Rivers of North America

Front matter

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CHAPTER I The Disintegration and Decay of Rocks

Mechanical Disintegration — Chemical Disintegration or Rock Decay — Removal and Renewal of Surface Debris.

CHAPTER n Laws Governing the Streams ........ 12

How Streams Obtain their Loads — Transportation — Debris Carried by Ice — Corrasion — Pot- Holes — Lateral Corrasion — Meandering Streams — Other Curves — Deflection of Streams Owing to the Earth's Rotation — Questioning the Rivers — Erosion — Baselevel of Erosion — Peneplains — Influence of Vegetation on Erosion.

Chapter III

Influence of Inequalities in the Hardness of Rocks on River-side Scenery 52

Waterfalls — The Migration of Waterfalls — Bluffs Bordering Aged Streams.

CHAPTER IV Material Carried by Streams in Suspension and in Solution 67

The Visible Loads of Streams — Bottom Load — Measures of Material in Suspension — The Invisible Loads of Streams — Rate of Land Degradation — Mechanical Degradation — Chemical Degradation — Rate of Both Mechanical and Chemical Degradation — Underground Streams.

XIV CONTENTS

Chapter V Face

Alluvial Cones — Talus Slopes — Flood-Plains — Natural Levees — Deltas : Deltas of High-Grade Streams — Deltas of Low-Grade Streams — Effects of Changes in the Elevation of the Land on the Growth of Deltas — Variations in Normal Stream Deposition — Influence of Elevation and Depression of the Land on Stream Deposition — Influence of Variations in Load on Stream Deposition — Influence of Changes of Climate on Stream Deposition — The General Process of Stream Corrasion and Deposition — Profiles of Streams — The Longitudinal Profile — Cross-Profiles.

Chapter VI

Origin of Terraces during the Process of Normal Stream Development — Terraces Due to Climatic Changes — Terraces Due to Elevation of the Land — Bottom Terraces — Delta Terraces and Current Terraces — Glacial Terraces — Relative Age of Terraces — Other Terraces — General Distribution of Stream Terraces.

Chapter VII

Consequent Streams — Subsequent Streams — Ideal Illustration of Stream Adjustment and Development — Examples of Stream Development and Adjustment in the Appalachian Mountains — Influence of Folds in the Rocks on Stream Adjustment — Water-Gaps and Wind- Gaps — Stream Conquest — Ancient Peneplains — Synclinal Mountains and Anticlinal Valleys — Effects of Elevation and Subsidence on Stream Development — Some of the Effects of Elevation — Some of the Effects of Subsidence — Some of the Influences of Volcanic Agencies on Stream Development— Some of the Modifications in Stream Development Due to Climatic Changes — Variations in Precipitation — Variations in Temperature — Fluctuations of Streams — Some of the Influences of Glaciers on Stream Development — Some of the Influences of Vegetation on Stream Development — Driftwood — Superimposed Streams — Migration of Divides.

CONTENTS XV

Chapter VIII Page

Some OF THE Characteris lies OF American Rivers . . . 254

Drainage Slopes : Atlantic, St. Lawrence, Hudson Bay, Arctic, Bering, Pacific, Great Basin, Gulf, and Caribbean — Leading Features of the Several Drainage Slopes — New England Rivers — A Drowned River — Appalachian Rivers — Rivers of Glaciated Lands — Southern Rivers — Alluvial Rivers — The Mississippi — Canyon Rivers — Sierra Nevada Rivers — "Where Rolls the Oregon" — Rivers of the Far North-West — Glacier-Born Rivers — Arctic Rivers — Rivers of the *' Great Lone Land" — Rivers Flowing to Fresh- Water Seas — Niagara — Retrospect.

CHAPTER IX Index 321

ILLUSTRATIONS IN THE TEXT

FIGURE

1. A POT-HOLE BEING SCOURED OUT BY A STREAM

2. A Young Stream near Ithaca, New York

3. Profile of Niagara Falls

4. Cross-Profile of a Floodplain ....

5. Map of the Lower Mississippi showing Crevasses

6. Radial Section of a Delta ....

7. Longitudinal Profile of a Young Stream

8. Successive Changes in the Profile of a Divide

9. Ideal Profile of a Divide

10. Cross-Profile of a Terraced Valley

11. Alluvial Terraces

12. Alluvial Terraces

13. Cross-Section of a Valley with Terraces in Solid

14. Cross-Section of a Current-built Terrace

15. Section of tilted Peneplain ....

16. Sketch-Map, showing Young Streams

17. Sketch-Map, illustrating Stream Development

18. Sketch-Map, showing Mature Streams . ig. Anticlinal and Synclinal .

20. Map illustrating River Piracy

21. Section through Lookout Mountain

22. Map of Chesapeake Bay

23. Cross-Profile of Colorado Canyon Table A. Analysis of American River-Waters etc., Alabama

Rock facing

PAGE

FULL-PAGE ILLUSTRATIONS

PLATE FACING PAGE

I. a. Marion River, New York. b. Ingall's Ceeek, Washington 12

II. Views on the Yukon, Alaska 24

III. a. Ray Brook, Adirondacks, New York. b. Moccasin

Bend, Tennessee River 38

IV. a. Fall on Black Creek, near Gadsden, Alabama, b.

Echo River, Mammoth Cave, Kenjucky ... 60

V. Map of the Delta of the Mississippi 98

VI. a. Sketch of Alluvial Cones, b. Indian Creek, California 102

VII. a. Big Goose River, Wyoming, b. New River, Tennessee, 108 VIII. a. Terraces on Fraskr River, British Columbia, b. Terraces in Connecticut Valley . . . . . 154

IX. Map of the Northern Appalachians 196

X. Map of Western Portion of the Anthracite Basin,

Pennsylvania 204

XI. Map illustrating Stream Adjustment . . . .210 XII. a. Beaver Dam, Wyoming, b. Dam of Drift-wood, West

Fork of Teanaway River, Washington ... 238

XIII. Map of a Portion of the Catskill Moun-^ains, New York, 250

XIV. Map of North America showing Drainage Slopes . . 256 XV. a. Columbia River, b. Hudson River .... 262

XVI. a. An aggraded Valley near Fort Wingate, New Mexico, b. Shenandoah Peneplain, near Harper's

Ferry, West Virginia 26S

XVII. Canyon of the Colorado 274

Chapter 1 The Disintegra Tion And Dec A Y Of Rocks

THE study of rivers, from the point of view of the geographer, necessitates the consideration of the nature and origin of many topographic forms; the reason being that streams are among the most important agencies which give form and expression to the surface of the land. The study of streams, therefore, involves, to a great extent, the consideration of the origin of hills and mountains, plains and valleys, and the changes they pass through.

One of the principal tasks performed by streams is the moving of rock fragments and their transportation to the sea. Another function of streams is the deepening and widening of their channels and valleys. These propositions will be demonstrated later. It will be shown, also, that clear water has but little power to wear away the rocks over which it flows. In order to do this, the flowing water must be charged with hard particles or rock fragments of greater or less size. That is, the streams must be supplied with tools with which to excavate. It is now well understood that the tools used by streams in abrading the rocks are mainly silt, sand, gravel, and stones, which are carried in suspension or rolled and pushed along the bottom. One of the primary questions, therefore, in order to understand how streams are enabled to remove material from the land, and, in so doing, to deepen and broaden their valleys, is: How are the rocks broken or otherwise prepared for stream transportation ?

The soil which nearly everywhere forms the surface of the land is composed mainly of disintegrated rock. This loose surface layer of more or less comminuted and decayed material, much of it, however, far too coarse to be termed soil, is the storehouse from which the streams derive the principal part of their loads.

The study of the agencies at work in breaking and otherwise disintegrating the earth's crust has shown that they may be classified in two groups: 1st, those acting mechanically; and 2d, those whose influence is principally chemical. Although the various agencies in these two groups cooperate and are frequently in action at the same time, it is convenient to consider them separately.

Mechanical Disintegration. — Changes of temperature, as between day and night, or from season to season, cause unequal expansion and contraction of the minerals and grains of which rocks are composed. Various and complex stresses are thus produced which cause even the most compact granite to crumble. The freezing of water contained in crevasses in rocks or in the interspaces between grains or crystals, is accompanied by expansion, which exerts a powerful force tending to fracture and disintegrate them.

DISINTEGRATION AND DECAY OF ROCKS 3

The roots of trees enter crevices in the rocks, and as they enlarge, force off fragments frequently of large size. The undercutting of cliffs and banks by streams and by the waves and currents of lakes and of the ocean, causes the dislodgment of vast quantities of earth and stone. The fall of rocky material produced by these and still other causes, leads to still further breakage. Rock masses are also loosened or caused to fall by earthquake shocks. Volcanoes discharge a great volume of fragmental material into the air, and the cooling of lavas causes them to become fractured and jointed. When molten lava enters surface-water bodies, steam and gas explosions occur, and the rock is perhaps blown to dust. Rain-drops, snow crystals, and hail by beating on the rocks exert a force tending to break off fragments loosened by other and principally chemical agencies, and to wear, and frequently to polish, exposed surfaces. Sand and dust, blown by the wind, on coming in contact with rock exposures, wear away the softer parts and loosen the harder grains and crystals. Glaciers as they flow down mountain valleys or move over the surface of more level land, tear away projecting ledges, and when charged with sand and stones abrade and grind away the rock over which they move. Avalanches and landslides rush down declivities, carrying destruction in their paths, and sweep along loosened rock fragments which are broken still finer and in part ground to powder. The streams themselves, under certain conditions, roll along stones and even large boulders, which become rounded and broken, at the same time abrading the rocks over which they are carried, and thus aid in the general process of rock disintegration which prepares the material composing the land for stream transportation.

All of the agencies just enumerated are mechanical in their action, although accompanied by chemical changes, and are confined to the surface, or, at most, to an extremely superficial portion, of the earth's crust. There are also important mechanical agencies which act deep below the surface and lead to the fracturing of the rocks in such manner as greatly to facilitate the agencies producing disintegration in operation at the surface. And, besides, on account of the continual lowering of the surface in many regions owing to the removal of material, rock fragments originating at a greater or less depth become mingled with those produced at the surface in the several ways just enumerated, and thus become of interest in the study of the manner in which rocks are reduced to fragments of such size that they can be moved by streams.

Of the mechanical agencies leading to the fracturing of rocks below the reach of frost and of normal changes in temperature, the most important are movements in the earth's crust, the nature of which it is impracticable to discuss at this time, which cause even the most massive layers to become folded and broken. These movements are frequently accompanied by the crushing of the rocks in zones of various widths, as when a fracture is formed and its walls ground against each other. Such breaks, accompanied or followed by differential movements of their wails, are termed faults, and the rock fragments produced are designated fault breccias.

The world over and to a great but indefinite depth, the

DISINTEGRATION AND DECAY OF ROCKS 5

rocks are divided by what are known as joints, the origin of which is obscure. These dividing planes are similar, we may fancy, to gashes made by a sharp blade without appreciable thickness, drawn through the rocks. There are frequently two series of joints nearly at right angles to each other, and more or less nearly vertical ; these are intersected many times by approximately horizontal cuts of the same character, and frequently also by planes of bedding. The rocks are divided in this manner into masses that are sometimes nearly true cubes. In many instances the joints cross each other irregularly and divide the rocks into blocks of many shapes. Joint blocks of whatever form vary in size, from a small fraction of a cubic inch to many cubic feet. In some instances these are contributed directly to streams, as when they fall from the face of a precipice, but more commonly they are broken and variously modified by atmospheric agencies before being fed to the flowing waters. The joints in rocks, although of inappreciable width deep below the surface, are planes of weakness along which chemical and mechanical agencies find favourable lines of attack. They open when the rocks are exposed to the weather, and greatly favour the further disintegration resulting from changes of temperature, the freezing of water, etc. The jointing of rocks is one of the primary and most important methods by which they become divided into blocks, thus exposing greater surfaces to the attack of chemical agencies, and in many regions, particularly in rugged mountains and in canyon walls, exerts a direct and pronounced influence on topographic forms.

Among the agencies that lead to the fracturing and mechanical disintegration of rocks deep below the surface, should be noted, also, injections of molten rocks forced upward into the earth's crust, earthquake shocks, the friction of debris carried by subterranean streams, and the falling of cavern roofs. Still another agency, as has been pointed out by G. P. Merrill, in part chemical and in part mechanical in its action, results from the combination of water with certain mineral substances, producing what is termed hydration. This is accompanied by an increase in the bulk of the minerals affected, and the consequent production of stresses in the rocks containing them. In some instances, apparently unaltered rock, when removed from mines and tunnels, rapidly crumbles from this cause when exposed to the air. In nature, the lowering of the surface by erosion and the exposure of previously deeply buried rocks would bring about similar changes. There are yet other alterations in progress in the rocks due to chemical action, that promote mechanical disintegration, which cannot be noted at this time.

By the several processes just enumerated, the rocks are broken into blocks of all shapes and dimensions, some of which are of the size of gravel, sand, and dust grains, and are thus rendered. suitable for stream transportation, and to act as tools by means of which flowing water promotes the process of rock breakage.

Chemical Disintegration or Rock-Decay, — Water is a solvent for probably all substances that occur in the earth's crust, although in many instances acting with extreme slowness. The readiness with which most substances are taken into solution by water is enhanced by an increase of temperature, and in nature is also greatly assisted by various

DISINTEGRA TION AND DEC A V OF ROCKS 7

substances, especially organic acids, with which it becomes charged.

Even rain-water is never pure, but contains various salts and gases derived from the air. Principal among these is carbon dioxide, or carbonic acid. Rain-water on reaching the earth flows over the surface, or percolates for a time through the soil and rocks, and thus comes into intimate relations with the great store of organic acids supplied by the waste and decay of animal and vegetable life. The chemical energy of the water is thus greatly enhanced, and it becomes an active solvent for most mineral substances. Some of the minerals composing rocks are more soluble than others, and, being removed, allow those that remain to crumble and fall apart. The mineral substances taken in solution are, for the most part, contributed to streams and by them carried to the sea as an invisible load ; but a portion is taken below the surface by downward-percolating waters and undergoes many changes in composition and at the same time produces various alterations in the rocks through which it passes.

The chemical changes produced in the rocks by percolating waters, while most active near the surface, occur also at considerable depths, and are there augmented by the internal heat of the earth. There is a lower limit to this process, however, due to the increasing density of the rocks with pressure and to the rise of temperature with increase in depth. There are good reasons for concluding that surface waters cannot descend more than twenty thousand or thirty thousand feet below the surface.

The chemical changes due to percolating water are influenced in a variety of ways by temperature. The rocks are dissolved most readily in warm, moist regions. It is in such regions also that vegetation is most luxuriant and animal life most abundant, and hence the waters are most highly charged with organic acids. Chemical action, in most instances, is retarded by cold; vegetation is less abundant and decay less rapid in cold than in warm climates; it is, therefore, in cold regions that the decay of the rocks is at a minimum.

In warm, humid countries, deep rock-decay has usually taken place, but a thick surface sheet of decomposed material is not necessarily found, as the loosened debris may be carried away as fast as it is produced. In the southern Appalachians, and in many other warm temperate or equatorial regions, the rocks are so broken and decayed, even at a depth of one hundred and fifty or two hundred feet from the surface, that they may be crumbled between the fingers or moulded like clay. In such instances the soil usually shows various tints of red and yellow, the colours being due to the oxidation and hydration of iron present in them.

In warm, dry countries chemical changes in the surface material are retarded, although the rocks may be greatly shattered by changes of temperature. In such regions the soils are seldom red.

Chemical changes produced by percolating water below the superficial portion of the earth — that is, below, perhaps, one hundred feet — increase with depth, on account of progressively increasing temperature, but these changes are beyond the immediate subject under discussion. An important agency in rock disintegration and decay having

DISINTEGRA TION AND DEC A V OF ROCKS g

its source deep within the earth, however, is manifest especially in volcanic regions where steam charged with various acids rises through fissures and other openings. During volcanic eruptions, but more particularly after a volcano has passed to the condition of a fumarole or a solfatara, heated vapour and gases charged with sulphuric, hydrochloric, carbonic, and other acids escape in large volumes, sometimes continuously for centuries, and produce conspicuous changes in the rocks through which they rise. Similar but usually less copious exhalations occur from lava streams, and produce alterations in the lava which influence the character of the soil resulting from them.

The chemical alterations produced by percolating water, and less commonly by volcanic gases, in rocks near the surface, are in part by solution, and in part oxidation, hydration, precipitation, etc. These changes, except the last mentioned, may be grouped, at least in a general way, under the term rock-decay. In decaying, the rocks are more or less disintegrated, however, since the more soluble minerals are removed, thus allowing the less soluble rock constituents to crumble and fall apart. The processes of rock-disintegration and rock-decay mutually assist each other, and progress at the same time. The result is that the surface layer of the earth's crust is profoundly altered, and a sheet of modified material is produced, which is designated in part as soil and in part as rock detritus.*

Tlie Removal and Renewal of Surface Debris. — The sur-

' The name Regolith, meaning blanket-stone, has recently been proposed for the superficial material covering the earth, by G. P. Merrill, A Treatise oh Rocks, Rock- Weathering and Soils^ 1897, p. 299.

lO RIVERS OF NORTH AMERICA

face changes just considered have been in progress since the first appearance of land, and will continue as long as continents and islands exist. In former geological periods the agencies enumerated, particularly those of a chemical nature, were more active than now, and have varied from time to time, in probably all portions of the earth's surface, with climatic and other changes. Throughout all geological ages, the streams have been actively engaged in removing the disintegrated and more or less chemically altered surface portions of the earth's crust. In places and at certain times, the debris has been removed as fast as formed, and bare, hard rock surfaces have been exposed ; at other times, the supply has been in excess of the demand, and deep accumulations have resulted. The surface sheet of debris has been continually wasting and continually renewed. Throughout the history of the earth, topographic changes have been in progress. Mountain ranges and systems have been upraised, the rocks composing them fractured and chemically altered, and borne away by streams. Where once a magnificent mountain range reared its battlements among the clouds, there is now a plain but little elevated above the sea. Not only one, but several such geographical cycles have run their courses in many lands.

During the cycles still in progress human agencies have been added to those previously in action. This new element in the earth's history has become more and more important as man has advanced in civilisation. In part, human industries have retarded the work of physical and chemical agencies, but in the main man has been a destroyer.

The removal of the portion of the earth's crust rising

DISINTEGRA TION AND DECA V OF ROCKS 1 1

above the sea, during each cycle, has been done almost wholly by streams. The manner in which the rocks are prepared for transportation, however, is quite as important to the geographer as the methods employed for their removal, but the brief review given above of this division of the general process must suffice for the present.

The student who may wish to continue the studies outlined in this chapter will find assistance in the books mentioned below. ^

^ George P. Merrill. A Treatise on Rocks, Rock- Weathering and Soils, pp. 172-398. The Macmillan Co., 1897.

Israel C. Russell. The Decay of Rocks and the Origin of the Red Colour cf Certain Formations. U. S. Geological Survey, Bulletin No. 52, 1889.

Israel C. Russell. "A Reconnoissance in South-Eastern Washington." U. S. Geological Survey, Water-Supply and Irrigation Papers, No. 4, pp. 57- 69, 1897.

George P. Marsh. The Earth as Modified by Human Action. Charles Scribner's Sons, 1885.

John C. Branner. '* Decomposition of Rocks in Brazil." Bulletin of the Geological Society of America, vol. vii., pp. 255-314, 1896.

Alexis A. Julien. "On the Geological Action of the Humus Acids," in American Association for the Advancement of Science, Proceedings, vol. xxviii., pp. 311-410, 1879.

Walter Maxwell. Lavas and Soils of the Hawaiian Islands. Honolulu, i8q8.

Chapter II Zaivs Governing The Streams

THE water which flows off from the land, as is well known, is supplied by the condensation of vapour in the air. A part of the water reaching the earth flows over the surface and gathers into rills which unite to form larger streams, and a part sinks below the surface and, after following an underground course, usually by percolation through porous soil or rocks, emerges in springs, many of which join the surface flow.

It is also well known that streams ranging in size from the smallest rills to the mightiest rivers are engaged either occasionally, as during floods, or continually, in carrying away material that was previously a portion of the land. The manner in which this material is acquired by the streams, the way it is transported, the effects it has on the flow of the streams, and on their bottoms and sides, the modifications in the configuration of the surface of the land due to the removal and re-deposition of debris, etc., are all phenomena that obey definite laws and are variously modified by conditions. If one can ascertain the laws governing the behaviour of a single stream, they should also apply not only to the streams of North America, but to those of all land areas.

i

Plate I.

Fig. a. Marion River, Adirondacks, New York.

Summer stage, showing stones which are moved during high-water. (Photograph by S. R. Stoddard.)

Fig. B. Ingall's Creek, Washington.

Showing boulders too large for the stream to move even during high-water stages.

No one stream, perhaps, in the limited time that an individual student is enabled to examine it, will furnish illustrations of all of the modifying conditions influencing the life of a great river. By selecting typical examples, however, affected by different modifying conditions, we may sketch a composite picture which will represent the various phases in the life history of a single river that has carried on its work for tens of thousands of years.

How Streams Obtain their Loads, — Rain-drops strike the earth with a certain force, dependent on their size, the distance they descend, the direction and force of the wind, etc. If rain-drops fall on the surface of a still pool we may see them rebound. If we face a rain-storm, the sting of the beating drops again assures us that they exert a considerable force on the objects against which they strike. When the drops fall on a solid rock surface, they gather in rills of clear water, but if they fall on loose soil, as a newly ploughed field, for example, the finer particles of earth are disturbed, and as the waters gather into rills and flow away in obedience to gravity, they are turbid with earth particles held in suspension. The turbid rills unite in brooks, and these again combine to form larger streams. The fine silt disturbed by the impact of the rain-drops is carried by the rills to the brooks and thence onward, perhaps with many halts, to the sea. After heavy rains even large rivers become muddy. The lakes and large areas in the sea near the mouths of rivers are then discoloured. This happens during every storm the world over, and evidently, if sufficient time be allowed, must lead to changes of great magnitude both in the topography of the land from which material is removed and in the shape of the basins where it is deposited.

When the surface of the land is dry, and especially when bare of vegetation, earth particles are moved by the wind in much the same manner that streams take up and transport the flakes and grains of rock which they are competent to transport. The dust and sand carried by the wind and falling in streams is another source from which they obtain material suitable for removal.

The fine rock powder, or glacial meal as it is termed, produced by the grinding of stones held in the ice against each other and on the rocks over which the glaciers flow, is contributed directly to the waters formed by the melting of the ice. For this reason nearly every glacier-born stream is turbid and heavy with silt.

Volcanoes during times of violent eruption discharge vast quantities of fine dust, and in many instances equally abundant rock fragments of the size of sand and gravel. When material extruded in these forms falls in streams, or is carried in by tributary rills and by the wind, another source is furnished from which streams receive their initial loads. There are yet other methods by which streams are supplied with material in a suitable condition to be transported. Among these may be noted the fall of cosmic dust, disturbances produced by avalanches and landslides, the uprooting of trees, the impact of driftwood and floating ice on the bottoms and sides of stream channels, the movement of roots and overhanging branches by the wind and by the currents of the streams themselves, disturbances of the material forming the bottoms and sides of stream channels by ani-

LAWS GOVERNING THE STREAMS I 5

mals, — as by beavers, for example, — contributions of shells and siliceous cases from organisms like mollusks and diatoms living in the waters, etc. Man promotes the transfer of solid matter to the streams in various ways, more especially by ploughing and otherwise disturbing the soil, and by the removal of forests. All of the methods mentioned in this paragraph, however, are of secondary importance in comparison with the influence of rain, wind, and glaciers.

The particles carried in suspension by streams tend to fall to the bottom, being continually pulled down by gravity, but in flowing water there are various currents, some of which tend upward and exert an influence on the falling particles in opposition to gravity. The currents in the water move the suspended particles in various directions and retard their fall to the bottom, but the resultant movement is in the direction of the flow of the stream.

The particles carried by streams fall to the bottom many times during their journeys, and rest there for a period perhaps brief but possibly long, and are again lifted by upward currents and brought within the influence of the onward flow. Material thus transported by a stream may for convenience be termed its load. Streams not only receive their initial loads in the various ways just stated, but there are other methods by which the same result is reached. As will be considered later, flowing water exerts a pressure on objects against which it strikes. If this force be great enough to move the objects in the path of a stream, they will be pushed along, rolled over, or, with the assistance of upward currents, taken in suspension. The strength of the water current determines the size of the particles it can

1 6 RIVERS OF X OR Til AMERICA

carry, so that a stream of a given velocity, but without an initial load, would be able to remove from its channel all of the loose particles it is competent to carry and thereafter would run clear unless its velocity were increased.

The principal methods by which streams receive their initial loads insure a waste of the land between the drainage lines, and consequently this land changes in topographic form. The deepening and broadening of the stream channels is accomplished principally by the friction of the debris carried through them, aided also by solution. The laws governing this complex process will be considered later.