the john muir exhibit - writings - studies_in_the_sierra - chapter 6

Studies in the Sierra

by John Muir

VI
Formation of Soils

Nature has plowed the Sierra flanks more than a mile deep through lava, slate, and granite, thus giving rise to a most lavish abundance of fruitful soils. The various methods of detachment of soil-fragments from the solid rocks have been already considered in the foregoing studies on glacial and post-glacial denudation. It now remains to study the formation of the variously eroded fragments into beds available for the uses of vegetable life.

If all the soils that now mantle the Sierra flanks were spread out in one sheet of uniform thickness, it would measure only a few feet in depth, and its entire removal would not appreciably affect the configuration of any portion of the range. The largest beds rarely exceed a hundred feet in average thickness, and a very considerable proportion of the whole surface is naked. But we have seen that glaciers alone have ground the west flank of the range into soil to a depth of more than a mile, without taking into account the work of other soil-producing agents, as rains, avalanches, torrents, earthquakes, etc. It appears, therefore, that not the one-thousandth part of the whole quantity of soil eroded from the range since the beginning of the glacial epoch is now left upon its flanks.

The cause of this comparative scantiness of the Sierra soil-beds will be readily apprehended when we reflect that the glacier, which is the chief soil-producing agent, no sooner detaches a soil-fragment than it begins to carry it away. During the long glacial winter, soil-material was poured from the range as from a fountain, borne outward by the mighty currents of the ice-sheet to be deposited in its terminal moraines. The only one of these ancient ice-sheet moraines which has retained its principal characteristics unaltered down to the present time is that magnificent belt of soil upon which all the majestic forests of the Sierra are growing. It stretches along the west flank of the range like a smooth-flowing ribbon, waving compliantly up and down over a thousand hills and hollows, at an elevation of from four to seven thousand feet above the level of the sea. In some places it is more than a hundred feet deep and twenty miles wide, but it is irregular as a sun-wasted snow-wreath both in width and in depth, on account of the configuration of the surface upon which it rests, and the varying thickness and declivity of the ice-sheet at the period of its deposition. The long weathering and the multitude of storm-washings to which it has been subjected have made its outlines still more indefinite and variable. Furthermore, its continuity is interrupted at intervals of fifteen or twenty miles by the river cañons which cross it nearly at right angles. For, at the period of the deposition of the main soil-belt as a terminal moraine of the ice-sheet, long finger-like glaciers extended down every one of these cañons, thus effectually preventing the continuance of the main terminal moraine across the cañon channels.

The method of the deposition of broad belts of terminal-moraine soil will be made plain by reference to Figure 1, which represents a deposit of this kind lying at the foot of Moraine Lake, made by the Bloody Cañon glacier in its recession toward the period of its extinction. A A are the main lateral moraines extending from the jaws of the cañon out into the Mono Plain; 1, 2, 3, 4, 5, 6 are concentric belts of terminal-moraine soil deposited by the glacier in its retreat.

These soil-belts, or furrows, are twenty or thirty yards apart. After belt number 1 was laid down, the glacier evidently withdrew at a faster rate, until a change of climate as regards heat or cold, or the occurrence of a cluster of snowier years, checked its backward motion sufficiently to afford it time to deposit belt number 2, and so on; the speed of the dying glacier's retreat being increased and diminished in rhythmic alternations of frost and thaw, sunshine and snow, all of which found beautiful and enduring expression in its ridged moraines. The promontories P P are portions of a terminal soil-belt, part of which is covered by the lake.

Similar fields of corrugated moraine matter occur farther down, marking lingering and fluctuating periods in the recession of the glacier similar to the series we have been studying. Now, it is evident that if, instead of thus dying a lingering death, the glacier had melted suddenly while it extended into the Mono plain, these wide soil-fields could not have been made. Neither could the grand soil-belt of the western flank have existed if the ice-sheet had melted in one immense thaw while it extended as a seamless mantle over all the western flank. Fortunately for Sierra vegetation and the life dependent upon it, this was not the case; instead of disappearing suddenly, like a sun-stricken cloud, it withdrew from the base of the great soil-belt upward, in that magnificently deliberate way so characteristic of nature--adding belt to belt in beautiful order over lofty plateaus and rolling hills and valleys, wherever soil could be made to lie.

Fig. 1

Winds and rains, acting throughout the ample centuries, smooth rough glacial soils like harrows and rollers. But this culture is carried on at an infinitely slow rate, as we measure time. Comparing the several moraine-fields of Bloody Cañon, we observe that the ridged concentric structure (Fig. 1) becomes gradually less distinct the farther we proceed out into the plain, just as the plow-ridges in a farmer's field become less distinct the more they are harrowed. Now, the difference in time between the deposition of contiguous moraine-fields in Bloody Cañon is probably thousands of years, yet the difference as regards smoothness and freshness of aspect corresponding to this difference in time is in some instances scarcely discernible. In the field represented in Figure 1 these leveling operations may be studied to excellent advantage. The furrows between the several ridges are leisurely filled up by the inblowing and washing of leaves and the finer material of the adjacent ridges. As the weathering of the surface boulders goes on, the crumbling material which falls from them collects about their bases, thus tending to bury them, and produce that smoothness of surface which characterizes all the more ancient moraine-fields of the Sierra. The great forest soil-belt of the west flank has not been hitherto recognized as a moraine at all, because not only is it so immensely extended that general views of it can not be easily obtained, but it has been weathered until the greater portion of its surface presents as smooth an appearance as a farmer's wheat-field.

It may be urged against the morainal origin of the forest belt that its sections exposed by freshet streams present a quite different appearance from similar sections of more recent moraine-beds unmistakably such; but careful inspection shows the same gradual transition from the boulder roughness of the one to the crumbled earthiness of the other that we have already traced between the superficial roughness and smoothness of moraines according to age.

Fig. 2

Under certain conditions moraine boulders decompose more rapidly beneath than upon the surface. Almost every section of the forest belt presents specimens in every stage of decay, and, because those that are water-rounded and polished are more enduring than others, they occur in comparatively greater abundance as the soil becomes more ancient. The position of the soil-belt is given in the ideal cross-section of the range (Fig. 2). Its upper limit nearly coincides with the edge of a comparatively level bench, A B, extending back to the summit peaks. Upon this lofty, gently inclined bed the waning ice-sheet lay nearly motionless, shallowing simultaneously across its whole breadth, and finally broke up into distinct ice-streams which occupied the present river cañons. These have left their lateral moraines in the form of long branching ridges of soil, several miles apart, extending from the summit ice-wombs down to the main soil-belt, into which they blend and disappear. But if the ice-sheet had maintained its continuity to the very end of the glacial epoch, soil would evidently have been laid down in one continuous bed all the way back to the summit, because under these conditions every portion of the surface in succession would have been loaded with terminal moraine-belts pressed one against the other like plow-ridges. Under the conditions which prevailed toward the close of the great winter, the separate glaciers as well as the ice-sheet shallowed, became torpid, and died away simultaneously throughout all this upper region; no terminal moraine; are therefore to be met until we reach those of the small residual glaciers which took shelter in the loftiest and coolest shadows of the summit peaks. Nor will this state of things be wondered at, when we consider how slight is the difference in elevation, and consequently in climate, between the upper and lower limits (A and B. Fig. 2) of this bare alpine bench, as compared with that of the slope (C A) beneath it, upon which the soil-belt lies.

The effect of shadows in determining the formation, size, and distribution of glacial soil-beds must not be overlooked. When the seasons grew warm and the long crooked glaciers were driven from the sun-beaten summit bench, thousands of small residual glaciers, from half a mile to two or three miles in length, lingered on through many a century in the shelter of frosty shadows. Accordingly, we find the moraines of these hiding glaciers in the highest and coolest recesses, shaped and measured with strict reference to their adjacent shadows. A considerable number of these interesting shadow-moraines are still in process of formation, presenting a raw and rubbish-like appearance, as if the boulders, mud, and sand of which they are composed had been newly mined from the mountain's flank, and dumped loosely from a car. Ancient shadow-moraines, delightfully gardened and forested, occur in all deep Yosemitic cañons trending in an east and west direction; but their first forms are so heavily obscured by thousands of years of weathering that their shadow-glacial origin would scarcely be suspected.

In addition to these broad zones and fields and regularly deposited moraine ridges, glacial soil occurs in isolated strips and patches upon the wildest and most unlikely places-aloft on jutting crags, and along narrow horizontal benches ranged one above another, on sheer-fronted precipices, wherever the strong and gentle glaciers could get a boulder to lie. To these inaccessible soil-beds companies of pines and alp-loving flowers have found their way, and formed themselves into waving fringes and rosettes, whose beauty is strikingly relieved upon the massive ice-sculptured walls.

Nothing in the history of glacial soil-beds seems more remarkable than their durability in the forms in which they were first laid down. The wild violence of mountain storms would lead one to fancy that every moraine would be swept from plateau and ridge in less than a dozen seasons, yet we find those of the upper half of the range scarcely altered by the tear and wear of thousands of years. Those of the lower half are far more ancient, and their material has evidently been shifted and re-formed until their original characteristics are almost entirely lost.

These fresh glacier-formed soils are subject to modifications of various kinds. After the coarse, unbolted moraine soils derived from granite, slate, and lava have been well watered and snow-pressed, they are admirably adapted for the ordinary food and anchorage of coniferous trees, but further manipulation is required to fit them for special grove and garden purposes. The first and most general action to which they are subjected is that of slow atmospheric decomposition, which mellows and smooths them for the reception of blooming robes of under-shrubs and grasses, and up to a certain point augments their capacity for the support of pines and firs. Streams of rain and melting snow rank next in importance as modifiers of glacial soils. Powerful torrents waste and change the most compact beds with great rapidity, but the work done by small rain-currents and low-voiced brooks is very much less than is vaguely supposed. The brook which drains the south flank of the Clouds' Rest ridge, above Yosemite Valley, in making its way southward to join the Nevada Creek, is deflected to the west by the right lateral moraine of the ancient Nevada glacier, and compelled to creep and feel its way along the outside of the moraine as far as to where it is caught between the moraine and an escarpment which advances from the Clouds' Rest crest. When halted here, it spread into a pool, and rose until it was able to effect its escape over the lowest portion of the barrier. Now, this stream, which in ordinary stages is about five feet wide and a foot deep, seems to have flowed unfailingly in one channel throughout all the long post-glacial centuries, but the only erosion the moraine has suffered is the removal of sand, mud, and some of the smaller boulders, while the large stones, jammed into a kind of wall, are merely polished by the friction of the stream, and bid fair to last tens of thousands of years. The permanence of soils depends more upon their position and mechanical structure than upon their composition. Coarse porous moraine matter permits rains and melting snows to percolate unimpeded, while muddy and impermeable beds are washed and wasted on the surface.

Snow avalanches more resemble glaciers in their methods of soil formation and distribution than any other of the post-glacial agents. The century avalanche sweeps down all the trees that chance to stand in its path, together with soils of every kind, mixing all together without reference to the size of their component fragments. Most of the uprooted trees are deposited in lateral windrows, heads downward, piled upon each other, and tucked snugly in alongside the clearing; while a few are carried down into the valley on the snout of the avalanche, and deposited with stones, leaves, and burs, in a kind of terminal moraine.

The soil accumulations of annual avalanches are still more moraines like in form, and frequently attain a depth of from forty to fifty feet. They are composed of mud, sand, coarse granules, and rough angular blocks, avalanched from the mountain side, and sometimes water-washed pebbles also, derived from the channels of streams.

Fig. 3.

Thus, the largest of the Clouds' Rest avalanches, in rushing down their magnificent pathway of nearly a mile in vertical depth, on their arrival at the Tenaya Creek (Fig. 3) dash across its channel and up the opposite bank to a height of more than a hundred feet, pushing all the pebbles and boulders of the stream up with them. Spring freshets bring down a fresh supply of pebbles and boulders from year to year, which the avalanches patiently add to their moraine, until in a few thousand years these washed pebbles form a considerable proportion of the mass. Trees over a hundred years old occur upon the upper portions of some of these avalanche-beds, showing that no avalanche of sufficient power to disturb them had occurred since they began to grow. The lower portions of these beds are, on the contrary, in a raw formative condition, and about as plantless as the shining boulder-beds in the bottoms of rivers.

Again, stone avalanches have their share in depositing soil. The observer among beetling Yosemitic cliffs occasionally sees a single boulder eight or ten feet in diameter whizzing down the sky like a comet with a tail of dust two thousand feet long. When these huge soil-grains strike among other boulders at the end of their course, they make a sound deeper and heavier than thunder; the ground trembles, and stone-spray is whirled and spattered like water-spray at the foot of a fall.

The crushed and pounded soil-beds to which avalanches of this kind give rise seem excellently well adapted to the growth of forest trees, but few of them are sufficiently matured to be available, and the trees that venture upon them are in constant danger of their lives. These unplanted beds occur most commonly at the base of cliffs intersected by feldspathic veins, the decomposition of which causes the downfall of additional material from year to year. On the contrary, the rougher and far more important soil-beds resulting from earthquake avalanches are formed almost instantaneously, without being subsequently augmented in any appreciable degree for centuries. The trees, therefore, and various shrubs and flowers which find them tolerable or congenial dwelling-places soon take possession of them, and soothe their rugged features with a mantle of waving verdure.

At first thought no one would suppose that in a tumultuous pellmell down-crash of rifted rocks any specialization could be accomplished in their deposition. Both the suddenness and the violence of the action would seem to preclude the possibility of the formation of any deposit more orderly than a battered rubbish-heap. Every atom, however, whether of the slow glacier or swift avalanche, is inspired and directed by law. The larger blocks, because they are heavier in proportion to the amount of surface they present to the impeding air, bound out farther; and, because obstructions of surface irregularities have less effect upon larger blocks, they also roll farther on the bottom of the valley. The small granules and sand-grains slip and roll close to the cliff, and come to rest on the top of the talus, while the main mass of the talus is perfectly graduated between these extremes. Besides this graduation accomplished in a vertical and forward direction, beautiful sections are frequently made in a horizontal and lateral direction, as illustrated in Figure 4. A B is a kind of natural trough or spout near the base of the cliff, directed obliquely downward, into which a portion of the avalanche-stream, F. falls, and is spouted to the left of its original course. Because the larger boulders composing the spouted portion of the current move faster, their momentum carries them farther toward H. giving rise to the talus E, while the finer material is deposited at D. Again, the blocks sufficiently large to bound out beyond the deflecting spout from the rough talus C, while the smallest fragments of all--namely, the fine dust derived from chafing--float out far beyond, and settle in thin films silently as dew.

Fig. 4

Fig. 5

In portions of cañon walls where diagonal cleavage is developed, inclines such as A B (Fig. 5) are common. If two boulders in falling from the heights above should strike glancingly at A, the greater mass or more favorable form of boulder B might cause it to bound sufficiently far to reach the second incline, which would carry it toward D; while the smaller boulder, C, falling short, might fall under the guidance of a third incline, and be shed off toward E, the two boulders finally coming to rest a hundred yards or more apart. By these means the most delicate decompositions of stone-torrents are effected, the various resulting soils being delivered at different shoots and spouts, like the bran, shorts, and fine flour of a gristmill. The ages of the oldest trees growing upon these soils furnish data by which some approximation to the time of their formation may be made.

The first post-glacial earthquake sufficiently severe to produce large avalanches occurred at least three centuries ago, and no other of equal power has occurred since. By this earthquake alone, thousands of acres of noble soil-beds were suddenly and simultaneously deposited throughout all the deep cañons of the range. Though thus hurled into existence at a single effort, they are the most changeless and indestructible soil formations in the Sierra. Excepting those which were launched directly into the channels of rivers, scarcely one of their wedged and locked boulders has been moved since the day of their creation. In striking contrast with these terrible demonstrations of mechanical energy, made the deposition of earthquake soils, is the silent and motionless transformation of solid granite into loose fine soil-beds by oozing water and the tranquil play of the atmosphere. Beds eight or ten feet deep occur on Mounts Watkins and El Capitan, on the edge of the Yosemite Valley, where the decomposition had been effected so calmly that the physical structure presents no conspicuous change; the quartz, mica, and horn-blende retaining the same relative positions as when solid, yet so perfectly disintegrated that, like sand, it may be cut into with a spade. But these unmoved beds created on the spot are of relatively small extent, and as yet play an insignificant part in the support of Sierra vegetation. The main body of the smaller soil-fragments, weathered loose by the atmosphere, are transported and redeposited by winds and rains. Magnificent wind-rivers sweep the high Sierra, carrying large quantities of sand, dust, and mica flakes, besides larger fragments in the form of rough grains. These are distributed in smooth undulating fields and patches, adapted to the wants of the dwarf Pinus albicaulis and many of the most precious of Sierra shrubs and flowers. Many of the smaller alpine wind-beds are exceedingly beautiful nestling in the lee of rough beaten rocks, their edges waved and embroidered, and their surfaces delicately dinted and ruffled like the garden-plats of children. During the post-glacial eruptions of the volcanoes of the Mono basin, winds distributed showers of cinders and ashes upon all the soil-beds of the adjacent Sierra. Hundreds of square miles of area are thus sprinkled on the upper basins of the San Joaquin, Merced, and Tuolumne rivers; the copiousness of the cinder-showers increasing the nearer the Mono volcanoes are approached as a center.

The numerous domes and castellated rocks distributed over the ridges and divides of the middle region abound in garnet, tourmaline, quartz, mica, and feldspar crystals, which, as the mass of the rocks decompose, are set free and fall in minute avalanches, and gradually accumulate until they come to form belts of crystalline soil. In some instances, the various crystals occur only here and there, sprinkled in the gray gravel like daisies in a sod; but in others, half or more of the encircling talus seems to be made up of crystals, tilted at all angles, and laid open to the sun. And whether in the mild flush of morning or evening, or in the dazzling white of high noon, they manifest themselves as the most exquisitely beautiful of all the soil-beds in the range.

In the hollows and levels we find soil-beds that have been compounded and laid down by streams of water. But these may be regarded as little more than reformations of glacial deposits; for the quantity of soil material eroded from solid rock by post-glacial agents is as yet hardly appreciable. Water-beds present a wide range of variability both in size and structure. Some of the smallest, each sustaining a tuft or two of grass, have scarcely a larger area than the flower-plats of gardens; while others are miles in extent, and support luxuriant groves of pine trees two hundred feet in height. Some are composed of mud and sand-grains, others of ponderous boulders, according to the power of the depositing current and the character of the material that chanced to lie in its way.

Glaciers are admirably calculated for the general distribution of soils in consequence of their rigidity and independence of minor inequalities of surface. Streams of water, on the contrary, are fitted only for special work. Glaciers give soil to high and low places almost alike; water-currents are dispensers of special blessings, constantly tending to make the ridges poorer and the valleys richer. Glaciers mingle all kinds of materials together, mud particles and rock blocks a hundred feet in diameter; water, whether in oozing currents or passionate torrents, constantly discriminates both with regard to size and shape of material, and acts as a series of sieves for its separation and transportation.

Glacial mud is the finest mountain meal ground for any purpose, and its transportation into the still water of lakes, where it is deposited in layers of clay, was the first work that the young post-glacial streams of the Sierra were called upon to do. Upon the clay-beds thus created avalanches frequently pile tangled masses of tree-trunks, mingled with burs and leaves and rocky detritus scraped from the mountain side. Other layers of mud are deposited in turn, together with freshet-washings of sand and gravel. This goes on for centuries from season to season, until at length the basin is filled and gradually becomes drier. At first, the soil is fit only for sedges and willows, then for grasses and pine-trees. This, with minor local modifications, is the mode of creation of the so-called flat and meadow soil so abundantly distributed over all parts of the range.

Genuine bogs in this period of Sierra history occur only in shallow alpine basins, where the climate is sufficiently cool for the growth of sphagnum, and where the surrounding topographical conditions are such that they are safe, even in the most copious rains and thaws, from the action of flood-currents capable of carrying stones and sand, but where the water supply is nevertheless sufficiently constant and abundant for the growth of sphagnum and a few other plants equally fond of cold water. These dying from year to year--ever dying beneath and living above--gradually give rise to those rich spongy peat-soils that are the grateful abodes of so many of the most delightful of alpine plants.

Beds of sloping bog-soil, that seem to hang like ribbons on cool mountain sides, are originated by the fall of trees in the paths of small creeks and rills, in the same climates with level bogs. The interlaced trunks and branches obstruct the feeble streams and dissipate them into oozing webs and stagnant pools. Sphagnum speedily discovers and takes possession of them, absorbing every pool and driblet into its spongy stems, and at length covers the muddy ground and every log and branch with its rich rounded bosses.

Here the attentive observer is sure to ask the question, Are the fallen trees more abundant in bogs than elsewhere in the surrounding forest?--and if so, then, why? We do find the fallen trees in far greater abundance in sloping bogs, and the cause is clearly explained by young illustrative bogs in process of formation. In the first place, a few chance trees decay and fall in such a manner as to dam the stream and flood the roots of other trees. Every tree so flooded dies, decays, and falls. Thus, the so-called chance-falling of a few causes the fall of many, which form a network, in the meshes of which the entangled moisture is distributed with a considerable degree of uniformity, causing the resulting bog to be evenly inclined, instead of being cast into a succession of irregular terraces, one for each damming log.

Black flat meadow deposits, largely composed of humus, are formed in lake basins that have reached the last stage of filling up. The black vegetable matter is derived from rushes and sedges decaying in shallow water for long periods. It is not essential that these beds be constantly covered with water during their deposition, but only that they be subject to frequent inundations and remain sufficiently moist through the driest seasons for the growth of sedges. They must, moreover, be exempt from the action of overflowing flood-currents strong enough to move gravel and sand. But no matter how advantageous may be the situation of these humus beds, their edges are incessantly encroached upon, making their final burial beneath drier mineral formations inevitable. This obliterating action Is going on at an accelerated rate on account of the increasing quantity of transportable material rain-streams find in their way. For thousands of years subsequent to the close of the ice-winter, a large proportion of the Sierra presented a bare, polished surface, and the streams that flowed over it came down into the meadows about as empty-handed as if their courses had lain over clean glass. But when at length the glacial hard-finish was weathered off, disintegration went on at a greatly accelerated speed, and every stream found all the carrying work it could do.

Bogs die also, in accordance with beautiful laws. Their lower limit constantly rises as the range grows older. The snow-line is not a more trustworthy exponent of climate than the bog-line is of the age of the regions where it occurs, dating from the end of the ice epoch.

Besides bogs, meadows, and sandy flats, water constructs soil-beds with washed pebbles, cobblestones, and large boulders. The former class of beds are made deliberately by tranquil currents; the latter by freshets, caused by the melting of the winter snow, severe rain-storms, and by floods of exceptional power, produced by rare combinations of causes, which in the Sierra occur only once in hundreds of years. So vast is the difference between the transporting power of rivers in their ordinary every-day condition and the same rivers in loud-booming flood, that no definite gradation exists between their level silt-beds and rugged boulder deltas. The ordinary power of Sierra streams to transport the material of boulder soils is very much overestimated. Throughout the greater portion of their channels they can not, in ordinary stages of water, move pebbles with which a child might play; while in the sublime energy of flood they toss forward boulders tons in weight without any apparent effort. The roughly imbricated flood-beds so commonly found at the mouths of narrow gorges and valleys are the highest expressions of torrential energy with which I am acquainted. At some time before the occurrence of the grand soil-producing earthquake, thousands of magnificent boulder-beds were simultaneously hurried into existence by one noble flood. These ancient boulder and cobble beds are distributed throughout the deep valleys and basins of the range between latitude 39° and 36° 30'; how much farther I am unable to say. They are now mostly overgrown with groves of oak and pine, and have as yet suffered very little change. Their distinguishing characteristics are, therefore, easily readable, and show that the sublime outburst of mechanical energy developed in their creation was rivaled only in the instantaneous deposition of the grand earthquake beds.

Notwithstanding the many august implements employed as modifiers and reformers of soils, the glacier is the only great producer. Had the ice-sheet melted suddenly, leaving the flanks of the Sierra soilless, her far-famed forests would have had no existence. Numerous groves and thickets would undoubtedly have established themselves on lake and avalanche beds, and many a fair flower and shrub would have found food and a dwelling-place in weathered nooks and crevices. Yet the range, as a whole, would seem comparatively naked. The tattered alpine fringe of the Sierra forest, composed of Pinus flexilis and P. aristate, oftentimes ascends stormy mountain flanks above the upper limit of moraines, upon lean, crumbling rock; but when they have the opportunity, these little alpine pines show that they know well the difference between rich, mealy moraines and their ordinary meager fare. The yellow pine is also a hardy rock-climber, and can live on wind and snow, but it assembles in forests and attains noble dimensions only upon nutritious moraines; while the sugar pine and the two silver firs, which form so important a part of the grand forest belt, can scarcely maintain life upon bald rocks in any form, and reach full development only in the best moraine beds, no matter what the elevation may be. The mass of the Sierra forests indicates the extent and position of the moraine-beds far more accurately than it does lines of climate. No matter how advantageous the conditions of temperature and moisture, forests can not exist without soil, and Sierra soils have been laid down upon the solid rock. Accordingly, we find luxuriant forests two hundred feet high terminated abruptly by bald glacier-polished pavements.

Man also is dependent upon the bounty of the ice for the broad fields of fertile soil upon which his wheat and apples grow. The wide plains extending along the base of the range on both sides are mostly reformations of morainal detritus variously sorted and intermixed. The valleys of the Owens, Walker, and Carson rivers have younger soils than those of the Sacramento and San Joaquin--that is, those of the former valleys are of more recent origin, and are less changed by post-glacial washings and decomposition. All the soil-beds remaining upon the Sierra flanks, when comprehended in one view, appear like clouds in a sky half-clear; the main belt extending along the middle, with long branching mountains above it, a web of washed patches beneath, and with specialized meadow and garden flecks everywhere.

When, after the melting of the winter snow, we walk the dry channel of a stream that we love, its beds of pebbles, dams of boulders, its pool-basins and potholes and cascade inclines, suggest all its familiar forms and voices, as if it were present in the full gush of spring. In like manner the various Sierra soil-beds vividly bring before the mind the noble implements employed by nature in their creation. The meadow recalls the still lake, the boulder delta, the gray booming torrent, the rugged talus, the majestic avalanche, and the moraine reveals the mighty glaciers silently spreading soil upon a thousand mountains. Nor in all these involved operations may we detect the faintest note of disorder; every soil-atom seems to yield enthusiastic obedience to law-boulders and mud-grains moving to music as harmoniously as the far-whirling planets.

---

[ Back to Chapter 5 | Forward to Chapter 7 | Table of Contents ]