burrowing mammals belong in the two groups of
moles and rodents or gnawing animals. Of these the moles are most
interesting, because of their pecidiar ways and the consequences of
their underground habits. The moles include the only mammals which
have adopted a purely underground habit of life and which, although
they occasionally come to the surface, are not compelled to emerge from
the ground for any organic purpose. They dwell for the most part in
the upper layer of the soil where they subsist mainly on insects. They
are accustomed to seek their food by extensive journeys through this
8HALKR.1 EFFECT OF RODENTS. 283
Buperficial portion of the earth which can easily be displaced by a bur-
rowing motion. They find their movements easiest and most profitable
in the layer of soil whic^h lies just beneath the roots of the grass and
other lowly vegetation, for there they can make their way partially by
pushing the earth behind them by the movements of their short stout legs
and partly by uplifting the surface in the familiar ridges which to the
eye mark the paths they follow. A single mole will in one season
break some hundred feet of these ways beneath the sod. Where they
find an abundance of focnl they \iall foiin a network of open passages^
so that the solidity of* the earth is materially aflfected by their action.
Between these selected feeding grounds, in which they wander deviously,
they form longer and straighter passages, utilized year after year in
their journeys to and from their regular haunts.
The effect of the movement of moles through the soil is to stir the
upi)er part of the layer somewhat in the manner in whicli this is effected
by the plow^ or spade. Sometimes for a season this action appears to
harm the plants whose roots are near the surface, yet on the whole the
delving work done by these creatures appears to be eminently profitable
to growth. It stirs the soil about the roots and favors the entrance of
the air.
There is, however, another effect from the mole burrows which is not
so advantageous. We have already noticed the protective action of
vegetation which serves to greatly diminish the erosion accomplished
by rain water upon the incoherent matter of the soil. The mat of super-
ficial roots and the coating of decaying vegetation makes it difficult for
the water to gather into distinct streams and yields the fluid gradually
to the large brooks. When a mole burrows beneath the layer of mold,
or the roots of the sward descend a steep incline, the water is likely to
enlarge the channel so that it becomes open to the day and may develop
into a deep ravine. In this manner the moles in certain districts favor
the degradation of the soil coating and their action in this regard is
often extensive and important. Owing, however; to the large part
which these creatures play in the destruction of insects that prey upon
the roots of plants, as well as to their activities in stirring the soil and
opening it to the air, their general influence must be regarded as bene-
ficial.
The greater part of the rodents — an order which includes more species
than any other order of mammals — ^to a greater or less extent dwell
underground; by far the greater portion of these, however, unlike the
moles, derive their subsistence from the overground vegetation or from
the roots of plants, resorting to the earth mainly for protex»tion from
their enemies or from the winter's cold. Some of these, as for instance
certain species of field mice, dwell almost altogether beneath the sur-
face, resorting to the open air only for such food as the plant roots fail
to afford them; others, such as the hedgehog, habitually resort to their
burrows in summer only for sleej), although in winter they occupy them
284 ORIGIN AND NATURE OF SOILS.
during a period of »ome months. In certain parts of the country,
notably in regions where weasels and other small predaceous mammals
are absent or rare, the species of field mice exists in amazing plenty.
Thus on the island of Marthas Vineyard, Massachusetts, the wild mice
are so abundant that brushwood areas, often acres in extent, are com-
pletely honeycombed by their burrows, and many species of plants
whose bark affords nutritious food in winter are almost extirpated by
their attacks. All these species of rodents which dig underground
shelters have a notable influence on the soil; they drag out the earth
which fills those places and heap it at the mouth of the openings, and
in this way they turn over a great deal of the soil and mingle the vege-
table matter with the mineral material. A burrow affords an easy and
extensive passage for rain water, and when the occupant deserts it it
becomes filled with decayed leaves and other vegetable waste, and
thereby much organic matter is mingled with the earth.
The underground habits of field mice serve to hide the measure of
their activities from even the observant eye. A good conception as to
their numbers and the extent to which they may affect the earth may
be formed by a simple observation which can readily be made in any
regiim where the snow accumulates in considerable drifts. It is the
habit of these creatures to resort to the surface of the earth beneath the
snow banks, especially where these accumulations lie upon grassy
ground. Gathering to the number of hundreds in these parts of the
surface where they are well sheltered from the cold by the thick
nonconductive covering, they construct an amazing tangle of bur-
rows cut in the sod and roofed by the snow. These excavations seem
to be made in a certain order, mainly to procure the food which the roots
of the plants afford. In certain places, particularly in the Berkshire
Hills of Massachusetts, I have observed that, in addition to the narrow
runways, each wide enough for the admission of one uidividual, they
also make considerable clearings, sometimes as much as a foot across,
which seem to serve as assembling places, where, crowded together, they
may indulge their social instincts and perhaps help each other by their
mutual warmth. Where field mice are abundant the skillful observer
may with a little care in removing the superficial coating of vegetation
disclose the burrows thus formed. These usually lie in the upper 6
inches of the earth, and are often so abundant that over extensive fields
no square foot can be found which is not intersected by them.
All the species of wild pigs have the habit of uprooting the upper
part of the soil layer in their search for seeds, nutritious roots, and grubs.
Where these pachyderms abound they turn over the top soil often to the
depth of several inches in a singular way, and by so doing they mingle
decayed vegetation with earth. One individual of this group will in a
year turn over an acre or moreof any ground which tempts him to exercise
his strength upon it. Various other mammals and some birds also have
the habit of scratching or pawing the earth to obtain food. Some spe-
sHALEu.l EFFECT OF ANIMAL REMAINS. 285
cies wallow in the mud or in dry soil, seeking thereby to kill the insects
which infest them. Various forms of the larger herbivora have the
habit of resorting to dry ground, which they toss up into the air with
their feet so as to dust their bodies with the powder. The stamping
grounds of the ancient bison or buffalo of this continent were once fre-
quent and conspicuous features in the regions which they inhabited, and
the beasts can still be traced, even in Kentucky, from which they were
driven more than a century ago, in the fields thick set with the curious
ragged pits long ago excavated.
While we are considering the beneficial eflFects upon the soil brought
about by animals which have the habit of conveying fertilizing matter
to the earth or of overturning it, we may note the partly injurious
influence which the beaver exercises in the country where it abounds
through its curious custom of building dams across streams. When this
continent was in its primitive state these rodents, the largest of their
kind, occupied with their habitations the valley of almost every small
stream of tolerably gentle declivity. At each of these beaver lodges
there was a barrier or dam a few feet high which they constructed across
the brook. This held back the waters of the pond, which had an area
ranging from a few square rods to many acres in extent. On the line
of a brook these dams were often placed one above the other in tolerably
close order to the number of dozens. The result was that a great deal
of the level land near the water ways was inundated when the white
man came to the country. Until these creatures were extirpated or
driven to seek secluded places by the incessant pursuit of hunters and
so were forced to give up the habit of dam-building and until the
structures which they had erected had been removed by decay or by the
hand of man, it was almost impossible to journey through many valleys
which are now moderately dry. The influence of the dam-building habit
of the beaver was not altogether prejudicial to the soil, for the reason
that while the swampy places they created were unfavorable to soil-
making, they served to restrain the descent of the flood waters, and thus
in a measure spared the greater rivers the inundations to which they
were subjected after these industrious creatures were expelled; more-
over, their reservoirs served to retain the soil materials brought down
by the mountain torrents and thus diminished the waste of the precious
material to the sea.
All the vertebrate animals of the land when they die leave the precious
store of nutriment contained in their bodies as a heritage which is sooner
or later to come to the soil; in the greater number of cases this waste
immediately goes to satisfy the hunger of other wild animals, but the
smaller forms are generally buried by the carrion beetles and the bones
of all are left to decay on or in the ground. In time these hard parts
are dissolved by the water and conveyed to the roots. The quantity of
nutritious bone dust which is thus contributed to the earth is, when
measured in terms of geologic time, very great. If all the skeletons of
286 ORIGIN AND NATURE OF SOILS.
vertebrates which have thus gone into the soil since the close of the last
glacial i)eriod had remained uiKin the surface they would probably cover
the land with a layer of bony matter some fe<»>t in depth, but the return
of this material is so rapid and constant, that it is rare that the observer
remarks the presence of bones in the wilderness places. '
Before leaving these considerations as to the eflFect of organic life on
the soil, we must study the acttion of certain peculiar groups of lowly
creatures known as bacteria, forms which are classed as of a vegetable
nature and which are in general somewhat related to the ferment of
common yeast. It is only of late that naturalists have begun to inves-
tigate the members of tliis group, for they are among the lejist visible
things of the world 5 yet it is already determined that they play a
very large part in the life and death processes of organic bodies. It
is now known that they are the cause of most malignant diseases; they
are also active in the process of digestion. Recently their operations
in the physiology of the soil has received some attention; it has been
found that they exercise an important influence on its economy. Thus
the processes by which the nitrates of potash and soda are formed in
the soil is believed to be due to the action of bacteria. The precise
chemistry of the action is not yet well understood, but this is not a part
of our inquiry. The result is of the utmost imi)ortance to the soil
processes, for the fertility of the latter depends upon it to a considerable
extent. In regions of ordinarily abundant rainfall these nitrates, being
very soluble in water, are rapidly removed from the soil. While the
solution is passing by the roots of plants the nitrogenous matter is
seized upon and the rest escapes through the streams or else, by de-
composition, is returned to the air. When, as in the arid lands of
southern Peru and certain other parts of the world, the rainfall is only
enough to nourish these creatures and not sufficient to leach away the
nitrates, they accumulate and form a deposit so large in quantity as to
be of great ecx>nomic importance. Like other materials we have men-
tioned, which in small quantities are very helpful to plants, but in
excessive proportions are very hurtful, these nitrates destroy the fitne^^s
of the area where they abound for the ordinary uses of vegetation.
These nitrous soils are the source whence are derived the salts required
in the manufacture of gunpowder as well as in many other important
arts.
The supposed influence of the microbes in the production of nitrous
soils is a matter of great interest, for the reason that thus far no other
explanation as to the ways in which the nitrogen of the atmosphere
can be brought into this form has been found. Should it be clearly
proved that this important action is due to organic life, it will add
greatly to our conception of its work in the processes of the earth.
In this fiirther discussion of the soil problems it will be necessary
somewhat to rei)eat the discussion of certain points which have pre-
viously been considered. As the points of view are ditt'erent from those
8RALBR.] EFFECT OF GEOLOGIC CONDITIONS. 287
taken before, it will be better to restate some of the facts here than to
refer the reader to the previous sections of this essay.
We have now considered, at least in a general way, the effect of
animals other than men on the formation and preservation of soils.
Our own si>ecies has in its civilized condition invented a set of relations
with the earth the like of which do not exist in the case of any other
being. It will, however^»well for us to consider the effect of human
agencies on the soil coating after we have completed our study as to the
geological phenomena which influence it. In this domain of our inquiry
which now ox)ncems us there remain for presentation the conditions
dependent on the passage of water through the soil and those arising
from the varied nature of the rocks from which the mineral elements of
that coating have been derived. We have also to note the diversity
and character of the earth due to the extent to which the materials of
which it is comi)08ed have been derived from rocks immediately under-
lying the particular area or have been, as is the case with alluvial de-
posits, brought from a distance by the action of various transportative
agents. These questions will form the subject-matter of the next chap-
ter, and wiU complete our rapid study of the general physiology of soil
deposits. It. should here be noticed that so far our inquiry has con-
cerned only soils whose mineral parts are directly derived from rocks
which lie beneath a given area. We have now to consider certain
classes of soil deposits which are of a different origin.
EFFECT OF CERTAIN GEOLOGIC CONDITIONS ON SOILS.
When the soils of a country outside of the ghudated districts lie
ux)on bed rocks of gentle slope the mineral materials of which they
are composed have generally been derived from deposits immediately
beneath the surface. Although a considerable part of the soils of the
earth belong to this group of accumulations of nearly horizontal attitude
and therefore of immediate derivation, the larger part of them are more
or less affected by the presence of substances imjwrted from a distance,
and probably much more than half the total soil areas of the earth have
their mineral detritus composed of materials which have journeyed from
afar and so may be classed as deposits of remote derivation. In this
class come all the glacial soils the mineral matters of which have always
been conveyed from a considerable distance. Here we must also place
the whole group of soils which have been formed by the floods of rivers
bringing sediments from the torrent portion of their drainage systems
to the lower part of tlie valleys in which they lie. All this tran8X)orta-
tion, except the small amount which is affected by winds, is substan-
tially due to the action of water either in its frozen or fluid form descend-
ing from the highlands to the sea. This carriage of soil detritus is
accomplished by the action of solar energy, which is applied in the form
of heat in the manner already traced. In most cases this carriage is
effected by fluid water, but it is sometimes brought about by glacial ice.
288 ORIGIN AND NATURE OF SOILS.
GLACIAL AOOREGATION.
When the transportation of rock detritus is brought about by ice and
the materials are deposited in the form of till or bowlder clay, the
result generally is that the mineral components of the soil are in their
chemical nature far more varied than where they are derived from rocks
which lie immediately below that layer, Mk,use the ice carriage is
eflfected under conditions which tend to minpe on a single square mile
of surface the detritus worn from an area of ten or more square miles.
On the other hand, where the glacially transported detritus has at the
end of its journey been assorted by water, as is the case with much of
the drift, the sorting action usually gives a singularly uniform character
to the detritus found in any particular area. We then note that the
material which the vegetation seeks to convert into true soil consists in
the main of pebbles of sand or of clay, each with but trifling admixture
with the others. The result is that the unassorted bowlder clays, even
where very stony, generally afiford fertile fields moderately well fitted
for the needs of a great variety of crops and quite enduring to tillage.
These bowlder clay soils are apt to have a fair share of all the elements
which are demanded by plants. On the other hand, the stratified drift,
because it is composed mainly of one kind of rock material, often a£fords
nothing like the variety of constituents required by varied crops.
In New England, where the white settlers at first selected stratified
drift areas for tillage for the reason that they were not encumbered
with bowlders, it was soon found that such sandy soils, though easily
made ready for the plow, were quickly exhausted and could be brought
to yield fair crops only by extensive fertilizing. The greater part of
these sandy soils have been abandoned, and people have resorted for
plow land to the areas which are underlaid by bowlder clay. Such
fields, though stubborn and demanding a great deal of labor to clear
away the bowlders, are very enduring to tillage, because by the slow
decay of their pebbles of varied mineral constitution there is constantly
yielded to the soil something of the substances required by the diflfer-
ent crops. The observer readily observes the fertilizing effect arising
from the decay of bowlders in the soil indicated by the belt of exceed-
ingly fertile earth accumulated in the form of a narrow strip around the
base of tlie great erratics in New England pastures. We have already
noted this feature in a previous chapter, but it is worth reiterated at-
tention.
ALLUVIAL AOOREGATION.
Another class of soils of remote derivation is found in alluvial plains
which border nearly all true rivers. The history of this group of detrital
deposits is so important that it should be traced in some detail. To
understand the formation and the physiology of alluvial soils we must
begin our inquiry in the torrent sources of the river and observe what
takes place in these fields where the debris of which alluvial deposits
sHAiiB.] ACTION OF TORRENTS. 289
are composed is broken from the bed rocks. In this mountainous sec-
tion of a river system we find that the slopes bordering the streams
are generally very steep and bear but a scanty coating of detritus.
Owing to the action of frost, rain, the expanding roots of trees, and of
other inorganic and organic agents which aid gravitation in urging
the incoherent mass down the incline to the channels of the stream,
this mountain soil covering is in tolerably continuous motion toward
the torrent beds. When the slopes are very steep the movement is
often sudden, in the manner of avalanches or landslides; when the de-
scents are less precipitous the motion is gradual but inevitably to the
same end. At the base of the converging slopes which form both
sides of the mountain valley the torrent is ready with its swift currents
flowing down the steep slope to seize on aU the detritus which is brought
within its grasp; it urges the debris downward to the lower levels of
the country. Unless the fragments of stone are very large they are
hurried down the declivities in the times when heavy rains have swollen
the brooks; beating against each other and against the rocky bed and
sides of the channel the debris is constantly reduced to fragments of
smaller size and thus becomes more readily transportable. In nearly
all cases, however, the diminution in the size of the fragments is less
rapidly brought about than is the reduction of the carrying power of
the stream, which diminishes with the decline in the declivity of the
descent. It is asserted by those who have careftiUy studied the subject
that the capacity of a stream for conveying fragments of stone is in
proportion to the sixth power of its velocity; although this is perhaps
an excessive estimate, it will serve to show how rapid is the diminution
in the ability of a stream to convey coarse detritus when its current is
much slackened. (See Fig. 17 and Pis. xxiii and xiv.)
As the torrent emerges from the higher parts of the mountain district,
where its rate of descent has generally been from 100 to 500 feet to the
mile, and comes among the foothills of the range its fall usually dimin-
ishes to from 20 to 50 feet to the mile. The consequence is that the
speed of flow of the water is rapidly slackened and it can no longer urge
forward stones which it easily bowled down the steeper slopes whence
they were riven.
We can note the growing incapacity of the stream to dispose of the
debris which it bears if we follow down any mountain torrent until its
waters pass out upon the plain land where lies the river system into
which it discharges. In the steeply descending portions of its upper
path there is no margin or border of debris which is at rest on either
side of the stream. Except here and there wliere some large mass of
rock has become wedged in a narrow channel, all the materials on the
mountain slopes and in the bed of the torrent are in times of flood in
more or less motion toward the lower levels. When in descending we
come to where the valley widens and the speed of the waters is lessened
we notice that the larger stones even in the flooded state of the brooks
12 GEOL 19
290 ORIGIN AND NATUR£ OF SOILS.
are left stranded on the side of the channel where the current is less
swift. If there be space for the accumulation between the stream and
the neighboring steeps these fragments that are too large for the current
to carry onward will fonn a little margin or terrace, the surfiice of which
speedily becomes occupieil by vegetation. Examining this mass, we
find that it is essentially comimsed of large stones more or less rounded,
the interstices to a certain extent tilled with smaller pebbles and sand.
This liner material luis been IcKlged in the spaces when the waters have
risen above the surface of the rough plain. (See Fig. 12 and PL xxv.)
Following down the stream, wliich, owing to the constant lessening
in its rate of fall, is rapidly diuunisliing in the energy of its flow, we find
that these detrital plains usually incre^ise in extent, and are comi>osed
of finer and finer materials the farther we pass from the torrential system.
When we attain to the true river section of the drainage where the
Fio. 12.— Section through tbo ooune allavium formed beside a torrent bed. a, terrace.
stream flows smoothly with a descent of from 6 to 18 inches in a mile,
the alluvial plains usually widen and exist on both sides of the channel :
here we find the debris to consist of very fine gravel, coarse sand, and
clay, the latter being in relatively small proi>ortion. If the lesser river
finally passes into one of the greater streams, such as the Mississipjii,
we observe that there is a progressive diminution of slope as we approach
the sea until the decline amounts to no more than about half a foot to
the mile. In this part of tlm river system the alluvial fields are very
wide and the detritus of which they are composexl is very fine gniined,
the greater part of it almost impalpable mud, and the few pebbles which
occur rarely in size exceed a tenth of an inch in diameter. (See Figs. 13
and 14, and PI. xxvi.)
The student who is observing the alluvial plains quickly notices that
these masses of detrital materials are in constant course of destruction
and renovation through the action of the river which built them. On
the convex side of the great sweeping curves through which tlie stream
marches the speed of the water is slackened and a portion of the sedi-
ment held in solution is laid down in the shallow water next the shore.
Generally this debris is deposited in time of flood in the spring of
the year. No sooner do the waters recede than certain plants of
swift growth, which find their appropriate conditions on the verge of
the river, extend their roots through it and cover it with their thick-set
8HALEE.] AREA OF ALLUVIAL SOILS. 291
stems, aiid thus bind the iiew-intule land firmly together. By this ac-
tion a single flood may add a strip of land to the margin of the convex
shore having the width of some score of feet, a length of several miles,
and a depth of a foot or more. The next rise of the waters may find
the willows, cottonwoods, and other water-loving plants growing
thickly over the surface of tlie new-formed ground. The turbid water
entangled among the stems has its current slackene<l, and another de-
posit of alluvium is laid down. Thus in the course of ten years the ter-
race nuiy have risen to the height of 10 or 15 feet, and may be so far
united to the general mass of the river plain that the process of its
growth and its re<5ent origin are not discernible. (See Fig. 14.)
When land is making on the convex side of the bank where the cur-
rent is relatively slow, it is commonly wasting on the ojiiwisite side of
the river against which the stream is impinging with swifter motion.
Here it cuts away the alluvijil matter which it has laid down in some
previous state of its history. As the material falls into the flood many
of the fragments formerly deposited because they were too large to be
carriwl any ftirther in the waters at the speed attained may be ob-
served to fall to pieces, owing to the chemical decay which has come
Fio. 13. — Section across a river valloy showing terraces of alluvium, a a, bed rocks; b b, upper older
terraces ; c c, lower newer terraces ; d, low-water level of river.
upon thein during their repose in the alluvial plain. Much of the finer
matter is so far oxidized tliat it can reiidily be taken into solution and
borne away to the sea. The insoluble fragments are carried farther
down strejim until they attain a phK*e like that before described, where
they may again be built into the terrtice. In this manner, cutting away
the alluvium in one place and building into the bank at another, the
river gradually swings to and fro over the whole width of the valley
floor, slowly but continually destroying and rebuilding its marginal
plain. Inasmuch, however, as in most cases the stream is steiidily deep-
ening its bed, portions of the old plain are occasionally left on the side
of the valley above the level to which floods attain ; sometimes these
ternices lie at a considerable height above the latest level of the water,
even in its time of flood. (See Figs. 13 and 14.)
The total area of these alluvial soils on this continent is probably over
200,000 square miles; of this the greater part is subjected to occasional
overflows, not sufficient to destroy its value for tillage, and a small por-
tion, perhaps one-tenth of the whole, consists of terraces not liable to
inundations. The physical conditions of this interesting class of soils
formed on alluvial plains are peculiar. Like glacial dex)osits, they fall
292
ORIGIN AND NATURE OF SOILS.
into the class of materials which we have termed of remote derivation,
that is, they are, for their mineral ingredients, not dependent on the bed
rocks which underlie them, but are in this regard conditioned by the
nature of the deposits in the upstream districts whence the river drains.
In any one acre of alluvial soil on the banks of the lower Mississippi we
may reasonably believe to lie some bits of rilatter which have been derived
from every considerable field of the surface drained by the river above
the point where the deposit lies. Thus, as regards their mineral mate-
rials, and to a certain extent also a« regards their organic matter, river
deposits are more composite in their nature than those originating in
any other manner. Like glacial soils, they represent the waste from over
a considerable area, but for the reason that the ice sheet, at least in its
continental form, moved in a somewhat rectilinear manner while the
streams of fluid water flow convergingly, alluvial x)lains have generally
drawn waste from a far wider field than the glacial accumulations (see
Fig. 14).
Fio. 14. — Section acroes aUavial pUln on one side of a largo river.
While glacial waste, owing to the lack of oxidizing agents in the ice
or in the water which is produced by its melting, is generally unde-
cayed, the material deposited by the river is usually somewhat advanced
in decomposition when it is laid down. The conditions of this deposi-
tion tend to bring about a mingling with the mass of mineral matter of
much vegetable and some animal waste. These int.erbedded organic
materials, as we have already seen, serve greatly to promote the changes
which lead to the solution of mineral matter in water, and its appropri-
ation by the roots of plants. We may indeed consider these deposits of
river-borne waste as admirable natural laboratories in which the great
work of dissolving mineral substances is carried on. The gases en-
gendered by the decay of organic materials favors this rotting action,
and the porous character of the deposit permits the rainwater to pass
freely through it. By so passing the water brings the soluble materials
into a condition in whicli they may be appropriated by plants or flow
forth with the drainage into the neighboring stream and thence to the
sea.
Alluvial soils, at least when first subjugated, have in general a high
average fertility. The variety in this regard is greatest in the deposits
formed beside the banks in the headwater district of a river system, for
in these situations the local peculiarities of rock in particular districts
have a dominating influence on the chemical nature of the mineral
I
8HALBB.] ACTION OF BAIN WATER ON SOILS. 293
elements of whicli the terraces are eonii)08ed. In snch an alluvial dis-
trict as that of the Lower Mississippi, where the detritus represents an
average of the waste from the whole of the great valley, there is
naturally a greater uniformity in the character of the materials; yet
even in this district there is a certain diversity due to the sediments
brought in by the tributaries which join the main stream near the site
occupied by the alluvial fields.
Soils of this nature are also liable to modifications due to a variety of
special conditions. Where covered by vegetation, as is usually the case,
and where visited by floods in the rainy season of each year, the current
of the turbid water, having been checked by the resistance which the
friction of the vegeta-tion offers to its motion, dei)osit8 a layer of fine
mud on the surface and thus affords refreshment to the soil. When a
similar flood passes over open lands the motion may remain so swift
that the most of the fertilizing matter suspended in the water will be
carried forward, and only the coarse sand deposited, which is of little
value to plants. In general, however, alluvial lands have proved them-
selves to be the most continually and largely productive of all the soils
which have long been taxed by tillage. This endurance to the demands
of agriculture is doubtless to be attributed to the great depth of the
thoroughly oxidized materials which compose these deposits, to their hor-
izontal position, which insures them against the risk of washing away,
and to the fertilizing inundations which frequently visit then.
We shall now turn somewhat aside to consider the action of the water,
which, after performing the important underground work which we have
traced in preceding chapters, escapes from the soil, joins the streams,
and passes in them to the sea. We have seen that all organic life de-
pends upon the peculiar capacity which water has for taking a great
variety of substances into solution. It is hardly too much to say that
the truly vital parts of animals and plants are solutions containing that
portion of the soil which is in condition to enter into living forms. The
frames of such animals are built up of material which has passed or is
ready to pass into the dissolved state. The insoluble x>ortion of the
soil mass is essentially without eflfect on life, except as a reservoir of
water and a laboratory where the materials are preparing for the state
in which they may be vitalized.
When rain water departs from the soil it bears away with it more or
less mineral matter. Evidence of this may be had by the simple ex-
periment of completely evai)orating a pint of water taken from the rain
before it has touched the earth, and at the same time another equal
quantity from any spring which drains from an ordinary soil. At the
end of the experiment we find that the rain water leaves little or no
residuum except possibly a few bits of matter which, floating as dust
in the air, has been caught in the falling drops, while the soil water leaves
a layer of sediment on the bottom of the vessel. Analysis shows this
material to have been derived from substances in the soiL A familiar
294 ORIGIN AND NATURE OF SOILS.
inAtance of this action may be seen in a teakettle the water of which is
supx>lic<i from a spring or well ; after a time a crust will be found in the
bottom, composed of the mineral matter originally held in the water,
which has gone away in the form of steam.
The mineral matter dissolved in the soil is first offered to rooti^i which
in most cases plentifully interlace the path along wiiic^h it escapes to
springs and thence to streams. Each year the share of rain water
which finds its way into the soil, amounting on an average to about 2
feet in total depth, goes through that layer and flows to the sea after
gathering a considerable share of mineral matter. The amount of solid
material suited to the needs of jilants which is thus each year withdra\^Ti
from the land and given to the ocean is very great. It is jirobably in any
one season nearly as much as is taken from the soil and built into the veg-
etation of the forest, and even that which enters the vegetation is but
temporarily beyond the reach of this danger, for when the i^Iauts decay
the mineral material is again ready to be dissolved.
At first sight this great excurrent tide of fertilizing material may
seem to be a most unfortunate feature in the economy of the earth, but
on closer consideration we find that the api)arent loss is not real; the
process, indeed, when considered in a large way, is seen to be of a con-
servative nature. The mineral matter which is taken from the earth
by the percolating ground water is first turned to good account in sup-
plying the roots of plants; when it has served these needs it is neces-
sary that it should be drained away, for it would becx)me charged with
a deleterious excess of substances which are taken into solution, and
which, if retained in the soil, would be injurious to vegetation. An in-
stance of this is familiar to persons who have kept plants in pots. It
is well known to all who have had the care of potted plants that it is
necessary to provide for the ready escape of the water from the vessels.
Some of the effects of an insufficient passage of the water through the
soil may be observed in swamps, and will hereafter be noted in con-
nection with observations on the arid land of the Cordilleran district
and other places where the rainfall is not sufficient to provide the
normal current of water through the soil. Although it is necessary
for the plant to have a certion amount of mineral matter in the water
which bathes its roots, any excess of such material appears to i>rove
poisonous. When the water becomes saturated with the substances
it may dissolve, even ti) the extent to which the sea is so charged
with such materials, the effect on plants is generally destructive.
When water escapes from soil into rivers and goes thence to the sea
it bears with it the mineral matter which it has in solution, and on en-
tering the ocean becomes mingled with a great store of such substances
which the deep holds in its keeping. We are in part made aware of
this charge of dissolved mineral matter by the evident salinity and hard-
ness of sea water. In this great storehouse of oce^n it has been fimnd
by careful chemical tests that there is a share of the mineral substances
8HALEB.] ACTION OF SEA WEEDS. 295
contained in soil water. In fact, practically all the elementA which exist
in appreciable quantities in the crust of the earth and a great variety
of the comi)ound substances which enter into organic forms, such as
lime carbonate, potiish, soda, etc., are known to exist in a dissolved
state in the ocean waters. It is probable that in them is contained a
variable proi>ortioii of every element which exists in the earth. From
this great reservoir of the sea the marine plants, eiich after its kind,
extract substances, appropriating them through their fronds in the same
manner as the land ])lant;S take their share by means of the roots in the
soil, but i)orhaps in greiitcr variety. It may again be noted that, as sea
weeds have no roots, the whole of their surface serves for this puriK)se
of absorption, whereas in land plants the roots alone have thisiK)werof
appropriation.
Sea weeds, like land plants, are mediators between the mineral realm
and the animal kingdom. Animals are altogether incapable of taking
mineral substiinces dirwtly from the water; they appropriate them only
at second hand, by feeding on the vegetation or on other animals which
have obtaine^l them from vegetation. Although at first sight marine
plants appear, on account of their usually small size, to occupy a limited
place in the sea, the volume of their life is vast; they grow rapidly, they
appropriate mineral substances which are brought to the ocean waters,
and so feed upon the materials which are placed in solution through the
action of the land vegetation. Thus in a simple and tolerably direct
way the removal of mineral matter from the soil serves to provide ma-
rine life with the necessary basis for its development.
There are other and important, though remoter, eflFects arising from
this vast and ceaseless transfer of the minerals of the earth to the sea.
The marine plants and some of the animals have the habit of appro-
priating large quantities of si>ecial substances, such as iron, lime, potash,
soda, etc., and even particular metals, such as silver; and on certain
fields of the sea floor, where the remains of marine vegetation are built
into strata, the sea weeds form deiK)sit8 remarkably rich in these elements
which they appropriate during their lifetime. Thus the coral animals
build great islands in the ocean and vast fringing and barrier reefs
along the shores. The limestone of these creatures is derived from the
store of that material which is dissolved in the land waters, mainly by
virtue of the carbonic dioxide arising from decaying vegetation, and
which is brought by rivers to the sea. In each cubic foot of this lime
of the coral reefs it is likely that we could find, if we had the means of
as(^ertaining the fticts, one or more molecules derived from each of the
river bivsins of the earth. So incessant has been this process of change
that it is also probable that every cubic foot of limestone now lying in
the beds exi)osed on the land contains elements which in their previous
wanderings have journeyed through every sea, which have been in turn
built into strata in all the quarters of the globe.
Wbeu animals possess, as many of them do, the habit of secreting in
296 OBIGIN ANU NATUBE OF SOILS.
their skeletons or Rhells such importaat substaaces aa lime pliOApbat«,
perbajiK the most uecessary of all the soil substances to the develop-
ment of crops, the beds which are formed of their remains often afford
most fertile soils. Thus in centml Kentucky, where the soil of the
country has an uncommon fertility and endurance to tillage, its ([uality
is mainly due to the presence in the limetttone beiLs wbicli underlie the
area of certain layers peculiarly rich in phosphoric aeid. Some of these
strata, from a few inches to a foot in thickness, eontain from 10 to 20
I)er cent of lime phosphate, and aa these portions of tbe horizontally
lying roi^ks deejay the fertilizing material is carried dowu the sloi>e8 of
gently inclined hills and, dissolved in the soil water, is made free to all
the jdaute. (See Fig. 15.) It is hardly too much U> say that in each kernel
of which wheat or other grain is temporarily stored the molecules of lime
Flo. 15 DUgnm si
phosphate which have been brought together by the action of animal or
vegetable life on the seafloor. Our civilization in good part rests upon the
grains we win from tbe field. It would not be possible, therefore, to main-
tain the status of higher men without the compact aud nutritious foods
which we thus obtain.
In the above considerations concerning the origin of soil fertility we
have naturally found our way to a division of the subject in which we
are to consider the effect of the diverse character of underlying rocks
uiwii soils which are formed by their decay. The range of faets which
will I.AVC to be explored in order to make a survey of the whole of this
field is 80 great that it will he necessary to limit our undertaking to
certain characteristic instances which may serve as types of the condi-
tion, leaving the reader to make his own application of tbe principles
we thus acquire to the particular ctises which he may need to explain.
First of aU we note the fact that the classification of soils as regards
their mineral constituents into those of immediate and those of remote
deri<"ition, while true in a general sense, needs a certain amount of
qualification.
OVEItPl.ACBMENT.
Almost all soils except those on very level plains have derived their
mineral parts in some mestaure fnim the rocks wliich <lo not lie imme-
diately beneath their site. In the glaciated districts as well as those
«HALBB.] MOVEMENT OP SOIL DOWN SLOPES. 297
covered by river alluvium the transportation of mineral elements is
from distant points and is in a way complete. In other soils, which
may in general be accounted of immediate derivation, where the surface
has a considerable slope, a certain migration of the detritus is brought
about by the slipping of loose earth over the surfaces on which it lies.
As already noted, this action is tolerably constant and may lead to
journeys of the disintegrated rock for distances of a mile or more. Dis-
tinct evidence of this movement may often be found where a hilltop is
capped by some layer of enduring rock, while its slopes are underlaid
by a looser deposit, such as clay. In such a condition of the surface we
often find masses of the capping layer which have separated from its
steep face and liave slowly journeyed down the incline below until they
have attained the bed of the neighboring stream. (See Fig. 16.) It
is easy to prove that these masses, which are often many hundred
cubic feet in contents, have journeyed slowly over the distance they
have traversed and with a very uniform motion, and not suddenly, as in
the manner of a landslide. Examining the procession of blocks, we see
Fio. 16.— Diugrain showing the dirtMStion aad the rate of motioii of boU. a a, soil; b b, bed rock. Tlie
arrows show by their relative length the rate of movement at various points.
that they have not been overturned, but that they generally lie substan-
tially in the position of their original bedding. We also note a gradu-
ally and progressive decay of the fragments as they lie farther down
the slope. Kear the cliffs whence they came they have sharp fauces and
are very little decayed; a few hundred feet from the escarpment they
are more rounded and the decay has penetrated deeper; near the stream
they are often so rotten that when they actually attain the torrent bed
they are easily broken up by its swift-moving waters. These facts con-
firm the conclusion that the whole of the soil layer is in gradual motion
down the slope on which it lies. In this movement it is impelled by
gravity abetted by frost action, the expansion of roots, the overturning
movement of uprooted trees, and the burrowing work of a host of animals.
Excellent examples of this movement of soils down the declivities
bordering a stream are afforded by the descent of blocks of stone from
the hilltops in almost all districts where horizontal strata underlie the
surface of a country. It is indeed usual in such regions for the harder
layers to crown the elevations, for the simple reason that such beds, by
resistance to decay, determine the position of the hilltop. Perhaps the
best instances of this in this country are exhibited in the region occu-
pied by the Millstone grit or the thick conglomerate which lies at the
298 ORIGIN AND NATURE OP SOILS.
base of the Coal Measures. These beds often rest upon shales and form
steep cliffs, such as are found along the western escarpments of the
Appalachian coal field. Fragments from those cliffs, sometimes as large
as an onlinary house, may he observed j<mrneying down the inclines to
the streams. They oft4»ji bear trees and are surrounded by and partly
imbedded in tint soil. Less ex)iispicuous instiinces of the ssime nature
may be tracexl in almost any upland country south of the glaciated
region. (See Fig. 17.)
Besides the migrations of mineral matter brought about in this man-
ner, there is on steep slopes a constant movement of substances held in
solution by the ground water. This w^atc»r, creeping do>vn the hill with
its charge of dissolved material, serves to qualify the charact-er of the
nourishment afforded to pbin ts by the substances extract^l from the imme-
diately subjac^eut rock. It thus often hapi)ens that the presence of a layer
Fio. 17.— Biai^niin nhowinf? profn^AH of fragments down a Hlopo t-o a ntroam. a a, liod of hard rock;
b b, Tngiaenia movinj^ down Rlopc.
of fertilizing material nejir the summit of a slope will serve to enrich the
soil for a great distance down the incline. Thus in central Kentucky the
layers of phosphatic limestone, even though their fragments do not slip
down the hill, will be found to have effected the fertility of soil derived
from rocks barren of nourishment which lie farther down the declivities
in which the enriching layers outcrop. In this way, though the partic-
ular beds which afford the important mineral element may be so soft
that they yield no tragments to the detritus below their level, the effect
is almost as valuable to plants as where they contribute to the visible
debris. It is a fiict worthy of note that owing to this movement of
materials down the sloi>e the substances derived from a x^articular kind
of rock may affect the soil at some distance below the site of the layer
rather than that which immediately overlies the bed ; the outcropping
edge of the rock deiwsit may itself be covered to a considerable dei)th
by the barren debris derived from beds which lie higher up the declivity.
The mode of tliLs action is indicated in Fig. 15.
Where, as in the case of hillsides sloping steeply toward the stream,
the motion of the soil is rapid and the torrent at the base sufficiently
powerful to wjish the ddbris away as fiist iis it comes to the channel, the
soil material may be so s]ie<»dily removed that it does not a(*cumulate in
a thick layer, and so the chemical processes do not have time to bliug
SHALEB] SOILS IN MOUNTAIN VALLEYS. 299
the debris into the state where it may be taken into Molutiou. Such
slopes are often in the main covered with a nibble of angular fragments,
mingled with a little true soil, which supports a scanty vegetation, the
condition of the debris showing plainly the lack of sufficient time to bring
the rock waste into the finely divided state in which it may be appro-
priated by the roots. If in a valley exhibiting these conditions, which
may be said to be normal in mountainous districts, as well as in many
countries where the hills are steep, we penetrate to the hejuiwaters of
the stream, where its dwindled torrents are not able to bear away the
detritus which marches down the 8loi>e, we find very different soil con-
ditions. In these "coves," as they are termed, the soil is often very
de«p and of great fertility.
In the stiite of nature the difference between the soil in the lower
and the upper parts of a mountain valley is often attested by the char-
acter of the forest growth ; on the rubble-covered hillsides, where debris
is rapidly removed and therefore always shallow and imperfectly de-
c
Fio. 18.— Diagram showing relative state ot soils in lower part of mountain valley and in the " cove*' at
its head, a, section of lower ]>art of valley; b, section of upper part of valley; e. 0, bed rock. The
relative size of streams is indicated by the section of the beds. The arrows show by their relative
length the proportional speed of the soil movement toward the streams.
cayed, stunted red and black oaks and rigid pines mainly possess the
field, and to the expert eye attest the barrenness of the earth. In the
coves, however, black walnuts of gigantic size, tulip trees with their
great boles, and other plants which grow only in deep and well decayed
deposits of detrital matter show an entire chsinge of soil conditions.
If the land in the valley be cleared of its wood and cultivated we note
an equally sharp contrast in the crops which it bears. On the steeper
slopes, washed at their base by permanent and powerftil streams, the
fields afford only scanty pasturage and generally after a brief trial they
are again abandoned to the natural growth, while in the coves the soil
often proves excellent for the culture of grain, tobacco, or other ex-
hausting crops. The reason for this fertility of the cove soil is to be
found in the ftict that the smaller streams, having near their headwaters
but little cutting power, are unable to convey the detritus away as rap-
idly as in the lower parts of the valley; the d6bris thus has time to be
comminuted by decay and converteil into fertile earth. The difference
between the above-described conditions is diagrammatically indicated
in Fig. 18.
300 ORIGIN AND NATURE OF SOILS.
Withoat discussion it will be evident to the reader that where the
underlying rocks of a district are in the horizontal attitude the soils
will be much more uniformly distributed than they are where the
strata are tossed about by the irregular movements which take place
in the formation of mountain chains. In such disturbed regions the
di£ferent beds often stand at high angles to the horizon, and the distribu-
tion of the debris from them is naturally extremely diversified. Thence
it comes about that in a country of great mountains, such as Switzer-
land, where the x>opulation is dense and the x>eox)le are driven to search
carefully for every bit of tillable soil, small patches of earth of excellent
fertility are often located in districts which are prevailingly unfit for
tillage. Each of these bits of remunerative soil is usually due to the
peculiar nature of the rock which is exi)osed to decay at or near the
place where the fertile field exists. Wherever the beds which afford
these conditions are by the twistings and breakings of the strata sub-
ject to the action of the atmosphere it is likely to give rise to the exist-
ence of similar patches of fertile soil. It often hapi>ens that when the
outcrop of rocks is too steep to permit debris to remain upon its surface
the materials falling to the base of the precipice will gather into a talus ;
there, broken to fine fragments by the violence of their descent, this
rocky matter may aflfbrd the basis of an excellent soil. Many of the
best vineyards and fields of Switzerland and of other mountain coun-
tries are upon slopes of this nature.
Owing to the fact that land in this country is still low priced, but few
of the mountain taluses have been subjected to tillage, and therefore
the peculiarities of soil which are due to the slipping of materials down
the slopes of mountains have not been made the subject of inquiry.
With advancing culture, however, it is certain that we shall have to
imitate the peoples of the Old World and seek every opportunity to
utilize rich lands, however limited in area or difficult of cultivation.
When this stage of our national development arrives thousands of talus
slopes in the Appalachians and the Cordilleras will richly repay care.
Soils of this description are particularly well suited to vineyards. They
serve also very well for orchards and generally for tree plantations of
every description, and this for the reason that the stronger rooted plants,
such as the vines and timber trees, are able to send their underground
branches to great distances through the rubble in their search for an
appropriate food supply.
INHERITANCE.
We have now to consider a peculiar feature in the history of soils de-
rived from rocks upon which they lie, or at least from a place no farther
away than the upper part of the slope on which they rest.. It is evi-
dent that the continued wearing to which soil materials are subjected
leads to a rapid deportation of their mineral materials, either by solu-
tional action or by the direct cutting away by streams. The rate of
SHALESB.! DOWNWEARING OF LAND. 301
this removal of soil can be quite accnrately gauged by estimating the
amount of water discharged from the mouth of a stream which drains a
valley and determining the amount of mineral matter which it contains
for each day in the year. This task has been approximately accom-
plished for all the great rivers of Europe and for the Mississippi in this
country. The rate of the downwearing of the land, according to the
diverse inclination and other conditions of the area, varies from about 1
foot in 800 years in some of the rivers which flow from the Alpine dis-
trict in Europe to about 1 foot in 7,000 years in the Mississippi valley.
Taking the world over, the lands are probably wearing down from the
action of the rain at the rate of about 1 foot in from 3,000 to 5,000
years, the variation in the rate of erosion being due to the amount of
rainfall, the steepness of slox)e, solubility of rock material, and other
influences. The range in the measure of the action is doubtless great;
it probably extends from 1 foot in 500 years to 1 foot in 10,000 years or
more. In some rare instances, as in the very dry and rocky districts of
desert lands, the rate of erosion may be even slower than 1 foot in
20,000 years. Although the subsidence of the surface may seem to the
reader exceedingly slow, as indeed it is when measured in terms of
human history, it is in a geological sense of a moderately rapid nature.
To appreciate the eflfect of this process of lowering the land surface
through the action of ground water and streams in bringing about a
downward migration of the soil we may consider the condition of that
part of the Mississippi valley which has probably been above the level
of the sea for almost all the time which has elapsed since the close of
the Carboniferous period. It is likely that the section of the great
continental valley, which includes the upland country of West Virginia,
Kentucky, and Tennessee, has thus been in the condition of land through
the ages from the end of the Coal-Measure time to the present day.
This great interval can not well be reckoned at less than 10,000,000
years; it is indeed more likely that it represents nearly twice that
duration. Although the rate of erosion in the Mississippi valley, con-
sidered as a whole, is at present not more than sufficient to lower the
surface to the amount of 1 foot in 7,000 years, it seems likely that the
rate of downwear in that portion of the valley which we are now con-
sidering is as rapid as 1 foot in 4,000 years. Assuming that the present
rate of wearing is substantially that which has on the average prevailed
since the region was finally lifted above the sea level, we find that in
10,000,000 years the original soil surface must have been lowered by the
amount of 2,500 feet.
It should be clearly understood that the computation given in the
previous paragraph is intended only to afford a very general idea as to
the probable rate at which the downwearing of the surface of a country
goes on ; the average rate, as assumed, may have been several times
greater or very much less than that indicated. It is not imx)robable
that at various times in the geologic past the speed with which this
302 ORIGIN AND NATURE OF SOILS.
surface has been worn away by the elements has been souietinies far
swifter and again much slower thau it is now.
At first sight it may seem extraordinary and hartlly credible that
such a great amount of rocky matter has gone away from this district;
there are, however, many evidences which point to the concjlusion that
not less than this great thickness of beds has, under the processes of
atmospheric decay, disappeared from this part of the continent. Among
the many considerations which serve to substantiate this conclusion we
may note that the coal fields of the Appalachian were undoubtedly
continuous iicross the table land of central Kentucky where Silurian
strata are now eximsed. This is shown by the fact that the fiinty and
other endui'ing debris of these wasted beds are plentifully intermingled
with the other soil materials which lie on the flat hilltops of this country
in i>ositions where it lias been protected from the assault of the streams.
The total thickness of this destroyed section win not well have been
less than 2,000 feet and may have much exceeded that depth. (See
Fig. 19.)
It need not be supposed that the region we are considering ever had
a surface 2,500 or more feet above the sea level; it is more likely that
d^
h 1^^^- " Mt?<u:^U.*L:i-^^
^^"rT-^TTy , » 7 ' . ' K/. "T ^^ -T-C-L-^ S^
xr rn r
Fia. 19.— Diagram showing the suooessive variations of fertility in the soils of central Kentucky dur-
ing the downward movement of the rocks, a, a, a, parts of tho present surface enriched by decay of
limestones ; ft, next preceding st<age, when soils rested on Devuniaii shales and were moderat4*ly fer-
tile; 6, yet ewrlier stage, when soils were formed on millstone grit and were very loan; <2, earliest
stage when soils rested on the coal measures, and were moilerately fertile. For simplicity of illustra-
tion several stages of variation are omitted.
it has slowly uprisen above the ocean as the beds which covered it have
worn away; but it is necessary to conceive that the soil which we now
find upon its surface has steadftistly moved downward as the beds have
been removed by the action of the agents which wear away land. The
descent of the soil coating has been accomplished by the solvent a<5tioh of
ground water and the cutting work of streams. It is likely that both
these forms of erosion may at one time or another liave operated on all
or nearly all parts of the descending surface. Although at one time
stream beds where the water does its rending work oc(nipy but a small
part of the surface, i>erhaps on an average not over one-sixtieth of the
area, the streams are constantly s>\anging to and fro and so in i)rocess of
down wearing they come to lie in positions far remov<Ml from their present
sites. Only the main divides which separate the waters of considerable
rivers can fairly be supposed to have been exempt from the action of
these migrating channels. (See Fig. 20.)
As soil descends with the wearing away of its materials it of course
is subjected to a constant change in its mineral character. Thus while
soil of the district now occupied by the rich limestone territory of central
Kentucky lay upon the Millstone grit it was doubtless of a sandy and
8RALBB.]
INSOLUBLE MATERIALS OF SOIL.
303
rather sterile nature; wlicu in its descent it came into the limestone bed
it must have been fertile; still fartlier down, encountering the Devonian
or Ohio shale, which, because of its mineral character, is rather unfit for
plants, the soil would again have been reduced to a sterile state. Finally
in downward migration the surface entered the rich fossiliferous beds of
the Silurian age and from the storehouses of the ancient marine life it
acquired the exceedingly nutritious character of the so-called blue-grass
soil; thus with the process of down going the character of the superficial
deposits which determined the fertility of the earth wiis subject to very
great alterations. As forest trees and other plantii are distribut>e(l in
strict accordance with the character of eiirth they grow in, each alteration
in soil brought about in the manner above noted leads to a change in the
species wliich inhabit the area. In tiie field which we have been con-
sidering soils formed of the Millstone grit are occupied by stunted red
M-
"»
**.
. •-" -v
\
•*.
-.a.,-'
., ICL
-?.«^
**
Fio. 20. — Diagram showing tlio lateral miji^ratlou uf atruaniH in thoir descent through inclined rocks, a,
preiient surface; 6, c, former surfaces. The flgiires 1, 2, and .') show the original ]MN»ition8 of the
' streams; 1 a, 1 6, 2a, 2 6, etc., sliowr the successive iNisitious of these streams. The arrows indicate
the direction of the migrations of the st realms.
and black oak and scrubby rigitl pine; where the debris is of limestone
we find walnuts, coffee nuts, and blue ashes, and other trees suited to
the ricli earth. We therefore percinve that ea<5h change in the nature of
soil brings about a revolution in the character of its vegetation. (See
Fig. 20.)
As soil migrates downward the grejiter i)art of the debris which it
inherits from the rock through which it passes is dissolved and goes
away to the sea. There are, however, certain materials wliich may
remain for a long time in tlie soil because they are peculiarly insoluble.
Thus in the limestone soils of Kentucky, the greater part of which are
derived from the rocks on which they now lie, we often find many flinty
and cherty bits which came into the layer when it was in a geological
position a thousand feet or more above the site now occupied by the soil.
Dense jjebbles of pure quartz or flint, containing no admixture of other
more oxidizable materials, may survive the assaults of the elements for
an almost indefinite period. They are indeed almost completely insolu-
ble in soil waters, and when buried in the dense clay they are little
exposed to any agents of decay. It is often possible by tlie silicified
fossils found in this material to prove that it has des(»ended from a
height of several hundred feet above its present position. Other evi-
304 ORIGIN AND NATURE OF SOILS.
dence to the same effect is afforded by the occasional fragments of coal
which are found in certain parts of the country lying upon the Lower
Silurian limestone. One such deposit exists in the southern part of
Campbell County, opposite Cincinnati, where frequent fragments of the
material are found plentifully commingled with the quartz pebbles so
characteristic of the Millstone grit.
It sometimes happens that the barren waste from vanished strata is
inherit'Cd in such quantities upon the present surface of rocks which
yield a fertile detritus that the soil has its fertility more or less impaired.
The rocks which are now supplying newly made mineral waste may
themselves be of an enriching quality, but the plants are embarrassed
by the amount of pebbles through which they have to pass to gain the
nutritious material at a lower level. It will be readily understood that
these conditions are found only where the surface on which the soil
rests is level or lies nearly in that attitude. Where the declivity is
considerable the movement of debris towards streams inevitably leads
to its destruction.
In consequence of the downward migration of the soil the oxides of
iron are sometimes accumulated upon or near the surface in such quan-
tity as to impair its fertility. Particularly in limestone countries these
ores of iron may often be inherited by the surface from beds which orig-
inally lay over the country. It is characteristic of these ores of iron
that they are readily dissolved in the soil water because of the charge
of carbonic dioxide which the fluid contains. Under ordinary circum-
stances in. this state of solution they are in small part appropriated by
the plants, while the remainder is carried away through the streams;
when, however, the soil water containing iron oxide comes in contact
with limestone the iron is deposited in the form of a carbonate, while in
its place the water takes a charge of lime which it bears away to the
sea. In these conditions there may be only iron ore exposed to the
action of the roots of the plants, and thus what would otherwise be a
fertile soil becomes unfit for agriculture. As long as the detritus rests
upon limestone these injurious conditions may i)ersist. If in its down
wearing it passes into clayey or sandy beds the excessive charge of iron
may disappear.
If the soil be excessively humid, as it is in swampy districts, the iron,
whatever be the character of the under soil, may, by virtue of another
chemical process, be retained in the earth. The decomposing vegetable
matter of the morass, by a reaction which it is not necessary to explain,
takes the iron which is contained in the water and deposits it as an
oxide in the form of an incrustation on the decaying leaves and other
vegetable waste lying in the swamp water. As these vegetable forms
crumble in their further decay the iron oxide may be accumulated as a
sheet upon the bottom of the basin. When the downcutting of the
stream which drains the swamp occurs, as it is pretty sure to occur in
a brief geologic time, the ore is left as a deposit on the surface of the
fiHALBR.] ORGANIZATION OF SOILS. 305
soil. These swamp deposits of iron ore are less detrimental to vegeta
tion than those formed in the manner above described, for the reason
that they commonly contain considerable amounts of lime phosphate,
which is a most desirable substance in every soil.
Besides the iron ores, manganese is also inherited in much the same
way from the rocks previously occupied by certain existing soils, but
the oxides of this metal more rarely occur than those of iron, though they
are often associated with them, and the effects of the accumulation are
thus not so disadvantageous to vegetable life.
In general the downward movement of the mineral matter contained
in soils tends to promote their fertility, and this for the reason that the
variety of mineral materials in any one layer of rock is generally insuf-
cient to afford the wide range of substances desirable for the uses of a
varied vegetation. Within each area of ordinary soil we commonly find
a share of the substances derived from the higher levels of the strata
through which it has passed; in this manner it is likely to be supplied
with a wider range of ingredients than the rock on which it lies can afford.
There are also several curious equations of action which tend to prevent
a soil from becoming surcharged with detritus of an insoluble character,
such as flinty pebbles or fragments of chert. When the debris lies on
a slope the constant passage of waste to the neighboring stream clears
the surface of such accumulations; when the area is level the insoluble
materials gradually sterilize the soil so that the vegetable growth be-
comes scanty and the consequent supply of the CO2 to the water so small
that the solvent action of the fluid on the bed rocks is much reduced, and
so the surface migrates downward with lessened speed. With a dimin-
ished rate of descent the hard bits have a better chance to completely
decay, and they are less apt to form a thick coating upon the surface.
On this account we rarely find any soil completely sterilized by the in-
soluble fragments which it contains. Though it may not be fit for ag-
riculture, it can generally, support a scanty forest growth. But for this
partial arrest of the downward working of the surface certain soils
would be so thickly covered with insoluble rock debris that they would
be entirely barren. We thus see that the character of a soil to a cer-
tain extent determines the rate of down wearing of the country, while
conversely the speed of the descent in a measure fixes the nature of
that layer.
The foregoing considerations should give the student a larger con-
<5eption of the historic features of the soil coating than can be acquired
by any more limited view of their conditions. He should clearly see
that this mass of debris, which at first sight seems a mere rude
mingling of unrelated materials, is in truth a well organized part of
nature, which has beautifully varied and adjusted its functions with
the forces which operate upon it. Although it is the realm of media-
tion between the inorganic and the organic kingdom, it is by the
variety of its functions more nearly akin to the vital than to the lifeless
12 GEOL 20
306 ORIGIN AND NATURE OF SOILS.
part of the eartli. It is not unreasonable to compare its ox)erations
to those of the plants which it sustains, for in both there are the har-
monious fonctions which lead matter from its primitive condition to the
higher estate of organic existence.
CERTAIN PECULIAR SOIL CONDITIONS.
So far our attention has been mainly given to the three groups of
soils which are the types of the detrital coating in most parts of the
world, viz, the alluvial, the glacial, and the locally derived dei)osits. In
certain cases, however, we find soils which have been aflected by local
though it may be wide-reaching conditions, and which constitute fields
affording problems of great economic as well as scientific interest.
Among them we shall note the two divisions of arid and inundated lands,
or those which suffer from an insufficient or an excessive water supply,
and also those formed of materials transported through the air, together
with certain other less important types of structure which mil have to
be at least incidentally considered.
It has already been shown that the i^rime mover in the formation of
soils is the water which penetrates into and circulates through the
superficial i)ortion of the under earth ; it is therefore natural that any
great variation in the amount of this fluid should give rise to c<msider-
able differences in the constitution of the mass which it in good part
creates and makes useful to plants. Such, indeed, we find to be tlie case.
When the amount of the underground water and its other conditions
are such that from time to time it fills the soil and then almost altogether
escapes to the streams and air, we have what may be termed the normal
conditions of the layer. Where the water is not supplied in such
quantities as are necessary to these movements, or where the supply is
so excessive that the earth is kept in a soaked state throughout the year,
the effect upon the earth is perturbing and detrimental. Owing to the ir-
regular distribution of the rainfall and in part, especially in the case of
inundated lands, to the slope of the surface, about one- third of the oon-
tineutal areas have an imperfectly ftmctioning soil coating. The arid
lands or those which suffer from insufficient ground wat^r occupy some-
where near three-tenths of the continental area. The swamps or other
inadequately drained lands include about one-thirtieth of the surfa<;e
which is above the level of mean tide.
The arid i)ortiou of the earth is mainly grouped into five great fields,
which lie in central and western Asia, northern Africa, central and
western Australia, western South America, and the Cordilleran district
of North America so far as that field lies in Mexiex) and the United
States. There are other jwrtions of the earth which are desolated by
drought, but they are all of small area. In none of these arid regions
do we find that absolutely no rain falls ; but in them the quantity of tlie
fall is too limited to serve the needs of all save a few kinds of plant^^
which have habits of growth fitting them to live with little moisture.
i
MALEE.] ALKALINE CRUSTS IN ABID DISTRICTS, 307
The amonnt of rainfall in desert countries varies from less than 1 inch
to about 10 inches per annum, and in most cases the supply comes to
the earth in some one season, sometimes in a single brief rainfall. Wlien
the rain is precipitated in this fashion, even as much as 20 inches falling
in a season of 1 or 2 months, though it may nourish certain forms of
plants adapted for development in the short time during which the soil is
moistened, the region may be classed as arid, for it will be unable to
maintain our ordinary forests and except when artificially irrigated will
be generally unfit for tillage.
Arid soils commonly exhibit certain peculiarities which are not found
in those of ordinary humidity; they are usually of more than average
depth, for the reason that while the amount of water may be quite suf-
ficient to promote the chemical decay of bed rocks, there is not sufficient
passage of the fluid through the debris to bring about much deportation
of the material in the state of suspension or solution. Even where the
mass of debris is tolerably deep and open in its structure continued
droughts preceding the time of ra|n and the general absence of a layer of
vegetable mold commonly cause the soil to present a dense baked sur-
face which may shed the rain like a roof. So, too, the lack of any but
ephemeral vegetation, or of stunted plants which ftimish little organic
debris, diminishes the amount of mold which is contained in the de-
tritus, so that the mineral elements of the soil are insufficiently mingled
with organic matter. Held below the compact surface and with no
great amount of transfer of the soluble mineral matter to streams, the
soils of this arid nature in time become superabundantly charged with
the various saline matters which are of much imjwrtance to organic life.
Although the process by which these substances are brought into a
soluble form goes on more slowly than in the case of ordinary soil, be-
cause their removal is not brought about, they slowly accumulate until
they become in quantity far greater than in ordinarily humid parts of
the earth.
When the potash, soda, and other soluble materials stored in the arid
soils become excessive there is a curious action manifested by which
they are uplifted to the surface and form a coating upon it. This coat-
ing may appear as a thick and enduring crust, such as occurs in certain
parts of the well known alkaline plains of the arid region of the Cordil-
leras. The process by which these saline materials are brought to the
surface is as follows : When in the season of brief rains the soil becomes
for a time tolerably wet a large part of the alkaline matter is taken into
solution in the ground water. The dry air evaporates a portion of the
fluid next the surface, and this, passing into the form of vapor, leaves
its mineral contents at the place where it went into the atmosphere. As
the interstices of the soil are left empty by the disapx)earance of water,
some of the fluid from below rises to the surface and in turn goes through
the same process. In arid as in other soils the spaces between the grains
act in the manner of those in a lamp wick to draw up the lower fluid to
308 ORIGIN AND NATURE OF SOILS.
the point where it escapes by the action of heat in the form of vapor:
as in the lamp the solid material contained in the oil forms a crust at
its top, so the mineral matter of the soil water incrusts the surface of the
earth.
In the manner described in the preceding x>aragraph, the alkaline
materials of arid soils in times of drought migrate to the surface; if the
rainfall be suflSciently heavy, it may in the next wet season dissolve the
crust and return the material to a lower part of the soil ; if the rainfall
be lass in quantity, it may happen that for at least a term of years the
crust will remain on the surface of the soil. The effect of this excess of
soluble material is gradually to add to the sterility of the earth in which
it occurs; but this influence is frequently transitory j it endures but for
a short time after the soil is by art provided with sufficient water to
wash away an excess of soluble materials. These alkaline districts are
in most cases admirably suited for betterment by irrigation; it requires
but a thorough washing out of the excess of saline matter, such as can
by irrigation be quickly brought about, to convert such a district into
fertile ground. In general these earths which contain an excessive
amount of soluble material lie in the more level i)ortions of the country;
where the soil is upon steep slopes, the effect of gravity, acting ui>on the
surface water as well as that which penetrates the ground, is to urge the
fluid more rapidly down the slope and thus to secure the deportation of
the alkaline matter; consequently the more steeply lying land of the
district may be exempt from alkaline crust, while the flat country may
be covered with the coating.
It is a noteworthy fact that in the region of the great basin of the
CordiUeras the valley deposits are coarse and pervious to water in their
margins near the bases of cliffs, but fine and impervious in the centers
of the several basins whereunto only the flner portions of the detritus
worn from the mountains has been conveyed by the action of water and
air (see PI. xiv).
In many parts of the United States the ordinary brick used in ma-
sonry, after being built into a wall, frequently exhibits an alkaline
crust, the formation of which is exactly comparable to that found in the
arid plains of the CordiUeran district. When a wall composed of these
brick becomes soaked by a beating rain various soluble substances are
dissolved by the water which has penetrated the masonry. During dry
weather this water evaporates on the surface of the wall substantially
as it does on the surface of the soil, and a similar coating is formed.
Unless x)ains be taken to scrape away this facing crust the greater
part of the matter will be returned to the brick during the next spell of
rainy weather, and so sometimes for 20 years or more the alkaline mat-
ter will perform a succession of journeys into and out of the baked clay.
It must not be supposed that tbe formation of this alkaline coating is
altogether i)eculiar to arid districts, though its results are most evident
in those fields. The same action takes place on all soils whatsoever in
8HALBB.] FORMER CONDITION OF ARID LANDS. 309
the change from wet weather to dry. Even in regions of ordinary rain-
fall where the earth is fairly rich in soluble salts the attentive eye will
detect the beginning of such a coating. It is the frequency of rainfalls
which prevents the sheet from becoming a distinct feature. It is per-
haps worth while to note the fact, though it has been before adverted to,
that it is to this constant elevation of the plant food nearly to the top
of the soil which enables our grain-bearing plants to find sustenance in
large quantity near the surface.
In certain rai'e cases the process of watering arid land, if a sufficient
exit for the fluid is not provided, leads to the formation of an alkaline
crust; thus in the delta of the Nile, where the quantity of water avail-
able for irrigation is scanty and the price set upon it high, people have
endeavored to economize by providirg insufficient exit for irrigated
land. In this case the alkaline materials derived from the deeper por-
tions of the soil form a coating on the surface during the long dry
season, and the vegetation suffers from an excessive amount of mineral
matter in the soil, which is in a state to be taken into solution. When
these alluvial deposits were formed they contained no excess of soluble
material, but lying for ages in the deposits they have become more
decayed and thus a relatively large part of the mineral matter enters
into the soluble state; it is evident that tliis affords au excellent exam-
ple of the progressive decay of detrital materials deposited in the river
plain.
Much of the exceeding fertility which characterizes the lauds of the
arid district when they are properly irrigated is doubtless to be accounted
for by the i)eculiarities of climate of the region in which these fields lie.
In such a district the sky is prevailingly cloudless and the measure of
sunlight which comes to the surface is much greater than in humid
regions. The result is that if their roots be well supplied with water,
many plauts flourish in the dry air with much greater luxuriance than
where the moisture comes to them altogether from the rain which falls
on their leaves or on the ground about them.
In most cases the soils which are now arid have not been in that state
for any considerable geologic time. Their present condition is due to
climatic changes which api>ear to have come about with the decline of
the glacial i)eriod. This alteration is most conspicuous in the Cordil-
leran region of North America. It is also evident on the arid western coast
of South America. It is especially marked in the district of the Rocky
Mountains, in northern Mexico and the United States, where we find the
surface dotted over with old lake-beds the waters of which once cbvered
a large part of the area, making the country one of the most extended
and beautiful lacustrine fields in the world. Many large lakes, like that
in its shrunken form known as Utah or Salt Lake, occupied extended
plains and valleys which now contain only the diminishe<l remnants of
those seas. In place of fresh water these lakes now present alkaline or
salt pools of trifling extent. When these inland seas were full of fresh
310 ORIGIN AND NATURE OF SOILS.
water there must have been a relatively great rainfall in this region now
arid. The valleys which at present are the seat of streams only during
the brief rainy season were then occupied by large and i)ermanent
rivers, so the soil generally must have been the seat of luxuriant for-
ests. The result of these variations is that the existing detrital dei)08it8
of that region are in part at least derived from a time when soil-producing
agents were more active than at present. It seems very doubtful if
the existing soils of this area could have been formed in the conditions
which now prevail.
The insufficiently leached soils of the arid region shade off indistinctly
into the better watered soils which surround them. Sometimes, indeed,
where the region is far too arid to i)ermit the growth of forests or the
use of the land for tillage, but where it is of an open texture, the rainy
season being characterized by a brief but abundant downfall of water,
the leaching x)rocess, though limited in duration to about a month, is
sufficient to prevent the soil from retaining an excess of alkaline mate-
rial. Whatever be the precise nature of these arid soils, and they are
almost as varied in their qualities as those of normal humidity, they
commonly prove of unusual fertility when redeemed by a proper system
of irrigation. This fertility is due to the fact that they have not had
their soluble material freely transi)orted to the sea by the excurrent
ground water. Moreover, a large part of their mineral constituents are
in a decayed state, and thus readily pass into a condition fit for plant
food as soon as the mass is supplied with water and intermingled with
the waste of decajing vegetation.
Passing from the arid soils to those which are excessively humid, we
traverse a wide gradation in the conditions of these detrital deposite
as regards the amount of their water supply. The range is very great
in the quantity of rain which faUs upon the surface of soils classed as
neither arid nor inundated; it may be taken as varying from 15 to 600
inches per annum. This difference has no such effect as would at first
sight seem likely to ensue, for the reason that whatever the amount of
water which falls uiK)n the surface the excessive supply has no effect
upon the deposit, after the interstices of the soil are filled, save to swell
the streams and thus increase their carrying power. The soil takes in
rain water up to a certain x)oint, which is determined by the sjieed at
which the fluid can drain from the detritus into the streams; any ad-
ditional amount is surplusage and has no influence on the under earth.
On the other hand, when the quantity of water in the soil is less than
is required for the maintenance of its functions, unless, indeed, it has
become baked by enduring drought, the pores of the earth greedily
drink in not only the rain but even the dew which falls each night.
This provision for the dew is generally disregarded in the account taken
of the water supply of a country; yet it is often of as great value as
the rainfall, and sometimes maintains a moderate fertility in a land
which would otherwise be sterilized by drought. During the time when
8HALKB.1 SOILS OF SWAMP DISTRICTS. 311
the dew is falling and lies ui)on the ground and the foliage, a period
that commonly lasts for about half the day, evaporation from the earth
and from the leaves of plants is arrested. Moreover, many of the lesser
plants have their leaves and stems so arranged that their expanded
surfaces gather the water and lead it down to the roots, and thus
moisten the earth in the most advantageous manner.
When during any period of drought in the upi^er part of the soil,
however dry, the capillary or wick-like action of the spaces between its
grains causes the water to rise from the lower levels to the field occupied
by the roots. Herein lies one of the advantages of securing a deep soil
by proper methods of tillage; the water can be stored in the interstices
of the lower levels, and when demanded can be brought to the upper
levels where the roots can obtain iiccess to it. Forest trees can i)ene-
trate the under soil and seek out the stores of water in the lower earth,
sometimes to the depth of 10 feet or more; but more delicate annual
plants, which afford the greater part of our crops, can not in their brief
period of growth push their roots more than 6 or 12 inches below their
crowns.
SWAMP SOILS.
As long as the measure of humidity is such that a soil may occasion-
ally become moderately dry, so that the air can penetrate into the inter-
stices, it may be regarded as still in the class of normal deposits of this
nature, wherein the supply of water is such that the alternate wetting
and drying can not take place, but the interspaces being continually
filled it enters into the group of swamp soils. In this class of deposits
the exclusion of air makes the matter unfit for the needs of most plants;
their roots can not secure the aeration which they demand; in fact,
there are only a few rather singular species which can make their roots
serve them in a soil which is continually filled with water during the
growing season.
Swamp lands exhibit considerable diversity as regards the origin and
nature of the deposits which constitute their soils; in all cases, however,
they are characterized by a greater proportion of organic matter on their
surface, or in their upper part, than is found in ordinary soils. This is
due to the fact that when animal or vegetable matter is immersed in
water it decays moi*e slowly than when it is in succession wetted and
dried. Woody substances when submerged in water gradually pass into
the state of peat or muck, and beyond that stage of decay change goes
on verj^ slowly or is entirely arrested. The normal result is that in
these inundated areas there is an ever thickening deposit of half-decayed
plant waste, which generally contains not more than from 5 to 10 per cent
of mineral matter — ^far too little, indeed, to give it the qualities of a good
soil. Although the roots of certain plants find their needed sustenance
in these swamp accumulations they are essentially unfit for the growth
of the ordinary forest trees, and for nearly all the tillage plants until
312 ORIGIN AND NATURE OF SOILS.
they have been drained and subjected to an exposure of the air for a
considerable period. When unwatered and allowed to undergo a suffi-
cient decomposition from the action of the atmosphere they invariably
prove to be of great fertility, and endure the tax of culture remarkably
well. A large part of the best lands in Euroi)e have been won to tillage
from ancient morasses. In this country the area of such lands which
are suited to improvement by means similar to those which have been
successftdly adopted in the old world exceed 100,000 square miles. In
general lands of this class constitute a most important reserve, from
which extremely fertile fields may in time be obtained, capable in the
B'ggregate of supplying food for a population nearly as great as that
now contained in this country. It is therefore worth our while to glance
at the history of these morasses, noting the diverse conditions under
which they are formed and the effect of these on their possibilities of
reclamation. A more detailed explanation will be found in the general
account of inundated lands in the Tenth Report of the Director of the
U. S. Geological Survey.
The simplest class of swamp deposits is formed where a thick forest
growth, in a region of no great excess of rainfalls and of approximately
level surface, leads to the retention of water in the soil to an injurious
degree. In such an area the dead leaves and branches encumbering
the ground so delay the passage of water to the streams that the clear-
ance is not effected from one rainy i)eriod to another. In this case the
plants, particularly mosses, reeds, and rushes, possess the ground;
species of trees originally inhabiting the district are generally expelled,
and the field remains deforested or is occupied by those varieties only
which can live amid the hostile conditions. In many parts of the world
this action leads to the deforesting of extensive tracts of tree-covered
ground, a sheet of bog earth taking the place of the original growth.
In earlier states of this process the pioneer may easily convert the
ground into tillable earth by clearing away the forest and breaking up
the thin sheet of swampy matter with the plow. When the deposit has
so far thickened as to drive the forest trees away, however, the layer of
spongy matter is generally too deep for immediate tillage, and the field
must be improved by ditching. This class of wet woods is less common
in the United States than in the region to the north ; yet such areas,
often of great extent, are common in the part of the country east of the
Mississippi and north of the Ohio and the James rivers, and are of oc-
casional occurrence in more southern and western fields. Morasses of
this sort are most apt to occur in cold climates where the snowfall is
great in quantity and where the summer is moist. Under these condi-
tions the ground has not time to dry during the short summer season.
They are particularly likely to be found where the area has newly been
elevated above the level of the sea and has the characteristic nearly flat
surface proper to ocean floors. Whenever the surface slopes toward
the streams with a descent of less than 5 feet to the mile, unless it is
I
il
is
8HALBB.] SOILS OF FLUVIATILE SWAMPS. 313
underlaid by very coarse porous soil, it is likely to take on this upland
swamp character. The great dismal swamp of Virginia and North
Carolina lies on a fine sandy soil with a slope of about 20 inches to the
mile, yet it is covered by a thick layer of peaty matter (see Pis. xxvn,
XXVIII and xxix).
Next after the sloping upland group of swamps we may note those
inundated lands which lie on the alluvial plains of our greater rivers.
These are due to the frequency or persistency of floods which rise above
the channel of the river. They are usually most extensive and difficult
to win to the uses of culture along the lower banks of a river where its
waters are checked by the nearness of the sea, and the height of the
plains is lessened by the fact that the slowing current has allowed all
but the finer sediments to lodge in the upper parts of the valley. As is
well known, these fluviatile plains are almost always highest nearest
the margin of the river, and they slope thence toward the hills which
bound the valley in the manner indicated in Fig. 14. Although the
elevated border of the terrace may have sufficient height above the
river to furnish the drainage necessary for a normal soil, the lower lying
back country is usually so depressed as to have a swampy nature.
The waters from these "back swamps" are with difficulty discharged,
for any small stream which may cut through the elevated strip next the
river is likely to be from time to time closed by the sediments of the
main stream or blocked by driftwood which readily enters the passage
which its mouth forms through the aUuvial plain. Generally the drain-
age of these swamps is effected by a gentle drift of waters parallel to
the river which goes on until the volume is great enough to secure a
permanent exit to the main stream. As this current is checked by the
mass of living and dead vegetation through which it passes it often
comes about that these back swamps are maintained when there would
be dry land in case the path for the escape of their waters was free (see
PL XXIX).
The fluviatile swamps include another class of morasses formed when
the stream abandons a portion of its channel seeking a shorter way to
the sea. These swamps do not differ from those formed in lakes and
will be considered under the head of lacustrine deposits. It is charac-
teristic of the back-swamp deposits of the river plain, as in general of
all of this class of sediments, that they commingle organic and inorganic
matter in a very i)erfect way. Thus these fluviatile swamps contain a
much larger proportion of inorganic sediments than the commoner class
of morassal deposits formed in lake bai^ins. The result is that these
soils when drained are in almost all cases at once fit for tillage without
the time-consuming and costly process of removing the excess of vege-
table mold. When adequately drained they can usually be made serv-
iceable to the farmer at once. The greater part of the delta of the
Mississippi is occupied by morasses of this nature. The fertile lands
at the mouth of the Ehine are also to a great extent winnings from the
same class of inundated soils.
314 ORIGIN AND NATURE OF SOILS.
The last group of fresh- water morasses which needs be mentioned in
this paper is that which owes its character to the lacustrine conditions
of its deposits. Whenever a water basin is formed without distinct
current movement, a number of aquatic sx)ecies of plants diftering in
various parts of the world, but all fitted for growth in very humid soils,
seize upon the earth at the margin of the basin and proceed to accumu-
late a layer of vegetable mold upon and beneath the surface of the
water. If the level of the lake be variable in a considerable degree, or
if from its size and form of shore all parts of the coast line be subjected
to strong waves, these plants may not succeed in beginning the work
of filling in the basin with vegetable matter; but it commonly happens
that in the shallowed parts of the shores the mosses of the genus
Sphagnum and some few floweiing plants find a foothold and create a
layer of living and dead roots, leaves and stems, forming a tough peat.
This deposit, though it begins to grow on the shore, gradually extends
out over the surface of the water on which it floats. As it grows on the
top it settles down into the lake and finally comes to rest upon the bot-
tom. While this top sheet is fomung and extending its margins by
continued growth in its upper parts, it is decaying in its under portion and
Fio. 21. — Section across ordinary lake in glacial drijft. a, bed rock ; b b, drift ; e e, growing iieat float.
ing in water ; d d, decayed peat on bottom ; e e, climbing bog.
the fine carbonaceous mud is settling to the bottom. When the process
is finished the lake is closed with the peaty accumulation. Only the
larger areas of water, which have at the same time more considerable
depth and thus by their powerful waves break up the advancing sheet
of organic growth, can keep their basins open, however wide they may
be, for their bottoms are shallow, the growth of reeds, rushes, or lilies
is likely to form a natural breakwater in front of the peaty layer which
serves to fend their assault from the spongy advancing shelf. In this
manner at least nine-tenths of the very numerous lakelets which existed
in the northern part of the continent at the close of the glacial period
have been closed with organic waste. (See Fig. 21.)
Unlike the peat which forms in the swamps of alluvial terraces, that
of the lacustrine swamps generally contain but little mineral matter.
It is indeed so devoid of it that it can not be used for tillage until the
ground is not only drained but the peaty layer burned away or allowed
to decay in the slower manner in which atmosjiheric aetion effects this
end. Deposits of this nature are often so deep that the task of remov-
ing the vegetable matter is practicably imix)ssible of execution. In this
case the only way in which these areas can be made of profit is by using
them as nurseries of certain species of trees, to which they are often
I
8HALKB.J PH08PHATIC DEPOSITS IN SWAMPS. 315
well adapted. The juniper and the bald cypress, the tupelo, the water
maples and the willows and the birches, a« well as a number of other
useful timber trees, have developed a certain endurance to the excessive
humidity of swamps. In certain ca^es, as in that of the tupelo and the
bald cypress, the tree has developed a peculiar form of roots which
causes the aeratiou of sap in such a manner that it can withstand an
amount of moisture sufficient to destroy many other species. It is
probable that the greater part of our lacustrine swamps will in time be
made to serve as nurseries of timber.
Another form of agriculture in which these peat swamps can be made
of use is indicated in the method in which cranberries are extensively
reared in Massachusetts, and elsewhere along the coast as far to the
south as southern New Jersey. This form of tillage is perhaps the
most original of any which has been invented in this country. In pre-
paring swamps for this mode of culture, the top part of the original bog,
that containing all the living roots and stems, is cut away, and the
lifeless muck which lies below the removed layer is covered with a layer
of sand several inches in depth, which is evenly spread over its sur-
face. In this layer of sand the plants are rooted, and through it may
descend to the underlying vegetable matter. The advantage of the
sandy layer consists in the fact that the weeds do not readily root in it;
moreover, it affords a firm footing to the laborer. It is likely that this
method of tillage may advantageously be followed in the case of other
economic garden plants, which, while they require dry ground for their
crowns, luxuriate in a soil abounding in vegetable matter.
The soil bed of modem fresh-water swamps, the layer which lies be-
neath the accumulation of peaty matter, is commonly not of a fertile
nature. This is owing to the fact that the movement of water which
takes place through it is generally slight; little air penetrates into the
interstices, and so the decay of its stony material goes on slowly ; there is
none of that constant overturning of materials, which, as we have seen,
takes plaee in ordinary soils, such as those on our uplands. The deposit
formed on the bottom of our swamps does not constantly descend by
the process of mechanical and chemical erosion through the strata on
which it lies, and thus there is no renewal of the fertility of the bed
due to this action. Influences, however, are at work which bring about
the formation, just above the bottom of the swamp, of a deposit of
greater or less thickness which commonly contains a considerable
amount of lime phosphate, a substance of great value in the produc-
tion of most economic crops. The mode in which this accumulation is
formed is not yet well understood, but it seems to be in general as fol-
lows:
In the water of most modern swamps as well as stagnant pools there
commonly dwell a great variety of smaU crustaceans which have the
habit of appropriating the phosphatic matter from the animals and
plants on which they feed. This material they deposit in the outer coat
316 ORIGIN AND NATURE OF SOILS.
of their body, or, as it is commonly called, the ''shell." When these
creatures die, their remains are doubtless in part dissolved and reap-
propriated by other organic forms, but in part they find their way
to the bottom, and there along with other mineral materials form a layer
rich in fertilizing matter. If the water which enters a morass is
charged with iron, this layer generally appears as a bog ore; but in most
swamps the amount of the oxides of thfs metal is so small that the deposit
is not of that nature, and the phosphatic material is thus the more ready
to serve the needs of the plants which call for it. The solubility of
lime phosphate is much less than that of other comiK)unds of lime, so
that it is not borne away in solution as readily as ordinary limestone
would be; in consequence of this limited solubility the bottoms of the
swamps often come to contain a remarkable amount of grain-producing
material. (See Fig. 22.)
The phosphatic matter which finds its way into swamps and is there
stored in the deiK)8its accumulated on their bottoms is doubtless in all
cases derived from the rocks lying in the region whence the streams
Fio. 22.~Diagramatic section throufifh lake kaaiu showing fonuatfon of iufUsorial earth, a, bed rock;
b b, floating peat ; e e, decayed peat; d, infusorial earth.
which flow into the morass drain. Almost all strata except the purer
sandstones and flinty rocks contain a notable quantity of this substance,
which was built into their masses at the time when they were accumu-
lated on the ancient sea floors, the material coming to it« position in the
bodies of fossil animals and plants, which in turn obtained it from the
sea water. Entering the swamp through the rivers the lime phosphate
is first appropriated by certain water plants; these are eaten by fishes
and crustaceans, and when these animals die their skeletons convey the
phosphatic material to the floor of the bog, where it is slowly built into
a layer.
It is through the local accumulation of phosphatic matter in some-
thing like the manner above described that the swamp soils accumu-
lated on the sand of eastern Virginia and North Carolina have been
made exceedingly fertile. In that region, through the enrichment which
the organic forms of the swamp waters have contributed to the dei)osit
on the bottoms of the morasses, the drained ground affords extremely
fertile fields. Thus, while the sandy region about the Dismal Swamp
is essentially worthless for grain crops, the dewatered swamp land yields
even to a rude tillage exceedingly large returns. These fields often
afford rich harvests for many successive years without any fertilizing
whatever. (See Fig. 23.)
BHALEii.] MABINE MARSHES. 317
The swamp lands of the United States, which are the most redeem-
able and which when won to the uses of agriculture aflford fertile
fields, lie mainly on that i)ortion of the Atlantic sloi)e between New
York City and the mouth of the Mississippi River. Almost with-
out exception these morasses lie at sucli height above the sea that by
the use of simple engineering contrivances they may be effectively de-
watered. In general these fresh-water swamps are covered with a dense
growth of timber, which, owing to the fertility of the soil, is inter-
mingled with a very thick growth of underwood, climbing vines, reeds,
and other water-loving plants, so that the cost of clearing away the
luxuriant vegetation must be added to the considerable expense which
is afterwards required in draining the land by ditches. Nevertheless
the quality of the soil is so good and its endurance under cultivation so
continuous that the next great step in the economic development of the
eastern iwrtion of the United States will i)robably consist in the redemp-
tion of these inundated lands. In the general accounts of the swamp
districts of the United States contained in a memoir published in the
Flu. 23.— Dia^n'tunatic sectiou troni seashore to interior of district recently elevated above tlie sea level.
a a, bed rocks; b, beach deposits and dunes; e e, marine sands with gently rolling surface.
Sixth Annual Report of the Director I have given a somewhat special
account of these redeemable swamp lands. It may be here noted that
some of the largest fields for the enteri)rise of the engineer lies in the
State of Florida, where there exists about 28,000 square miles of country
more or less adapted to such improvement.
Although, as before remarked, the larger part of these coastal swamps
of the United States are covered by dense forests, certain fields which
are destitute of arboreal growth invite improvement. Thus a large
part of the Everglades in southern Florida is open land, but is almost
covered by a growth of reeds and other relatively slight vegetation.
There are also considerable areas, generally lying in tlie central portion
ot timbered swamps, which are so far covered with water that they appear
as tolerably permanent lakes, such as Lake Drummond, of the Dismal
Swamp, of Virginia. In most regions these lacustrine areas will, when
drained, afford fertile ground, but in some instances their bottoms have
not received a coating of vegetation and remain as bare sands, scarcely
more fitted for the uses of agriculture, even when thoroughly drained,
than the general surface of the plains which lie without the limits of
the morass.
MARINE MARSHES.
The last class of humid soils which we have to notice is that which
includes the viiried fonns of tidal marshes which are formed along the
318 ORIGIN AND NATURE OF SOILS.
seashore. These marine moranseH are produced wherever there is a
tidal movement of more than 1 or 2 feet in altitude. They accumulate
in the indentations of the shore which are sheltered from the action of
the greater waves, for the reason that in more exx)osed places these
surges break up and scatter the frail accumulations as rapidly as they
are fonued. Like the lacustrine swamps, marine marshes begin with the
growth of a fringe of vegetation next the shore; but while the mosses
play the principal part in forming the peat dei)osits of fresh water, the
grasses, certain species of which have the capacity of enduring salt
water, do the work of constructing these marine deposits. The shelf
they build is at such a height that its upper level falls just below the
plane of high tide, so that with each oscillation of the waters a depth
of a few inches is for an hour or two laid over the surface of the marsh.
Each recurring tide not only refreshes the plants but it also brings in
among them more or less floating debris, which catches in the tangle
of the stems and gradually adds to the mass of the deiK)sit. Beginning
to grow, with water of considerable depth, the shelf in this manner grad-
ually attains to near the level of high tide. This sheet of dense fibrous
peat, composed mainly of plant remains, is mingled not only with the
materials washed in by the tide, but is in part comx)08ed of the waste
Fig. 24.— Diagrammatic section showing the origin and general structure of marine marshes, a, original
surface at shore line; b, grassy marsh; e, mud flats; d, eel grass; e, mud accumulated in eel grass
growth.
derived from the numerous small animals, such as shellfish and crus-
taceans, which dwell in tlie interstices between the plants. Unlike the
lake swamps, this sheet of organic matter, formed as above described,
never floats on the water; it lies upon the bottom and firmly adheres
thereto. At the margin of this sheet of vegetation the waves from
time to time break up the structure of the mass and distribute the waste
over the bottom of deeper water, thus shallowing it and making it easier
for the organic shelf to advance farther into the bay (see Fig. 24).
The construction of this tidal peat is still ftirther favored by the growth
of the interesting plant commonly known as the eel grass (Zostera mari-
tima) a species of true flowering plants that has acquired the habit of
living with nearly all parts of its body permanently below the level of
water. Even a portion of its flowers are permanently covered by the
sea. Growing in a densely crowded manner, this singular plant, by its
remains and by the quantity of detritus which it gathers in its entangled
foliage, shallows the areas of the bays in which it grows and so makes
6HALKB.] FERTILITY OF MARINE MARSHES. 319
a foothold over which the higher lying turf gradually extends. Favored
by these conditions, the tidal marshes gradually spread over the shoals
of our bays, finally closing all the sheltered inlets of the coast except
where the depth and wfdth of the indentations is such as to x>ermit the
waves to beat against their shores with great violence. Thus along
the coast between New York City and Portland, Maine, the growth of
these x)eculiar marine marshes has diminished by more than one-half
the area of the harbors which were occupied by tolerably deep water at
the close of the last glacial period. The total area of these accumula-
tions which are now bared at half tide along the part of the shore above
referred to exceeds 350,000 acres.
Along the shore-line between New York and St. Augustine, Florida,
these tidal marshes are very extensive and widely distributed; they
contain an area many times as great as that presented by the shore of
New England. The total surface which they occupy has not yet been
well ascertained, but it probably amounts to some thousands of square
miles. It is a noticeable fact, however, that the character of these
marine marshes gradually alters as we go southward; with the change
of species of the plants which compose them and the alteration in the
energy of tidal currents due to the diminished height of oscillation they
exhibit a marked change in their character, the plants grow less thickly,
and the deposits often assume the character of muddy flats. South of
St. Augustine and around the shore-line of Florida these marine marshes
are generally covered with a growth of mangroves, a tree of curious
structure and habits which by its peculiarities is able to grow in salt
water. It is probable that within the limits of the United States the
total area of marine marshes, including only the deposits which are
bared at half tide and which owe their formation mainly to the growth
of grass-like plants, is nearly 10,000 square miles.
The quality of the soil which may be won from these organic accumu-
lations of the shore land is excellent. Owing to the abundant remains
of animals, they are remarkably rich in those materials which are most
necessary for vegetation and which are rarest in ordinary upland soil;
lime, potash, soda, and phosphate are commonly present in relatively
large quantities; in fact, these marine marshes in their excess of soluble
materials in many ways resemble those which are found in arid districts.
In both cases the excess of such matter is mainly due to the imperfect
circulation of water through the soil; in the case of the arid land from
the lack of water; in that of the marine marshes, from the fact that the
fluid does not, during the brief time when the mass is exposed to the
air, have a chance to discharge the water it contains.
When these marine marsh lands are won from the sea they afford
soils of remarkable fertility and endurance to the tax of culture. It
requires, however, a certain time after the surface has been barred from
the sea before the soil of the marsh is fit for tillage; the tough layer of
fibrous roots must first be destroyed by decay or by fire and the excess
320 OBIGIN AND NATURE OF SOILS.
of saline materials removed by solution in rain water before the earth is
adapted to the growth of plants which yield valuable crops. These
changes will spontaneously take place in the course of from 3 to 5 years
after the sea is excluded from the marsh, but by breaking up the sur-
face with a plow and cutting frequent ditches through the plane a single
year will often suffice to bring the soD into the state where any of our
domesticated plants will grow upon it. At first, in just the manner
of the arid fields of the desert region, and for the same reason, this
marme marsh soil will in times of drought form a crust of salme mate-
rials on the surface. As the drainage becomes more complete this crust
ceases to appear, as it does on the alkaline plain after a thorough irriga-
tion. As the excess of organic matter decays the surfaceof the reclaimed
marsh settles down until it comes to rest at a x)oint of from a foot to
18 inches below its original level.
Some of the richest fields of this country are yet to be won from these
salt marshes of the ocean shore. So far but little has been done to
reclaim them. A few small areas in Massachusetts, New Jersey, and
Delaware, probably not amounting in the aggregate to more than 5,000
acres, have been diked from the sea and reduced to subjugation more
or less complete. Of these reclaimed areas the largest lies in Marshfield,
Massachusetts. Here a district of about 1,500 acres has been separated
from the ocean by means of a small dike. There are many other places
along the shore between New York City and Portland, Maine, where
areas of from 50 acres to 16,000 acres can, in a similar way, be reclaimed
at a relatively small expense. By the use of proper machinery the cost
of diking, ditching, and breaking up this class of soils will probably not
on the average exceed $100 per acre. Considering the exceeding fertil-
ity of fields thus won from the sea and their remarkable endurance to
agriculture, which permits them to be cropped for a generation without
the use of fertilizing materials, they may fairly be regarded as remuner-
ative investments even at this considerable cost of preparation. The
experience of the seaboard states of northern Europe clearly shows
that these marine marshes aflford a most valuable resource for the ftiture
of American agriculture.
TULE LANDS.
Among the many local varieties of soil which have attracted attention
and received special names we may note one of the most interesting
varieties, known in California as tule lands. These deposits are to be
ranked in the group of swamps. They mostly occur in the valleys of
the San Joaquin and Sacramento and especially in the lower portion
thereof. They consist of very extensive marshy districts which are sub-
jected to inundations and which occupy in general the position of allu-
vial x)lains in other parts of the country. Near the level of the sea these
marshes are mostly occupied by species of the round rushes; at higher
points in the valleys is a greater variety of grass and rush-like vegetStion.
8HALKB.] SOILS OF FORMER GEOLOGICAL AGES. 321
It has been found tlmt when these lands are subjugated by drainage
or by burning the peaty matter in the dry season the ground is admi-
rably adapted to grain crops. Even without plowing, after treatment
by fire, the ashy soil yields remarkable returns of wheat.
It seems likely that the relatively very great fertility of these tule
lands as compared with the reclaimed swamps of the eastern part of the
United States may be explained by the comparative dryness of the
country in which they are found. There are many reasons for believing
that the climate of the California district is prevailingly drier at the
present time than it was in the immediate geological past. It seems,
therefore, likely that, although at many places still quite wet, these
swamps have somewhat dried away; a good deal of their vegetable
matter has decayed and the ashy waste thereof is commingled with the
peat which remains, adding much to its fertility. Moreover, the quantity
of dust transported through the air in this part of the country is great,
and in the course of time the contribution of enriching sediment from
this source has probably been considerable.
There appears to be more variation in the character of these tule lands
than in swamp deixisits in other parts of the country. Thus it has been
noted that those which lie near Tulare Lake afford a heavier soil than
similar deposits found elsewhere in California. A detailed discussion
of these variations here would be out of place; moreover, the present
writer has not had the opportunity personally to observe them.
ANCIENT SOILS.
Although the soil-coating of the earth is in a certain way an ephem-
eral structure and is commonly subjected to immediate destruction
where it is affected by the action of the waves, by glacial wearing, or by
other violent accidents, some parts of this detrital coating in certain
times and places have by chance been preserved to us from a remote
geologic past. The first clearly recognizable deposits of this nature are
found in the rocks of the Carboniferous age, where, indeed, they plenti-
fully occur; beneath each bed of coal we commonly discover a layer of
material which was the soil in which began to grow the plants from
whose remains the coal bed was formed. So as far as these coal-pro-
ducing plants were rooted forms they generally drew their sustenance
from these ancient soils. We can still in many instances trace their roots,
and occasionally we find the tree fern or other plant to which they belong
standing erect amid the swamp deposits which accumulated about it, and
which now appears a« coal. These soils of the Coal Measures differ from
those now existing on the upland parts of the earth in certain important
ways; they are generally of less thickness than are those of to-day
which have been formed under similar conditions, and contain a rather
smaller proportion of organic matter. These peculiarities are probably
due to the fact that in the olden time there were few kinds of plants
12 GEOL ^21
322 ORIGIN AND NATUBE OF SOILS.
which had strong roots, and thus there was less opportnnity for vege-
table matter to become commingle*! with the earth (see Fig. 25).
The most peculiar feature of these
ancient soils consists in the fact
that they usually lack those mate-
rials, such as jiotash and soda, which
are a conspicuous and necesstu-y ele-
ment in the greater part of the soils
of the preseut time. The general ab-
sence of such material has led to the '
occasional use of these ancient deiws-
.. „ , . . 1 . . Fio. 25.— S«lion thmnKh cmil bod. o. bed rook;
its as fire clay, i. e., materials wluch b. uudsr-ciayoTuicientwiUi b: pwitioniDwhii-ii
will endure without melting the i™=<>iid«<iH«"o™^ ■^u^e^rf™u; d,»nd.
" ■loDB or other bedded rock -. t, TohU treo, with
high temperature to which they are twim id imduri^iB;.
exposed in liimaces. In any ordinary soil a wliite heat will cause the
eiliceons element of the deposit to !nelt, for the reason that the lime,
potAsb, or soda which it contains will combine with the silica when the
mass is greatly heated, thus forming a g1a«s or cinder. It is not likely
that the present condition of tlie Carboniferous soils is that which they
exhibited when plants first began to grow upon them; at that time they
may have had the usual share of alkaline substances ; but the very con-
ditions which made these soils the seat of swamps secured the surface
on which they lay Iroro wearing downward in the manner common in
ordinary districts, and so prevented the constant renewal firom the
underlying rock of the materials removed by vegetation. The result was
that in time the earth below tlie swamp accumulation was deprived of
the matter which coold be removed throagh the action of plant roots.
So far as these plants by their conditions of growth could take up sol-
uble minerals of the soil, they removed them, storing the matter in their
stems and leaves. When the plants decayed their waste fell into the
peaty accumulation and gnidually the mineral matter became leached
out and conveyed away to tlie sea. As there was no means of restoring
plant food, the soil gradually lost the jiower of contributing to the growth
of plants. Thus while in the case of ordinary upland soils the process
of decay in the underlying rock continually adds to their fertility, while
the waste of vegetation is constantly returned to the earth, in most of
these swamps of the Carboniferous time, on the contrary, all the condi-
tions serve to pauperize the layer. Owing to various causes, however,
some of which are to be noted hereafter, the soils beneath our modem
swamps do not in the same complete manner undergo the process of
exhaustion.
It is probable that the progressive removal of the soil matt«r from
beneath the swamps of the Carboniferous jwriofl had nmch influence on
the development of the peaty material whicli in time became convert«id
into coal. The larger part of their carbonaceous material was formed
from the waste of plants which rcqoii'ed a certain amount of mineral
8HALEB.] ORIGIN OF PRAIRIES. 323
matter for their support. This the plants had to obtain through their
roots. After the swamp attained a certain thickness, the continual
leaching away of these substances would gradually limit the growth
of the plants which tenanted the morass, and finally the growth might
be entirely arrested by lack of such material to supiK)rt the vegetation.
PRAIRIE SOILS.
There is another important group of soils which owe their peculiarities
not to any excess or insufficiency in their water supply, but to the cir-
cumstances of their geographic situation and organic history. These
are the prairie lands of the Mississippi Valley, and the similar soils
which are found in various parts of the world. The origin of the prairies
of this country has been a matter of much discussion, and many theories
have been advanced to account for their existence. In the state of
nature from which they are now rapidly passing, these wide fields were
generally unforested rolling plains with scanty woodland growth,
which was mainly limited to the neighborhood of the streams, while
their surface was covered by a dense and rank herbage of annual
plants, mainly grasses springing each season from perennial roots.
Along the banks of the permanent streams and in swales of their surface
there were strips and patches of woodland, but it was often possible to
journey for a day without seeing a tree. This untimbered country was
in marked contrast with much of the neighboring land. Thus a large
part of Michigan and Ohio and portions of Indiana were densely
wooded, and these districts lie on three sides of the extensive prairie
district which existed west of the Mississippi River. The soil of these
prairie lands generally afforded a combination of mineral and organic
matter exceedingly well suited to grain crops, so that when subjugated
it yielded ample returns to tillage.
Among the several explanations by which it was sought to account
for the treeless yet fertile nature of the prairies we may note the two
which seem most important. It has been held that the prairies owe
their unforested condition to the exceeding fineness of division which
characterizes their mineral material, it being supposed that such com-
minuted matter was unfavorable to the growth of trees. This does not
seem to be a reasonable supposition, for we find that when occupied by
civilized man the prairie soil will nurture a great variety of trees quite
as well as any other soil. There is therefore no reason to suppose that
the condition of the soil can in any way account for the failure of the
forest growth to take or keep possession of these districts. It has been
supposed by some that these prairie districts have recently been occu-
pied, in large part at legist, by great lakes, the extension of the fresh-
water seas such as Michigan and Erie, or perhaps other basins of the
northwest. While it is probably true that a considerable portion of the
prairie districts have been thus recently submerged, it seems certain
that this fact can not in any way account for the absence of forests, for
324 ORIGIN AND NATURE OF SOILS.
the reason that a large part of the area in northern New York, Ohio,
and Pennsylvania was also recently occupied by extensions of the great
lakes which lie in the vicinity, yet these regions are abundantly tim-
bered. It seeins therefore certain that the forest trees have had time
to return to the prairie district, especially as there are scant patches of
varied wood along the streams and other wet places in prairie districts.
The most essential peculiarity of prairies consists, as is well known, in
their treeless nature. This feature may be well explained in the follow-
ing simple way : The region they occupy is characterized by ^riods of
enduring drought, which reduces even the forest-clad portions of the
country to conditions of extreme dr>iiess. At such times forest fires
will spread with great celerity and extend to vast distances ; even in the
relatively humid districts of Michigan such conflagrations, though op-
posed by all the arts to which the settlers can resort, often extend for
scores of miles. The native Indians of this part of the country were in
the habit, through carelessness or design, of firing the prairie grasses
every spring. Such fires swept like a wliirlwind over the plains and
were rarely interrupted in their ravages by broad rivers or by swamps.
They would extend into the margins of the forest, and if the vegetable
mold was not very retentive of moisture would result in the destruction
of all young trees in the wood. In pine woods such fires would destroy
all the vegetation with which they came in contact.
It is likely that in the far West, near the foot of the Rocky Mountains,
where the climate after the close of the glacial i>eriod became excessively
dry, the soil may have ceased to bear forests because of its arid nature.
The process of burning may then have extended the prairie country to
the eastward until the condition of open ground was brought into dis-
tricts where the amount of rainfall was sufficient to maintain forest
trees.
Evidence that this timberless character of the plains east of the
Mississippi river has been brought about by the spread of fires is afibrded
by the conditions which existed in Kentucky during the latter part of
the last century. While the Indians used this region as a hunting
ground, the district between Louis\ille and the Tennessee line, extending
thence westerly along the southern border of Kentucky to the Cumber-
land river, was mostly in the condition of prairies. Except near the
streams and on the margin of this so-called "barren district," the for-
ests were scarred by fire. There were no ytmng trees springing up to
take the place of the old and thick-barked veterans of the wood, which
from the hardness of their outer coating could resist flame. When these
mature trees died they had no succession, and so the prairie ground
became gradually extended over the area originally occupied by forest.
After the Indians were driven away about 50 yetirs elapsed before the
country was generally settled, and in this i>eriod the woods to a con-
siderable extent recovered jKissession of the areas of open gi'ound. The
periodic firing of the grass having ceased, seeds were disseminated firom
snALEB.] FERTILITY OF PRAIRIE SOILS. 325
the scattered clumps of wood, and soon made tbem the centers of
swiftly spreading x)1antations. It was the opinion of the late Senator
Underwood, of Kentucky, who had seen this country in the first years of
the present century and who was a most intelligent observer, that the
timberless character of this district was entirely due to the habit which
the aborigines had of firing the grasses in the open ground.
It is an interesting historical fact that the first settlers of the country
deemed the untimbered limestone lands of western Kentucky infertile,
and therefore gave to them the name of "barrens." They were led to
the conclusion that these lands were sterile by the fact that in their
previous experience the only untimbered lands with which they had
come in contact were unsuited to agriculture. It is not likely that the
Americans or their British forefathers had ever seen any soil which was,
before it was subjugated, in anything like the condition of the prairie
lands, unless it may have been inhospitable fields near the se^^hore or
certain small areas of a fertile nature in the Shenandoah Valley, which
had been deforested by Indians, probably also by means of fire. Several
years passed after the settlement of Kentucky before the true character
of the so-called "barren" lands was ascertained and they were found to
be generally of a very fertile nature. Meantime young forests rapidly
extended and much of the country which was in a state of prairie had to
be stripped of this woodland growth before it was ready for the plow.
The extremely fertile nature of prairie soil when it is first tilled is
easily explained. Owing to the generally level character of the district
occupied by these open lands the soils were deep, for the reason that
they did not have the chance to slide down to the streams in the man-
ner which we have seen to be common in hilly districts. The frequent
burning of the rank growth of vegetation constantly returned to the
soil large amounts of potash, lime, soda, and phosphatic matter in the
soluble form which is suited to the needs of grain-giving plants. As
the deposit lay on nearly flat surfaces and the rainfall was moderate in
quantity, the ground water did not bear the soluble materials away to
the stream as rapidly as they were formed. The result was that when
these prairie regions were submitted to the plow they yielded in a few
years the store of plant food which had been garnered during many
centuries of preparation. Unfortunately, their-primal fertility has not
proved very enduring; the layer of fruitful earth is generally of only
moderate depth, and with the reckless agriculture which commonly
characterizes this country they have been in most cases within 30 years
brought to a state where they aftbrd only a moderate return for the
labor bestowed upon them. The crops of wheat which originally were
30 or 40 bushels to the acre are, after a generation of culture without
artificial replacement of fertilizing materials, reduced to an average of
about 16 bushels. It should be noted, however, that even where the
original fertility of these prairie soils has been materially diminished
they are readily restored to something like their pristine condition by a
326 ORIGIN AND NATURE OF SOILS.
proper system of tillage, in which deep plowing and a reasonable nse of
fertilizers alike find a place.
The effect of the vegetation which occupied the prairies for many
centuries before the coming of white men was to draw the soluble por-
tion of the fertilizing substances to the upper part of the soil, and to
leave the subsoil unaffected by any of that i>eculiar work which is ac-
complished by the strong roots of forest trees. These, as we have seen,
tend to draw mineral substances from the deeper portions of the subsoil
and from the bed rocks, accumulating the material in the growing veg-
etation, whence its return to the upper part of the soil by process of de-
cay. Much can be done to help these soils by deep plowing and by the
the process known as subsoiling, whereby deeper layers are opened to
the access of air. In a word, we need to imitate in the prairies the pecu-
liar task which has been performed in most districts by the roots of trees.
WIND-BLOWN SOILS.
Last among the soils of peculiar history we may consider those where
the mineral materials have been brought to their position by the action
of wind. In most countries this group of soils is of small importance,
and in fTorth America the blown-sand areas do not occupy in the aggre-
gate more than two or three thousand square miles of surface. The
most easily recognized accumulations of this class are those which form
along the seashore, where winds blowing inwardly to the coast carry the
dry sands from the beach and deposit it in the form of hill-like masses,
termed << dunes." These heaps of blown sand often march slowly and
with a variable movement far inland. The blast of the wind drives the
grains up the moi-e exposed side and over the summit, where they drop
in the lee of the mass of the hill. These ^< dunes" sometimes rise to the
height of one or two hundred feet above the base. Wherever they are
formed on open ground they have a ridge-like character, the long crest
lying transverse to the direction of the prevailing winds. Where the
dry sand enters the forest lands the accumulation is often in a more
sheet-like form, and this because the close-set trees destroy the move-
ment of air currents. (See Fig. 13.)
When they first start from the shore the dunes are usually composed
of very clean sand, the grains of which are of about the same size in
each layer of the deposit. The material is of a finely divided nature,
but occasionally the stronger winds convey to the mass pebbles as large
as ordinary peas. As the dune advances farther from the shore they
come iuto a region where the energy of the storms is rapidly diminished
by the friction of the air upon the surface; the pebbles are then left
behind in the path of the dune and only the finer materials are con-
veyed onward. As this motion of the marching sands is usually at the
rate of a few feet each year, the matter is partly decomposed by the
action of air and rain, so that vegetation finds a chance to take root upon
8HALEB.) BLOWN SANDS OP DESERT REGIONS. 327
it. As the living mantle grows tliicker it gradually restrains the action
of wind, until finally the mass is brought to rest.
Migrating sands are formed not only along the seashore and along
the shores of the greater lakes, but also beside the banks of rivers,
which cut through deposits of glacial drift, where the sands have been
separated from the clay. Thus some of the most extensive, or at least
the most widespread, dune deposits occur along the eastern sides of the
greater New England rivers, as for instance in the district bordering
the Merrimac, between Nashua and Concord, New Hampshire. They
are less conspicuous and characteristic beside the rivers in these dis.
tricts, for the reason that the areas are generally forest-clad, and so the
deposit appears in the form of a broad sheet accumulated between the
trees.
As compared with Europe, deposits of blown sand in the form of
dunes are relatively rare on this continent, because on the eastern coast,
where alone sandy shores abound, the prevailing winds are from the west
and air currents thus serve to prevent the extension of the blown de-
XK)sits for any distance into the interior. A narrow strip of dune sands
borders the Atlantic coast from Cax)e Florida to the eastern end of
Long Island. They are tolerably abundant on Gape Cod and the islands
which lie south of that cape. The northernmost XK>int at which any
considerable deposit of this nature occurs is in Massachusetts, imme-
diately west of Cape Ann. At no point, however, do these dunes extend
for more than about 3 miles inland from the sea, though there are some
lying at points farther inland, accumulated when the seashore lay some-
what farther westward than it does at present. The slight incursion of
these dunes is due to the great violence of wind during easterly gales.
The rate of movement of the storms, however, does not persist for any
distance from shore, and the material thus imported is subjected to the
constant attack of the less violent but more prevalent westerly breezes.
The most important interior deposits of dune sand are found along
the borders of the great lakes in the Laurentian system of waters. Of
these the largest and most interesting area lies at the south end of Lake
Michigan.
Although a portion of the sand included in these dunes has been de-
rived from the existing beach of the lake, it is probable that the greater
portion came from the ancient shore of that water which, during the
last or Pleistocene geologic epoch, lay at a higher level than at present.
Similar deposits of blown sand, essentially like dunes in origin, though
commonly of a more sheet-like nature, are apt to be formed in regions
where the surface is covered with fine debris, but where there is not
enough rain to support a vegetation sufficiently luxuriant to protect the
detritus from the action of wind. This is the case in the Sahara and
other deserts, where a large part of the detritus was formed on ancient
sea floors or accumulated when the climate permitted the construction
of soils, but where the arid conditions now prevent the growth of plants.
328 ORIGIN AND NATURE OF SOILS.
In sucli desert regions the winds are continually bearing away large
amounts of sand and other finely divided rocky matter which accuuiu-
late in marching dunes within the desert region and often invade the
better watered countries on it« margins. Thus the sands from the
Sahara, marching before the west winds, have already entered and dev-
astated considerable portions of the valley watered by the Nile. The
general eflfect of these movements of air-driven detritus is to impoverish
the surfaces which they cover. The deposits themselves, owing to their
very siliceous nature and their extreme permeability to water, are of
little service to plants, and therefore are worthless for the uses of man.
It should be noted that the dunes formed by the disruption of soils
which, though once well wat^^red, have through climatic changes become
extremely arid are less infertile than are those which are formed from
the coast detritus. The reason for this is readily seen. While the
coastal sands have by washing been deprived of all their clayey matter
and are thus generally of a nearly pure siliceous nature, the detritus of
the desert contains a large part of the finely divided and fertilizing
materials which belonged to the soil before it was broken up. Owing,
however, to the action of the wind, this finer material is commonly
driven to a much greater distance than the coarser debris. The
result is that in many of the desert areas in the Cordilleras the pul-
verized rock matter has blown away from the surface leaving a sheet
of pebbles and other rock fragments where there was once a distinct
soil. In the eastern iK)rtion of Asia, about the head waters of the great
rivers of China, there are vast accumulations, sometimes a thousand
feet or more in thickness, composed of fine dust which has blown from
the desert area of that continent into the more humid region of the
eastern part of the continent. The masses accummulate in the form of
a table-land, sometimes filling deep valleys which were excavated in a
time before the dust invasions began. Deposits of less extent and
thickness essentially like those in China have been formed by the
migrations of dust in several other parts of the world. In the western
Mississippi Valley, especially in the northern portions of that area, are
considerable accumulations of fine grained detritus evidently brought
from a great distance. This material is commonly known as loess; its
origin has been a matter of much debate, but it seems likely that it is in
part at least due to the action of the wind blowing the fine detritus
from the region about the eastern face ofthe Cordilleras into the central
portion of the continental valley.
In larger part, however, the loess of the Mississippi Valley probably
owes its origin to conditions which existed during the last glacial period,
when the region in which it lies received the fine flour-Uke sediments
ground up beneath the ice and borne forth to the margin of the glacier
by streams of fluid water which flow beneath such ice masses. This
fine-grained and therefore easily transported detritus appears to have
been distributed over wide areas adjacent to the main stream in the
8HALBB.] EFFECT OF man's ACTION ON SOIL. 329
northern part of the great valley. As these soils, which owe their
origin to drifting dust, are generally formed by the descent of the
particles into interspaces between the growing vegetation much in the
manner in which it accumulates in alluvial terraces, the mass commonly
takes on a horizontal distribution well suited to the uses of agriculture.
The mineral substances of which it is composed are usually much oxi-
dized before they enter on their journey, and owing to the way in which
they are laid down amid the growing vegetation they become thor-
oughly mingled with decayed vegetable matter. Thus while the march
of the wind-driven soils is in an immediate way devastating, the move-
ment of the lighter part of the debris may be advantageous to the soil of
the districts in which it comes to rest.
None of the dune deposits in this or other countries have any value
for tillage purposes. In fact their only human interest consists in the
dangers which they may bring to fields and habitations. In Europe
this is often serious. In the region at the head of the Bay of Biscay
an extensive territory has been covered by these sands and reduced to
a state of sterility. It has required a large amount of official care to
restrain the march of these blown sands in that part of France. In
eastern England a considerable village known as Eccles was, more than
a century ago, overwhelmed by the vast marching dune. So thick was
the accumulation that not only were all the houses deeply covered, but
the parish church was buried beneath the mass. After more than a
century of inhumation, the subsequent march of the wandering hill has
begun to disclose the houses of the viUage, and it seems not improbable
that in the course of another century the heap may pass by the site of
the town.
We have now completed our general survey as to the eflfect of the
varied conditions which operate in the formation tod preservation of
soils. This account is incomplete as regards details, but it is to be
hoped that it may give the reader a general idea as to the balance of
the organic and inorganic actions which affect this admirable life-giving
coating of the earth, the zodc from which all the higher life springs
forth, and to which, after the appointed term of existence, it quickly
returns. We have seen that the adjustment of these conditions per-
mits the soil to form and do its appointed work in varied states of the
earth's surface. We have now to consider some of the effects of human
culture on the soils, and also in a measure the reactive effect of this
envelope upon the estate of man. In this field of inquiry we shall find
a large and varied set of problems which can be considered only in a
very general way.
ACTION AND REACTION OF MAN AND THE SOIL.
The primitive men, at least in their savage state, had very little in-
fluence on the soil — much less, indeed, than many species of lower animals.
As long as men trusted to the chase, to fishing, or to the resources af-
330 ORIGIN AND NATURE OF SOILS.
forded by wild fruits and grains for their subsistence, and to chance
stones picked up along the stream for their weapons, they were practi-
cally without influence upon the soD. When, however, our kind took the
first long step upward in the arts and began to till the earth, a new and
momentous influence was introduced into the assemblage of soil condi-
tions. Even in its simplest form tillage requires that the natural coating
of vegetation shall be stripped away in order that the plants which have
been selected for culture shall have entire control over the nutriment
which the earth affords. Agriculture, moreover, requires that the soil
shall be overturned in order that plants may in the open textured earth
have a better chance of pushing their roots easily and swiftly through
the mass in search of food. Both these processes are exceedmgly sub-
versive of the original conditions of the soil. They manifestly tend to
break up the adjustments by which the deposit is created and preserved.
While in the wild or natural state the surface is generally covered by
an assortment of trees of varied species, as well as of lesser undergrowth,
the roots of which are always deepening the detrital layer and winning
new and lower-lying stores of nutriment. Moreover, in this condition
the earth is well protected from the detrimental action of the rain by a
coating of decayed organic matter which is constantly working down
into the true soil.
In its primitive state the soil is each year losing a portion of its nu-
trient material, but the rate at which the substances go away is generally
not more rapid than the downward movement of the layer into the bed
rock. Thus from age to age the detrital mass, save by unusual accidents,
{s neither thinned nor impoverished. But when tillage is introduced,
the inevitable tendency of the process is to increase the rate at which
the soil is removed until the destruction begins to trench upon its depth
and fertility. When mantled with its coating of vegetation, which in
its natural state is never violently disturbed, the earth yields to streams
only that part of dissolved matter not seized upon by the dense tangle
of roots, which in most cases occupies the whole of the detrital layer.
Except for the undissolved sediments worn away along the banks of the
stream or the shores of lakes and seas, no part of the soil, while it re-
mains in its normal condition, goes away in the state of mechanical
suspension.
K the reader would acquire a distinct eye impression of the difference
between the conservative conditions which prevailed in the soil before
man's interference and the destructive state which exists afterward, he
should during a time of continued rain resort to some of the numerous
valleys of the Appalachians where the country is but partly subjugated
by man. lie will there observe that the streams which drain the dis-
trict where tillage prevails are charged with a burden of detritus won
from the soils. This is shown by the reddish yellow hue it has imparted
to the water flowing from the valleys where tilled lands lie. While most
of the tributary brooks send out such turbid waters to the main stream.
r
is-n
• E§
8HALBB.1 EFFECT OF CULTIVATION ON SOILS. 331
we here and there And one which, though swollen by the rain, lacks all
such colormg matter. The stream is either pellucid, or, if stained, has
the brown hue which decayed vegetation may impart. On investigation
it will always be found that streams which flow clear water drain from
vaDeys in which the primitive forest is unbroken, while those charged
with a load of detritus are from districts where there are extensive tilled
fields. After a little practice in observation it is possible from the share
of mud in the waters of a brook to tell how far the clearing away of the
forests has extended in the valleys whence it flows. Where, as in the
valley of the upper Missouri, the vegetable coating is extremely incom-
plete, owing to the present arid state of the country, the torrents which
form in times of rain may, from the ease with which they wear the un-
protected surface, convey large amounts of detritus in their waters.
This, however, is an exceptional condition of the natural soil (see PL
XXX).
In this country, where the lands have been tilled for a relatively short
time, the evils arising from the waste of soil when it is bared of vegeta-
tion are not so pronounced as in many parts of the Old World, where
extensive districts have to a great extent been devastated by this action.
Thus in many parts of the Mediterranean region, particularly in Italy,
the soil upon the slopes of steep MLlsides, which once bore luxuriant
forests, and which might with due care have been made the site of rich
pastures and orchards, are now reduced to the state of bare rock. In
the region immediately north of Florence there are upland districts where
it is possible to walk for miles without setting foot on anything in the
way of soil which has any arable value whatsoever; yet in this section
but a few centuries ago there was a thick layer of fertile forest mold,
which, when the woods were swept away, was quickly washed down upon
the plains or into the sea.
The effect of the extensive culture of European soils is shown in the
proportionately large amount of waste carried out in the form of mud by
streams which drain that country. The Ehone and the Po, which flow
from two of the most completely tilled districts of the world, discharge
with their waters enough detritus to lower the surface of the country
which they drain to the amount of about 1 foot in each thousand years,
while the Mississippi, which drains from a valley as yet imperfectly tilled,
carries to the sea only about enough detritus to lower the surface by one
foot in 7,000 years. Although the evils arising from the washing away
of the soil in America have not as yet been very serious, a close reckon-
ing of the loss would , probably show that it already amounts to the
practical destruction of that coating over an area some thousands of
square miles in extent. These depauperated districts lie almost altogether
in the region to the south of the glacial belt, and mainly in the hUly
portions of the so-called Southern States, especially in Virginia, the
Carolinas, Kentucky, Tennessee, and Mississippi. There is scarcely a
county in these States where it is not possible to find a number of areas
332
ORIGIN AND NATURE OF SOILS.
aggregating from 300 to 500 acres where the true soil has been allowed
to wash away, leaving exposed to the air either bare rock or infertile
subsoil. Where subsoil as well as the truly fertile layer has been swept
away the field may be regarded as lost to the uses of man, as much so,
indeed, as if it had been sunk beneath the sea, for it will in most instances
require thousands of years before the surface can be restored to its
original estate.
Where tillage, without due care for the needs of the soil, has led to the
destruction of the superficial layer, while the subsoil is retained, the
damage is remediable, provided pains be taken to smooth over the
ridges and furrows with which the earth is seared, and to clothe the
surface in grass. Those who find themselves charged with such care
will do well to observe what happens when any steep sloi)e is deprived
of its forest covering and is left unprotected by such a coating as is
formed by grass roots. As soon as a surface of this nature is laid
bare, the rain, gathered into rills, begins to cut in the manner of moun-
tain torrents, the separate channels often being separated from each
other by intervals of only a few feet. As long as the beds of these riv-
ulets are in the friable earth they wear rapidly downward, and thus keep
Fio. 20.— Diagrammatic Bection sbowing proeeaa of formation and cloaing of gullies on hillsides.
a a, original surface ; b b, gnlUed surface ; e e, original outline of gullie» ; d d, outline of healed surface ;
ee, detritus washed into gullies; gg, vegetation serving to retain detritus.
the sides of their little valleys very steep; they often, indeed, form an
angle of 30° or more in inclination. The earth when moistened slips
down these declivities with such speed that no vegetation has a chance
to take root upon them, and so the process of degradation may go for-
ward at the rate of several inches a year. Where certain species of
trees or bushes, such as willows, are naturally or artificially planted in
the furrows in so close-set an order that they may cheek the rapid cur-
rents, and by their roots prevent the down-cutting of the streamlets, the
erosion may be checked and in a few years the surface will again be-
come smooth. The mode of this a<»tion is indicated in the accompany-
ing diagram, which represents successive stages which have taken place
in a rain-furrowed field in the limestone district of northern Kentucky
in a term of 10 years (see Fig. 26 and PI. xxx).
It is most important that the conditions of this rapid erosion, which
is likely to take place on a large part of the lands of the earth, should
be clearly understood and its ccmsequenc^s distinctly apprehended.
The prime cause of this danger is due to the reckless effort to win for
11
HHALEE.] AREA OF ABANDONED FIELDS. 333
plow-tillage land which is fit only for other and less unnatural forms of
culture. Wherever the inclination of the slope exceeds about 5° of
declivity (or one in twelve), except where the soils are remarkably per-
meable to water, it may in general be said that justice to mankind
demands that the field be as far as possible exempted from the influence
of the plow. Such land should be retained in grass or in orchards, or
used as a nursery for timber.
Although our land is still almost of virgin fertility, a heedless neglect
of our duty toward it has led to the destruction of the soil over an
aggregate area of probably not less than 4,000 square miles. This
means the loss of food-giving resources which would be sufficient,
with proper care, to support a population of about one million people.
Besides this annihilation of the earth resources in the area where the
soils have been allowed to wash completely away, a vastly more im-
portant though less visible damage has been done by the partial de-
struction of the nutritive layer, in the course of which it has been thinned
and worn to a point where it will no longer pay the cost of tillage.
When brought into this impoverished condition it is, in the common
phrase "turned out," or, in other words, committed to the slow process
of redemption which the natural agents of soil-making may bring to
bear. It is fortunate that over the most of this country, perhaps over
three-quarters or three-fifths of its tillable land, the surface has such a
gentle inclination, and the native grasses form so firm a sod, even on
exhausted land, that these abandoned fields do not wash away, but are
allowed slowly to recover from the brutal ill usage to which they have
been subjected.
The total area of these abandoned fields which lie in the States of
Virginia, Tennessee, and Kentucky alone amount, according to the
estimate I have made with some care, to between five and six thousand
square miles, or about one-thirteenth of the total tillable surface of
these States. Taking the lands of the United States as a whole and
basing the estimates on numerous local inspections of the conditions of
diverse areas, I am satisfied that at least five per cent of the soils which
have in their time proved fertile under tillage are now unfit to produce
anjrthing more valuable than scanty pasturage. The ave^rage impover-
• ishment of the area which has been subjected to the plow is not to be
computed; but from the statistics of grain production, as shown by the
successive censuses of the country, it seems not unlikely that it amounts
to 10 per cent or more for the whole country. It is greater in the South
and in the new States of the Mississippi Valley than in the eastern
portions of the Union, because careful tillage has long been made possi-
ble in the last-named section by the high price of farm products. •
A portion of this waste of our soils has been inevitable and not
blameworthy, for it has been due to the rapid extension of the popula-
tion over districts so remote from markets that it was only by methods
of tillage which taxed the earth to the utmost, that any profit could be
334 ORIGIN AND NATURE OF SOILS.
had from farming. We have, indeed, thus paid away much of our
birthright in the fertility of our soils as the price for a swift expansion
of our population. Although there may be a certain justification, as
above noted, for a jwrtion of our soil -wasting, a larger part of it has been
brought about by an ignorant neglect of certain simple but inexpensive
precautions which to a great extent would have saved the ])rogressive
decline in the productive value of the earth. Although these precau-
tions are almost self-evident, it may be worth while to set them clearly
and briefly before the reader.
First of all, every husbandman should clearly understand that the
process which he follows in obtaining crops from the soil is essentially
unnatural. In the state of nature all that the vegetation takes from
the earth is promptly returned to it by the processes of decay. There-
fore it is evidently necessary to limit as far as x>ossible the tax laid
ux)on the earth in our artificial treatment of it, and to provide in every
practicable way for the replacement of the substances removed by the
harvests. The details of methods by which the pauperizing of the soil
may be avoided belong in the main to the science and art of agricul-
ture; there are, however, certain questions in relation to these matters
on which the geologist may be allowed a word of comment. The natural
method of preventing the progressive thinning of the soil due to the
material removed by crops and to the washing away of its substance in
the state of mechanical suspension is by deepening the layer of detritus
and making it as open-textured as x)ossible. This end can best be at-
tained by thorough tillage, especially by the process known as subsoil-
ing, whereby the compact lower layers of the soil or even the decayed
IK>rtioiis of the bed-rock, if they be near the surface, may be disrupted
and the matter put in a condition to become dissolved and made avail-
able to plants. In this way, while the surface may still wear down at
a rate much more rapid than when it is forest-clad, the lowering of the
base of the soil may be made to keep pace with it. Moreover, by keep-
ing the detritus near its original thickness and also open-textured, a
larger portion of the rainwater will enter the earth and, moving slowly
toward the open drainage channels, may not scour away the debris. By
this downward extension of the soil the mass of detritus within a given
area which can yield plant food is likely to be increased, and so the
earth becomes better fitted to the peculiar drain which tillage imposes
on its mineral stores (see PI. xxxi).
Our common method of shallow plowing continued year after year to
the same depth tends to create a few inches below the surface an arti-
ficial hardpau formed by the pressure of the base of the plow. At best
this instrument of tillage is a rather clumsy contrivance for the end it
seeks to accomplish : its action is that of a wedge driven through the
earth, which divides and overturns the soil above the share while it
compacts and smears the lower portion over which it slides into a mass
which, if the material be at all clayey, as is the case with all good soils,
8HALBB.1 EFFECT OF CROPS ON SOILS. 335
becomes in a few years almost as impervious to water as a roof. The
result of this action of the plow is to limit the penetration of the rain-
water to the upper part of the detritus, which is loosened by tillage,
and also to prevent the x>enetration of roots and increase the danger of
the materials washing away.
These evils may be in a great measure avoided by a few simple expe-
dients. When only the common plow can be used, the depth of the fur-
row should be varied from year to year so that the compressed level
where the heel has trod may often be broken up. Where xwssible some
subsoil-breaking implement should frequently be used to open the lower
portion of the detrital layer to the entrance of water and of roots.
Among the many means by which these ends may be attained we note
the familiar device of sowing certain crops, such as red clover, the
plants of which have strong tap roots; these, save in very compact
earth, will penetrate to a greater depth than that to which the plow is
ordinarly driven and thus serve to make water ways and paths for the
roots of weaker species into the subsoil.
Although a certain amount of gain may be had by varying from
season to season the depth to which the plow is set and a yet greater
advantage from subsoiling, every description of plow is more or less
injurious to the soil through the smearing and compacting action which
it inflicts upon it. It is a most unfortunate limitation of agriculture
that spade tillage is so much more costly than that accomplished by
the plow. One of the greatest desiderata in connection with our farm-
ing is an instrument which will overturn the earth in the manner of a
spade — that is, without compacting the lower portions of the deposit
in order to overturn the upper parts. No one who has carefully com-
pared the condition and product of fields which have been long tilled by
these two instruments, the plow and the spade, can doubt the destructive
eflfect of the first-named tool. There seems to bo no essential mechanical
difftculty in the way of the inventor who would seek to produce an in-
strument which would delve the earth as does a spade. The amount of
power requisite to effect the overturning should certainly be much less
than that expended in the rude rending work which the plow effects.
It is a common practice to remove all or nearly all the woody matter
of our crops from the soil on which it has been produced. The result
of this process is that in a few years the earth comes to lack that share
of decaying organic substance which its normal functions require. It
should be remembered that in the state of nature soils have commonly
from 6 per cent to 20 per cent of their mass composed of such organic
debris; any considerable decrease in the amount of this material will
more or less completely arrest the processes by which mineral sub-
stances are gradually brought into a state in which the plants can make
use of them. The introduction of this organic debris is partly accom-
plished in tilled fields by allowing the weeds and other wild plants to
occupy the surfisbce during a period of fallow. The waste from this
336 ORIGIN AND NATURE OF SOILS.
growth when turned in with the plow serves in a certain but generally
insufficient measure to secure by its decay the conditions necessary for
the solution of rocky matter in the earth. When, as is often the case,
this vegetable waste is burned before the ground is plowed, although
the mineral materials are returned to the soil in the form of ash, the
principal end is not attained. The only really effective way of main-
taining the due share of organic matter in soils is to plow in well chosen
green crops. Even where, as on a small portion of our American fields,
barnyard manure is occasionally used, the quantity of vegetable waste
thus introduced into the soil is likely to be inadequate.
Wherever there is a considerable exportation of crops from any dis-
trict it is impossible, save with extraordinary care, to avoid a diminu-
tion in the fertility of the soil! The sale of each bushel of grain or
other product of the fields permanently removes a part of the resources
of the earth. However carefully the barnyard and other manures may
be gathered and returned to the field, this progressive waste is inev-
itable. If the soil retains its fertility it is because of its speedy descent
into the underlying rocks. The rate at which the exhaustion proceeds
is generally in proportion to the immediate success of the agriculture.
Farming is, in general, a process of selling the birthright of those who
own the land.
A century ago it would have seemed to a considerate observer aware
of the principles above laid down that the progressive decadence of our
soils was something which could not be contended against, and that
the process was sure in the end to bring every land to the state in
which its food-producing resources would be exhausted ; but within the
last 50 years we have learned to seek in the mineral kingdom for vari-
ous chemical substances which are removed from the soil by crops, and
which may thereby be returned to it in quantities required to maintain
its fertility. This use of mineral fertilizers, at least on an extended
scale, began with the introduction of guano, the dried waste of bird
life which had accumulated on the islands of a nearly rainless district
off the west coast of South America. Guano appears to have been ex-
tensively used by the Peruvians long before the conquest of the con-
tinent by the Spaniards. It was first brought to Europe and intro-
duced to the attention of agriculturists about the year 1840. Shortly
after that time a very extensive trade in the substance was established,
and in the course of twenty years it led to the substantial exhaustion
of the principal fields of supply. Owing to the increase in the price
of this substance the attention of chemists was called to the jwssibility
of making similar fertilizing materials, using as a basis the geologic
deposits of lime phosphate, soda, and potash. At first this new art
was practiced for the purpose of adulterating the natural guano; but^
unlike a mtyority of such sophistications, it has led to a new and most
important industry — ^that of manufacturing mineral manures.
The greater part of these artificially produced fertilizers consist of a
HHALKH.] MINERAL MANURES. 337
mixture of natural earths coutaiuiiig lime phoHphates, etc., along with
fish- waste, blood, and other materials which afford ammoniacal mate-
rials. It is now, however, becoming clear that excellent manures,
though they act less quickly upon the soil, may be produced altogether
from the mineral kingdom. Even the ammonia required to make com-
pounds the most speedily effective may be obtained from materials
formed in the process of making gas or coke. It seems likely that the
principal ingredient of these fertilizing combinations most required in
ordinary crops and most deficient in soils, viz, the lime phosphate, may
soon be afforded in such quantity that it will be an easy matter each
year to restore to the earth all the substance which is withdrawn by
cropping. So rapid is the present advance in the arts whereby avail
is made of the mineral manures, that we may confidently anticipate the
time when from the rocks of the deeper earth we shall obtain the
means for restoring fertility to all soils- where a reckless neglect of the
fields has not allowed the framework of debris to be utterly destroyed.
The amount of these mineral manures now known to exist is great
enough to meet the demand which would arise if the fertility of onr soils
were to be perfectly maintained by their use for centuries to come, and
it seems likely that we have but begun to discover dexwsits of this nature
which exist in different parts of the world. Within five years, in Florida
alone, areas nnderlaid by lime phosphate have been brought to the
knowledge of the world which contain a sufficient quantity of that ma-
terial to restore the fields of North America for generations to come*
Soda may be had in limitless quantities from common salt, and x>otash
abounds in a number of minerals, such as feldspar, from which the ex-
traction is difficult, and in glauconite or green sand, whence it may
readily be separated. It seems likely that in the progress of art the meth-
ods of preparing this last-named substance from common varieties of
rocks will become cheaper, and so the last of the more indispensable and
most easily exhausted of the fertilizing materials of the soil may be
supplied to the needs of the husbandman. When these mineral manures
come into general and skillful use agriculture will enter on a new stage
of existence; it will no longer be an art so gross in its methods as to
lead as now to a general destruction of the soil, but a science by whose
well devised means the fruitfulness of the earth will be constantly main-
tained and enhanced.
The influence of soil products won by tillage on commercial and other
lines of development deserves a more extended notice than can be given
here. More than any other creature, civilized man has come to depend
upon the earth for a variety of needs, of which the primal and most
important are served by the soil. Although climate, geographic posi-
tion, and the resources of the deeper earth have much to do with the
prosperity of our kind, the character of the soil as regards endurance
of tillage and the crops which it nurtures is of the first importance. It
is impossible for us to consider this matter broadly, but a few instances
12 GEOL 22
338 ORIGIN AND NATURE OF SOILS.
may be given which will serve to show the reader how on this continent
the characteristics of soil have aflFectexl the history of its population in
various regions.
One of the first of the peculiar effects on the history of civilized man
in America brought about by the nature of the earth is found in the
circumstances attending the culture of the tobacco plant. This vege-
table proved peculiarly well suited to the soil of Virginia and Maryland,
and therefore, even in the first century of the history of the colony, it
became the principal staple in their trade with the Old World. On the
returns given by this industry the political and social culture of the
central colonies of the Athmtic coast chiefly rested. To it also in the
main was due the profitable and rapid extension of African slavery.
In a similar manner the soils of the more southern States proved in the
present century well adapted to the culture of cotton, a crop which led
to the establishment of large and numerous plan tuitions, and thus to the
further diflftision and firmer establishment of the slaveholding system*
Though in part due to climatic features, this system by which the de-
scendants of Africans were held as slaves is principally to be accounted
for by the characteristics of the earth i-n southern Stsites. If that part of
the country had been provided with soils like those in New England it
would have had a very diflferent economic and political history.
We i)erceive the effects of soil on the diffusion of slavery in a yet
clearer manner when we examine into the features characteristic of the
local distribution in States in which it was by law established. In the
plain lauds, where the soil is adapted to cott4>n or tobacco, slavery was
dominant, indeed we may say universal; but in mountain areas, where
the small fields could not be profitably tilled by slaves, the institution
never found a place. In eastern Kentucky and in parts of western Vir-
ginia and North Carolina negroes have always been exceedingly rare.
There are populous counties in this region where no member of that
race has ever been a resident either as slave or freeman. This absence
of slaveholders in the hilly and mountainous portions of the South nat-
urally had a great effect in the issue of the civil war which that insti-
tution caused. The people of this rugged country of the Appalachians
did not to any extent sympathize with, and often took up arms against,
the slaveholding (communities of the lowlands. As this nonslaveholding
district almost cut the South in twain, its infiuence on the conditions of
the contest were momentous. Something like the same effect was per-
ceptible in single States. Thus in Kentucky we find that a majority of
the ijeople on the richer lands where it was profitable to keep slaves
were led to cast their lot with their kindred of the same class in other
parts of the South, while those dwelling on poorer soils, where they knew
nothing of the institution, were overwhelmingly on the Federal side in
the debate. It seems almost certain that if Kentucky had been provided
with a uniformly rich soil, suited to large i)lantations, it would have
joined the other Southern States, to the great advantage of the Gonfed-
8HALKR.1 EFFECT OF SOIL ON HISTORY OF MAN 339
mrates and to the 8eriouH injury of the Federal cause. In a struggle so
nearly matched thin difference might have been of decisive importance.
Not only in the doubtful issue of the war but also in the more com-
putable triumfAt^ of peace the character of soil in this country has
greatly influenced the history of its people. A striking instance of this
effect may be noted in the advance of population from the seaboard
district into the Mississippi VaUey. Thus, while it required nearly two
centuries for the English colonies o£ the Atlantic coast to break their
way through the rough country of thte AUeghanies and then through
the dense forests of the lowland region in the eastern part of the Ohio
Valley to the margin of the prairie land of the West, fifty years has
served to win to their uses the yet greater area of the timberless or
lightly wooded country of the Far West. Although something of this
speedy contest must be attributed to the rapid diffusion of railway and
steamboat transportation, yet more is to be allowed to the influence of
the open nature and easy subjugability of the soil in these areas. Itjs
clearly one thing to push forward the frontiers of a civilization where
each acre has to be slowly and laboriously stripped of its timber and, if
it be in a glaciated district, of its bowlders also, and it is quite another
undertaking to extend cultivation over a prairie district where a plow
man may turn a straight furrow for miles away from his starting x>oint.
An incidental but closely related effect of this open state of the land in
the central and western x>ortions of the Mississippi Valley is seen in the
rapid increase of population in this country and the great commercial
prosx)erity which it has attamed. The influence of the breadth of this
region has not only been felt in the States which have sprung up like
magic in the Northwest, but in the Eastern States as well. The popu
lation of the Unites States would probably at the present time be some
millions less than it is if the central part of the continent had been
densely wooded as far west as the one hundredth meridian.
It would be x>ossible very much to extend the citation of these
instances in which conditions of soil have determined, in a certain
measure at least, the history of our people; we can, however, instance
but one other example serving to shpw how even the system in which
the land is held in ownership may be shaped by the character of surface
material. The island of Nantucket, Massachusetts, owing to the fact
that nearly the whole of its area is composed either of glacial moraine or
of extensive sand plains which usually attend these heaps of debris, has,
save in limited parts, a very thin soil not generally flt.for tillage. The
result is that until within a few years the greater part of the land was
held in common, or jointly by the people, each owner being entitled to
a share in the pasturage rights of the area. If he held, for instance,
twelve such rights, he could turn out a dozen sheep to graze on the
uninclosed field. Thus, owing to the nature of the soil, we bad here
perpetuated, in the latter half of the nineteenth century, a form of land
tenure which is a survival from a remote time and represents a gen-
erally disused system of holding real x^roperty.
340 ORIGIN AND NATURE OF SOILS.
EFFECTS OF SOILS ON HEALTH.
The influences of the soil upon the health of man and that of his
domesticated animals, though ]^rhapa less considerable than those
which directly arise from climate, are still of great importance. The
cause and nature of these eflFe('ts are extremely varied and deserve
more attention than they have received. It is only in rec>ent years that
the nature and origin of diseases have been to any extent siccurately
known, and therefore the time of such studies has been brief. It will
therefore not be jmssible to make many definite and readily comprehen-
sible statements concerning this division of our subject.
The action of soils in producing or promoting disease in animals or
man appears to be due to at least three different causes, viz:
First. The quantity of water retained in the earth immediately de-
termines the humidity of the surface of the soil, and this may have a
direct effect on the comfort and health of man and beast.
Secondly. The conditions of this soil water, as well as of the organic
matter mingled with it, have a decided influence on the nourishment of
many forms of bacteria which it is now well known are sources of disease.
The germs of such maladies as cholera, typhoid and malarial fevers,
tetanus or lockjaw, and numerous other maladies appear generally to
require a residence below the surface of the earth before they can
propagate their effects. In fact the larger part of the diseases which
occur among human beings and probably a great number of those
which afflict our domesticated animals appear to be traceable to the
action of certain microscopical organisms that inhabit the soil in the
regions where the maladies occur.
Thirdly. Some influence of the soil upon health is due to the quality
it gives to drinking water obtained from ordinary springs or wells.
Although, for convenience of presentation, we may thus separate the
influence of ground water upon health into these three classes, the
groups are in fact not thus distinct, but are inextricably blended.
One of the immediate effects of excessive humidity of the soil is to
keep the feet of creatures which tread upon it in a condition to favor
disease. Thus sheep in wet pastures are more likely to suffer from
foot diseases than those in dry fields, the continual moisture of the
parts making them a suitable nest for the development of certain germs.
Dwellings of men are made humid by excessive ground water, which also
favors the growth of certain noxious organisms. This is well shown by
the coating of mold which often forms m the lower parts of houses, where
the earth is soaked with water. Although the more common forms of this
growth are not detrimental to health, the circumstances which favor
their development appear to lead to the multiplication of disease-
bringing spores. There are other direct evils connected with excessive
humidity. When the air is very wet, as is the case near very humid
soils, It appears to have a lowering effect on the vitality of men — at
least when they are m certain states of health.
BHALEB] EFFf:CT OF VARYING HEIGHT OF GROUND WATER. 341
From a sanitary point of view the direct effects of excessive ground
water are evidently of small consequence as compared with the second-
ary influences of this e\dl, which are due to the nurture and dissemi-
nation of the germs which it induces. It appears probable that the
spores, by means of which many diseases are propagated, midergo
multiplication altogether in the organic matter contained in the soil.
In the opinion of trustworthy observers the development of these
germs takes place most effectively, and they are most likely to be dis-
charged into the air in those regions where the vertical range of the
ground water varies greatly, esx)ecially during the warmer part of the
year. The reason for this is, probably, that when the vertical oscilla-
tions of the ground water occur the air is alternately drawn down into
and expelled from the interstices of the soil. As this air enters it bears
with it quantities of germs which, descending along with the rainwater,
plant themselves upon decaying bits of animal and vegetable matter
which the earth contains. If, after these spores have multiplied, the
soil water again rises to the surface, it bears the crop with it, leaving
the material on the top of the ground, where it may be scattered by
the wind. When the soil water rises the contained air is expelled and
may also bear with it a share of the noxious materials. Where the
water of the soil remains at nearly a level the germs are not only less
likely to enter the earth, but those which develop there are unable to
escape from their underground prison and i)erish where they grew.
This view of the action of oscillating ground water finds much sup-
port from the experience of men in and around extensive morasses such
as the Dismal Swamp of Virginia and North Carolina. About the
margin of that great area of marshes, where the ground is alternately
wetted and dried to a considerable depth, the people suffer from ague, a
disease which is generally believed to be caused by some species of
germ developed mthin the earth, but in the interior of the swamp,
where the ground water varies little in its height from one season to
another, there seems to be a relative, or, in ca«es, an entire immunity
from this malady. Similar evidence is found in the history of intermit-
tent fever in regions which have recently been subjected to cultivation;
thus in many parts of the Ohio Valley the early settlers suffered much
from this disease, but as obstructions to streams were gradually removed
and wet places drained, so that soil water was no longer brought to the
surface, this disease has to a great extent disappeared. There seems to
be good reason to believe that where the earth has had a chance to
become charged with seeds of disease,, a^ about dwellings and ceme-
teries, any overturning of the soil may lead to the propagation of mala-
dies through the mingling of the spores and the air thus brought about.
In the open fields the same effect on germs of soil are doubtless pro-
duced, but in such localities si)ores probably belong to species which are
not so likely to be harmful to man as those which develop about habi-
tations or in the resting places of the dead.
342 ORIGIN AND NATURE OF SOILS.
1
The health of people in Holland, in the fens of eastern England, and
in similar wet districts in many other parts of the world seems clearly to
show that, whatever be the way in which it acts, a variable level of un-
derground water tends to breed disease, while its x>ermaneut ix>sition,
even if it remain near the surface, is not inconsistent with the good
health of the inhabitants. So long as the fens of England and the
swamps of the Netherlands remained in their natural state and under-
went frequent and extensive changes of water level they were generally
the seats of malarial disease. Now that the drainage system retains
the ground water at about a uniform height these maladies are rare.
In the ideal condition of a tilled district the level of the soil waters
is likely to be favorable to health. The aim of the husbandman is to
maintain the earth in a state where the water rarely, if ever, rises to
the surface. Care as to this point is most desirable, because where water
emerges from the soil or stands upon it the effect is to take away by
the leaching process a much larger amount of soluble materials than
ordinarily escapes by drainage which passes to the stream by way of
the spring. Thus the use of underground drains, which serve to keep
the soil water at a tolerably definite level, is of great advantage to the
earth by restricting the leaching process, and it incidentally serves to
diminish the danger which may arise from the escape of germs.
There is reason to believe that the growth of certain kinds of germs
within the soil is in a way helpful to fertility; it is indeed likely that the
process by which various important substances are brought into a con-
dition to be assimilated by plants is, in certain ways, dependent on the
action of these minute organisms, so that the sx>ore-breeding work of
the soil, which now and then leads to the injury of man, is only an inci-
dental part of what may be an essential function.
There is reason to believe that, owing to the peculiarities of certain
soils, they become especially suited to the development of particular
kinds of germs. Thus in certain districts in and adjacent to Long
Island, New York, the disease known as tetanus, or lockjaw, is of un-
usually common oO/Currence among men and animals. It is the opinion
of experts in medical science that this malady is caused by some si)ecie8
of soil-inhabiting bacterian which invests this part of the country. It
is observed that a wound which is formed by any object covered with
earthy matter is particularly likely to give rise to the disease. Although
this malady has been common in parts of Long Island for many years,
the evil has never spread to the contiguous portions of the shore east
of Point Judith. As there must have been abundant opportunities for
the spread of the germs in this direction it seems reasonable to attribute
their failure to extend to some peculiarities of the soil covering.
The last effects of the soil upon health which we shall notice are those
arising from the use of drinking water derived from this detrital layer.
Injuries from this source are commonly due to the fact that ground water
is usually full of germs of various kinds developed in that part of the
3HAUtB.l CONDITIONS OF DANGEROUS WATER SUPPLY. 343
earth from which the spring or well drains. It may often happen that
the water flows through the earth for a distance of hundreds of feet
before it attains the point where it is taken for use. In the course of
this journey it generally becomes abundantly charged with spores. The
greater part of these germs are innocuous, but if the earth contains the
organisms which produce cholera, typhoid fever, or other ferment dis-
eases, it is quite possible that a very small portion of the soil water can
convey the disease.
Besides the disease-breeding organic germs, ground water also in
many cases contains various mineral substances which may be harmful
to man or the animals which he associates with his life. A familiar
instance of this is found in the eflPects arising from the large amount of
limy matter which exists in the ground water of most limestone dis-
tricts. This substance comes into a state of solution through the
capacity which carbonic-acid gas gives to water for taking up and dis-
solving various minerals. This gas is derived from decaying organic
matter in the soil; but for the presence of this dissolved gas the ground
water would have a mere trace of lime in solution, but owing to its pres-
ence the fluid is able to take up a notable quantity which, though in-
visible, makes its presence evident by the hardness and flat taste which
it imparts. A common eftect of this excess of lime is to produce in
the bodies of men, and sometimes in those of domesticated animals as
well, concretions of a calcareous nature which cause disease. In certain
parts of limestone districts of this and other countries maladies due to
this cause are of very frequent occurrence.
Fio. 27. — Diagram showing one of the ordinary conditions of a dangerous water supply, a, bed-rock ;
b, aoil and other permeable detritus; e, well whence domestic supply is taken; d, dwelling house; e,
cesspool; /, bam; the arrows show the direction in which the soil water moves.
Where the ground water is suspected of being the source of disease,
the evils it entails may readily be avoided by the use of cisterns to
which only the water draining from clean roofs has access. Except in
cases where such a supply is deftled, as by a resort of pigeons to the
roof or by careless construction of the reservoirs which permits the in-
gress of soil water, they afford absolutely safe sources for domestic use.
It seems likely that, with the advance of medical science on the lines
of its present extension, many diseases of a geographical and limited
nature, the causes of which are yet unexplained, will be found to be
attributable to the action of the soil in the regions where they occur.
Thus the peculiar malady called goitre, which is limited to certain moun-
tain valleys, is now by some students explained as being due to the action
of the water which the people drink. In the present state of the science
344 ORIGIN AND NATURE OF SOILS.
of hygiene the only certain point8 of vahie which we have to consider
concern the influence of the soil wat.er on the development and difi^sion
of germs. Where the domestic supply is obtained from the earth it
appears essential to the health of a household that the spring or well
should be so placed that none of the waste from the dwelling, bams, or
stables can contaminate it (see Fig. 27). It appears, furthermore, im-
portant that proi^er drainage should be so arranged that the level of
the soil water is not liable to sudden alteration. Furthermore, it appears
to be undesirable to have the soil near the dwelling overturned while
the house is occupied. This is especially the case where the residence
has been long in use.
Although the distance to which germs may be carried in the under-
ground water is not readily determinable, it may be assumed that there
is no safety in using the flow from a large spring where any part of the
valley in which it lies is occupied by dwellings the sites of which are
above the point of exit. The underground channels of such fountains
often have a very extended and circuitous course; the water ways, so
far as they are carved in the bed rock, are wide open, so that poisonous
matter may in a few hours be transported through them for a distance
of several miles.
If the space of this report permitted, many instances could be given
in which cholera and other fatal diseases had thus been conveyed for
great distances. Springs of sUght creeping flow and ordinary wells
where the water does not enter at one point but seeps in from the side
of the excavation, do not usually drain from a distance of more than
200 or 300 feet from the point where the water escapes. It should, how-
ever, be remembered that there is sufficient evidence to prove that
germs of certain diseases may remain in the soil for several years with
undiminished vitality. These germs may by some chance journey go
unexpected and considerable distances. Where ground water is used
at all for domestic purposes, the only safe way is to take it from a level
above all sources of possible contamination.
man's duty TO THE EARTH.
The foregoing considerations concerning the origin and nature of soils,
though but a brief and inadequate presentation of the subject-matter,
will probably convince the reader that this i)art of the earth which at
first sight seems to be a mere mass of ruin and abasement is re>ally a mar-
velously well ordered and beautiftii portion of this sphere. In it the
celestial and terrestrial energies combine their work to lift the mineral
elements up to the higher planes of sentient life. From it comes the
sustenance of plants and animals, both of sea and laud. The frame of
man is the product of its forces; his form is indexed but a bit of soil up-
lifted for a moment to the noblest shape of life, then bidden to return
to the garner of the earth. Through the ordered and haruionious inter-
action of the complicated forces which effect in the soil the combined
8HALEB.1 SYSTEM OF LAND TENURE. 345
decay of rocks and of organic bodies, materials which seem base and
revolting to many fastidious spirits are made the unique basis of all
sentient existence. When we perceive that civilization rests on the
food-giving capacities of the soil, when we perceive that all the future
advance of our kind depends uxK)n the preservation and enhancement
of its fertility, we are in a position to consider the duty which we owe
to it. This obligation bids us nurture and care for this part of the earth
with an exceeding tenderness and affection. It bids us ever remem-
ber that it is enriched with the dust of our progenitors, and is teeming
with the life which is to come.
In shaping these motives to practice it seems first of all necessary to
clear away those crude and indeed painful notions which lead men to
look with contempt and disgust upon the soil. If there be any of the
great truths of modern learning which more than any others deserve to
be imprinted on the minds of youth, it is these lessons as to the nature
and function of this beneficent part of the earth. Only through knowl-
edge can we hope to bring men to a proper understanding of the value of
the trust which is in their keeping. Until by education we bring people
to a consciousness that the wanton neglect of their duty to their kind
which an improvident use of the soil reveals is a form of treason to man-
kind, we can not hope to implant in them a proper sense of responsibility
in the management of their great inheritance.
It is characteristic of our time that men seek to clear away evils by
means of law. There is a general diocontent with the results which have
been obtained by the system of individual ownership of land and a grow-
ing disx>osition to qualify and limit the nature of that possession. In
considering the questions as to the ways in which the earth's resources
shall be administered, it is clearly necessary to bear in mind the needs
of exceeding care in the preservation of the fertility of the earth. As
long as lands are in the state of forest or prairie, the admirably adjusted
forces of nature wiU insure their preservation. When they become
tilled, it is imperative that they be peculiarly well guarded; any legis-
lation concerning the tenure of land should be devised in view of the fact
that we need to have not less but more personal interest and sense of
responsibility in the management of these problems. It is not proper
here to consider the probable effect of the various proposed modifica-
tions of the land laws. It seems, however, fit that any such changes as
may be made should be planned with a clear understanding of the very
serious nature of the needs. When in the fixture a proper sense of the
relations of the soil to the necessities of man have been attained and
diffused we may be sure that our successors will look back upon our
present administration of this great trust with amazement and disgust;
they will see that a state of society in which men took no care of the
rights which the generations to come have in the earth lacks one of the
most essential elements of a true civilization.
tm
Live Music Archive
Librivox Free Audio
Metropolitan Museum
Cleveland Museum of Art
Internet Arcade
Console Living Room
Books to Borrow
Open Library
TV News
Understanding 9/11