THE SOILS OF CENTRAL AMERICA AND NORTHERN SOUTH AMERICA.

By Hugh H. Bennett, Bureau of Soils,U. S. Department of Agriculture.

The soils of the humid regions of Central America and of northernSouth America generally are markedly unlike those of the humid parts ofthe United States. There are exceptions that will be referred to; butover large areas in most of the tropical regions investigated soilproperties were encountered which were astounding to one who had seenbut little of these countries. Some of the most outstanding character-istics are the intense degree of soil friability; great depth ofweathering; strong resistance to erosion; scarcity of leaf mold indense forests, where the soils have a good content of organic matter;and land of excellent productivity, where the rainfall ranges fromaround 100 to over 200 inches annually. In many places there is nosharp horizonal development; in other places the horizons are distinct.

One »f the first areas examined in Costa Rica was the pineapplefarm of the United Fruit Company at Columbiana. 'Here a soil wasfound in which it was impossible tt detect a single grain of sand -a soil largely of a colloidal nature with only .7 of one per cent ofparticles coarser than silt. It was raining at the time this areawas entered, it had been raining for weeks, in fact, it rains in thelocality throughout the year, the total precipitation amounting tomore than 150 inches, At the time freshly cleared land was beingplowed with a disk to a depth of about 7 inches. In spite of themoisture the soil was turning up in a decidedly crumbly condition,and but little of it stuck to the shoes, as one walked across theplowed ground. This state of affairs was not in keeping with theproperties of any soil previously seen, except sandy soils. Ineastern United States a soil approximating such a fine texturewould have been, under similar conditions of moisture, so stickythat a paddle would have been needed to relieve the feet of theirloads of mud.

Below 5 feet, 5 inches the content of material finer thansilt amounted to 90.5 per cent, yet that too had the character ofa. mellow loam,

Here most of the rainfall enters the ground, the runoff fromthe smoother lands being negligible* The original growth is heavytropical forest. Much of the land had been cleared and planted tobananas more than 30 years previously, and good crops were takenoff continuously lor something like 20 years, without fertilization,or cultivation. The dreaded Panama disease came, and the fieldswere abandoned or planted to cacao. An almost impenetrable junglesprang up immediately over the unused lands. Recently, portionsof this have been recleared, and fine yields of pineapples are

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being obtained, There were also citrus and a variety of tropicalfruits, and patches of corn and sugar cane. All crops were doing well.There was evidence of excellent and durable productivity. Chemicalanalysis showed the following composition:

CHEMICAL ANALYSES OF COLUMBIANA CLAY1 FROM COSTA RICA,2

Chemicalanalysis

SiO2

TiO2

Fe2O3

Al2O3

MnO

CaO

MgO

K2O

Na2O

P2O5

SO3Ignition loss

Total

N

CO2 fromcarbonates

Organic matter

H2O at 110°

0 to 24 inches30584

24 to 65 inches30585

65 inches30586

none none none

1. From cut on Columbiana pineapple farm.2. analyses by Edgington, G. and Holmes, R, S., in laboratory of

Bureau of Soils.

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Date _April _29,. _ _1924,

This Columbiana soil does not scour well over the mouldboard,adhering probably by force of impact rather than as the result ofstickiness. In this respect it behaves like the "push land" or redclay loam derived from basic igneous rocks of the southern Piedmont.The latter, however, is much more sticky when wet, and is higher insilica.

The Columbiana clay type occurs on a gently sloping plain nearthe base of a high mountain range, at an elevation of about 1,000feet. Its parent material consists of old outwash from the neigh-boring volcanic range, locally it is called "chocolate" land and"red" land by Americans and "tierra bermejo" by the natives, by reasonof its chocolate brown to brownish red color. Its Ph value is 5.9in the surface section, and 5 below 2 feet.

Ascending to an elevation of about 2,500 feet on the southerlyslope of the same range, near the town of Turrialba, named for thegreat volcano in that vicinity, another highly friable type wasfound, one in which weathering had proceeded to such depths thatthe rocks were well decomposed in -places to more than 100 feet,as shown in the cuts of the Limon-San Jose Railroad. A sample col-lected here to a depth of 17 feet was highly friable all the waydown, and the material beneath crushed easily between the fingers,

The principal results of chemical analysis are as follows:

Analysis of Soil from near Turrialba, Costa Rica,

Section

Inches

0 to 40

40 to 144

144 to 162

162 to 202

at 37ft.

SiO2 Fe2O3 Al2O3CaO, MgOK2O, Na2O P2O5

Organicmatter Colloids

1. Analysis by Edgington, G, and Holmes, R. S., in laboratory,of Bureau of Soils.

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The results shown in the first two sections are averages of threesubsections. In. the topmost horizon the organic matter was 7.2, andthe nitrogen .26. The highest content of sand or material coarserthan silt was 4 per cent in the section between 162 and 202 inches.The material at 37 feet had the appearance of rotten rock, yet itcontained no perceptible hard grains.

Summarizing the results down to 17 feet, there is a decrease ofsilica from 30 to 5 per cent, an increase of Fe2O3 from 13 to 19per cant, and an increase of Al2O3 from 34 to 47 per cent. Thereare no carbonates, the organic matter decreases from 7 per cent to.4 per cent, and the nitrogen froia .26 per cent to nothing; whilethe P2O5 increases from .27 to .54 per cent. The bases - lime,magnesia, potash, and eoda - are low throughout, with slightlydiminishing amounts downward. Some horizons contain only tracesof lime, and the highest amount of potash in any section is .25 inthe second and the lowest .05 in the bottom horizon.

The decomposed parent rock material at 37 feet contains 49 percent of silica as against a maximum of 30 per cent in the top soil,but only 7 per cent of Fe2O3 against a minimum of 13 and a maximumof 19 per cent in the overlying horizons, and 28 per cent of A12O3against a minimum of 34 and a maximum of 47 in the overlying layers.The amount of bases in this lower material is 9 times as groat as inany of the layers above. Phosphorous is about the same as in thelower horizons*

The proximity of layers of such divergent composition is notunusual in the tropics. Maxwell in his work on Hawaiian soils statesthat soils were found containing a high per cent of iron and a fairamount of silica separated from soils composed almost wholly ofalumina by "acute lines of division".

The indications are that this soil at Turrialba has lain inplace a very long time. Almost no erosion is taking place, andthe greater part of the heavy rainfall finds its way downward bypercolation. The temperature is never cold, nor does it ever gohigher than about 90° F, Under these conditions, latterizationapparently is taking place. The section between 162 and 202 inchesseems to represent a close approximation of latterite in the sensethat the silica has almost disappeared, the content of bases is low,and that of iron high, while alumina constitutes nearly half of thecomposition of the soil. The material is greenish and whitish incolor and its pH value is 4.9. Shaken in water, the particles fallout of suspension rapidly, leaving a perfectly clear liquid withinan hour or less.

In the western part of the range the soils are derived largelyfrom volcanic ash. Here the rainfall is lower, about 60 to 80inches, and the soils are usually much darker. These darker ash

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types are much higher in silica and bases, lower in alumina and iron,and do not show much change in the content of silica nor anything likethe increase of iron and alumina with increasing depth that character-izes the soils farther east in a more humid climate. These may be young-er soils. They are highly friable to great depths and are so resistantto erosion that the farm ditches through vrtiich water has flown swiftlyfor many years show no signs of scouring beds. Very little or nogullying has taken place in fields which have been cultivated since thetime of Spanish occupation, and probably long before this by the Indians.

They are productive soils, extensively used for co f f ee , corn,beans, potatoes, sugar cane, vegetables, and grass. Better yields areobtained than from the reddish uplands of the Turrialba district. Theyare high in organic matter and colloids. Analysis shows an increasein silica from 4-2 per cent, approximately, in the surface soil to 47per cent at 38 to 92 inches, then a drop to 40 per cent and a riseto 42 per cent between 102 and 150 inches, Iron increases graduallyfrom 10 per cent in the top layer to 14 per cent in the bottom; andthe alumina from 21 to 27 per cent. The amounts of lime, magnesia,potash, and soda are approximately 4 per cent, 2.5; .7, and 1.4,respectively, in the top layer and 1, 3, .4, and .4 per cent inthe lowest section. The colloids range from 63 per cent in the surface,to 92 per cent in the lowest horizon. This is the dominant soil overlarge areas of the Costa Rican highlands. The sample just describedwas taken at an elevation of 5,800 feet. According to mechanicalanalysis its texture is that of a clay. .Its natural consistency,however, is that of a mellow loam. Even the lowest section fromwhich a sample was taken, that from 8j to 13 feet, is exceedinglycrumbly,

Essentially the same type of soil extends down the northerlyslope of the Cordillera to an elevation of about 3,000 feet.

Leaving the highlands the low country of the great San JuanPlain was entered, and it was here in the bed of the San Carlos Riverthat the first recognizable grain of quartz said was seen during aperiod of two weeks field work in the highlands. The recent alluvialsoils of this region and of most the streams of humid Central Americaresemble closely the brown alluvium coming from the crystalline rocksof the northern Piedmont in the United States. They will not befurther referred to.

There are thousands of irregularly distributed hills over theSan Juan Plain and its extension into Nicaragua to and beyond Slue-fields. These seldom stand higher than 300 feet above the low inter-vening plain; many of them are mere hillocks. In Costa Rica andprobably also in many instances in southeastern Nicaragua a large

1. Analysis by Hough, G. J., in laboratory, Bureau of Soils.

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number of these hills are covered by red clay of moderate friability,which passes at depths of about 3 to 5 feet into soft material re-sembling decomposed reck, of splotched yellow, red, and bluish graycolors, extending to undetermined depths - more than 20 feet in manyplaces* The basal and presumably parent rock is diorite in manyplaces. The upper 3 or 4 feet of soil resembles somewhat the Davidsonclay of the southern Piedmont, but it is frequently of a slightlyacid nature and contains much more fine material - less than 7 percent of sands and more than 65 per cent of colloids. The parent rockhas weathered to greater depths than that of the Davidson soil of theUnited States, which is a red clay soil derived from diorite. Defi-nite horizons are wanting here.

These hills are densely forested, yet leaf mold is seldom seen.Usually a few leaves are scattered about over the bare clay, onlythose which have recently fallen. This is the prevailing conditionover the clay soils of the uplands of both Central .America and north-ern South America, except in occasional protected and moist situa-tions. Samples of this bare forested soil, nevertheless, contain atleast a fair supply of organic matter, often more than 5 per cent.

The predominant hill soil seen in the coastal lowlands of south-eastern Nicaragua is a duplicate of the Susquehanna clay of south-eastern United States in its mottled subsoil color, and plasticsticky character. This exists under the same conditions of heavyrainfall and warm temperature as the dioritic clay of the San-JuanPlain. It is underlain by dark colored basic recks - diabase inthe case of the samples identified. Some light colored and red,very tough siliceous cobbles are embedded in the heavy clay ofthis locality. These may have contributed some of the silica presentin the soil. Weathering has taken place to depths of 30 feet or more*

iAnalysis shows in the Blue fields a sand' content ranging from 8

per cent in the soil to 1.2 per cent in the material below 40 inches,and colloids ranging from 55 per cent in the soil to 82 per cent inthe section between 8 and 40 inches. Silica runs high, but dimin-ishes in the lower horizons. It is 59 per cent, approximately, inthe soil and 49 per cent between 3 and 10 feet. In the top soilthe content of iron is 7 per cent and of alumina 15 per cent; below40 inches the amounts have doubled in case of the iron and increasedto 24 per cent in the case of alumina» The bases are low from thesurface down - 1.5 per cent in the upper part, and 2 per cent inthe lower part* Phosphorous also is very low»

This mottled, plastic Bluefields clay is appraised locally asbeing a very poor soil; but in the same region a highly productiveclay type was found - one having very different physical and chem-ical properties. The latter soil was found on flattish, relatively

•

1. Analysis by Hough, G. J., in laboratory, Bureau of Soils,

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low country near the southern end of Pearl Lagoon. It contains 5.5per cent of sand and 80 per cent of colloids in the soil, and 5 percent of sand and 88 per cent of colloids in the subsoil. It is areddish brown, very friable clay, showing no apparent change as fardown as examined, that is, to 5 feet. Silica ranges from 30 percent in the soil to 32 per cent in the subsoil, iron from 17 to 20per cent, and alumina from 25 to 28 per cent. The content of P2O5is .5 per cent in both soil and subsoil, and there is no importantdifference in the content of the bases, lime and potash amounting toabout .3 per cent each.

Before discussing other soils, it might be well to analyzebriefly some of the characteristics of the types already described.

These types are representative of or are very similar to othersfound as far south as the western range of the Andes in westernColombia!

1. The extremely friable character of the deeply weatheredsoils, such as those of the Costa Rican highlands, appears to bedue in a very considerable degree to the character of the colloids.The colloids probably resemble somewhat those found in certain south-ern soils of the United States, as Cecil and Davidson. Colloidalmaterial extracted from a latteric horizon of the deep sample fromTurrialba, is very friable, and requires long rubbing to effectdispersion in water, and it settles out rapidly. It is of an acidnature. This friableness does not appear in all cases to be asso-ciated with the degree of hydration, as has been suggested. SampleNo, 30,572, the f i f th horizon of the Aragon clay from Turrialba,for example, contains 17.5 per cent of combined moisture, yet thematerial is as friable as moist corn meal. The moisture must becombined chiefly with the colloids, since the sample contains 87per cent of colloids.

There appears to be no special cause why the colloids hereshould be of an anhydrous character, in as much as rains are almostconstantly falling, and the temperature, while never low, is neververy high.

2. Most of the very friable soils of these regions are low insilica and high in iron and alumina. They are also frequently, butnot always, low in bases. Those types derived from volcanic ash arehigher in silica than those from basalt and diorite, although thesamples of ash soils were taken from less humid, and higher, coolerlocalities. Within the ash belt some soils were seen in whichsilica apparently was disappearing at a more rapid rate thanalumina, and latterization was taking place.

There are highly quartzose soils in these tropical regionssuch as the very sandy savanas of northeastern Nicaragua, and these

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of course are high in silica and friable owing to their coarse texture.

3. Deep seated disintegration of the parent soil material appearsto be generally associated with high friability, and reduced amountsof silica, and bases. Diminution of silica and the bases, however, isnot a universal corollary of deep disintegration, even where the climateatd lithologic conditions are not markedly different from those placeswhere severe leaching apparently has taken place, The Uruca soils ofCordillera Central in Costa Rica, for example, have weathered inplaces to more than 50 feet, and yet samples show'4 per cent of lime,and 1*4 per cent of soda in the surface foot; 3 and 1 per cent, res-pectively, between 12 and 28 inches; 1.8 and .1 per cent between 28and 38 inches; 1.6 and .6 between 92 and 102 inches; and 1.1 and .4per cent between 9 and 13 feet, along with considerable magnesia anda good content of potash from the surface section downward, theupper sections actually containing more of these bases than the deepersections* The soil of this sample is derived froa volcanic ash undera rainfall of 60 to 80 inches, most of which sinks into the ground.

4. Resistance to erosion seemingly is due in a very large degreeto high content of colloids characterized by the property of stickingto themselves, that is, not defloculating so as to fill the groundpore space with firm material. If there were considerably largeramounts of silt and fine sand in the soils it is believed they wouldbe less penetrable by moisture and consequently less resistant towashing.

5. A common conception is, or has been, that the soils of thehumid tropics are deficient in organic matter* This conception un-doubtedly is based partly upon the rapidity of vegetable decomposi-tion in the humid tropics. Organic matter does disintegrate anddisappear in these regions with extreme rapidity .under the attackof constant moisture and warm temperature, insects, molds, andbacteria. The general scarcity of forest mold is a result of this;and also the quick decay and disappearance of all plants, which havebeen cut, except those which take root and reestablish themselves.In planting bananas, the underbrush is removed and the seed put intothe ground, when the forest is immediately felled, and the tress leftwhere they fall. Within twelve months the small trees, and brancheshave disappeared, and the huge logs have decayed to the heart, exceptthe;- very hard species, such as liquum vitae and the setaceous palms.

The soils, however, contain as much organic matter, if not more,than those of our own forested lands, even where precipitation amountsto 150 inches annually. Certain conditions here obviously are favor-able to conservation of organic matter in a finely divided state, andthis in some way gets down into the soil*

Leaf mold is present in some places. In a strip of rain foreston the lower northern slope of Turrialba Volcano in Costa Rica, well-

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developed forest mold was found, showing the plug-tobacco and peatlikestructure, and coffee-brown color, characteristic of so much of the leafmold of temperate North America. Similar brown leaf mold was also seenin a number of damp, shady places on the Pacific slope of the Andes,and elsewhere. Also mold was found which was not coffee-brown in color,but yellowish brown and less compact.

Many other soils were seen, some resembling those which have beendescribed, and others markedly dissimilar in characteristics. It willbe possible to refer briefly to a few of these only.

In northeastern Nicaragua there is an extensive coastal plain,which is essentially a duplicate of the Florida flatwoods. The soilshere are highly quartzose. St. Johns fine sand is as well developednear the shores of Pearl Lagoon as it is in St. Johns County, Florida.Norfolk fine sand and fine sandy loam also occur here, and other typesfound in our Atlantic and Gulf plains. In the St. Johns the coffee-brown organic sard hardpan horizon, is developed below the surface justas it is in Florida,

Pine is the characteristic tree over this Nicaraguan plain, andthere are scrub oaks, saw palmetto, and sundew as we find them alongthe southern Atlantic and Gulf seaboards. The change of vegetationfrom the tropical growth of the heavy soils to pine, oak and sawpalmetto on the sandy soils is as sharp as the boundaries that sepa-rate these types. Those plant scientists who claim unqualifiedlythat the pine of Central America ie the result of an impoverishedsoil condition which has resulted from the milpa agriculture ofancient races, and that tropical forest is always encroaching uponpine forest under natural conditions, would find difficulty in ex-plaining away some of the facts encountered in this region. In thefirst place there is no evidence of any extensive agricultural utili-zation of these sandy lands, and secondly, the pine forest is actuallyencroaching upon the tropical type in those places where heavy rainsare causing the sand to wash out into the jungle. The trees followthe soil.

In northern Honduras, there is much red, shallow clay derivedfrom mica schists, which is a duplicate of the Talladega soils inthe southern extension of the crystalline rocks of the Appalachians.This is hilly to mountainous land supporting pine forest with scat-tered oak and sweet gum. Where it comes in contact with the deepfriable clays on the slopes of the Espiritu Santo Mountains nearthe Guatemala boundary there is a change to tropical forests whichagain is precisely marked by the soil boundaries. Not a pine nor anoak was seen beyond the limits of the Talladega stony soils. Nordoes this change appear to be the result of an accident of nature orof human intervention.

Light colored soils derived from volcanic material of high

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pumice content are abundant in the highlands of Honduras, Guatemala,and Salvador, and also dark colored soils derived from the same kind ofmaterial over the Pacific Coastal Plain of Guatemala and Salvador,where there is a. longer and more severe dry season. Collectively,these are known as the talpatate soils. Pine is common on the shallowtalpatate of light color; none was seen on the dark types.

On the inter-mountain high plateaus of central Guatemala, darkreddish clay derived chiefly from volcanic ash is of common occurrence.This appears to be a very old soil. It is much s t i f fer than the darkash soils of the Costa Rican Piedmont lands, but resembles the redlands associated with the dark ash soils. On it corn has been grownwithout fertilization for a very long time, and good yields continueto be obtained - about 50 bushels an acre, according to our ConsulGeneral in the city of Guatemala. The Consul General said that cornhad been grown on these plateaus back to a time when the memory ofman runneth not to the contrary. There is little doubt it was an im-portant crop on the same land in Maya time. It is probable thefields were periodically rested by reversion to bush growth.

Taking now a long jump to South America, we find theMountains of Ecuador north of the latitude of Guayaquil almost whollycovered by soils derived from unconsolidated volcanic ejecta. Inthe more humid localities of the high inter-Andine region there arebrown and black soils, which are very friable owing to their texture.These are generally acid in the surface, but often alkaline in the'parent pumice beds beneath, . In those sections where precipitationfalls below 20 inches, lime carbonate has accumulated in the sub-strata in numerous places. Generally the lime has not accumulatedin the thick beds characterizing our North .American plain region -the caliche beds; but is present more often as pockets and thin dis-continuous seams, such as might be styled incipient caliche.

In this lofty Andine region, one frequently sees buried orfossil soils, that is, soils which have been covered by falls ofvolcanic ash. Exposed sections show a dark colored surface layer,rich in organic matter, overlying a bed of light colored pumicefragments, the two sections representing the recent soil profile;this in turn, is underlain by a dark-colored layer, rich in organicmatter, with a bed of light-colored pumice fragments beneath. Thelower sections duplicate the two upper sections or the soil andsubsoil, in such a way as to leave no doubt as to the mode of origin.

The Andes of Ecuador consist of an eastern and a western range,with lofty snow-covered peaks, Chimborazo, having an altitude of morethan 20,000 feet, These ranges enclose a trough or valley whosefloor ranges from about 8,000 to 10,500 feet elevation. Transverseridges, called nudos, break the valley into sections or basins calledhoyas. Through these, streams flow parallel with the enclosing ranges,filially to break through one side or the other to enter either the

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Pacific or the Atlantic by the

The valley floors and adjacent slopes up to 11,000 feet are largelyeither in cultivation or are utilized for grazing stock. Many slopesare used for crop production, which are 30 steep that the native woodenplow can not be used, all cultivation being by hand implements. Theyare often so steep that without the substantial terraces or walls builtof earthern blocks, and other materials the soil would creep downhillonto the smoother valley fields and meadows. Soil conservation ispracticed with a high degree of skill, and lands are being used whichsupported a dense population long before the Incas, preceding theSpanish conquistadors came up from Peru to conquer the Cara race.Still the lard is producing,' though yields are often small. Irriga-tion is practiced on many farms, water being carried into the drieror desert localities by tunnels and aqueducts of skillful and oftenancient construction.

Corn, potatoes, barley, wheat, beans, alfalfa, fruits , andeucalyptus trees are the principal crop's. Barley and potatoes aregrown up to about 11,000 feet. There ig no indication that treesever grew naturally in the inter-Andine region. The eucalyptus wasintroduced in 1860, and it now largely supplies the wood require-ments of the region. The man, -vdio brought this most valuable plantto the country, President Garcia Moreno, is new honored for hisgreat service to his country. He was murdered by political enemiesand his body dragged through the streets of Quito.

The mountain slope soils aite much the same from the valley floorup to about 14,000 to 15,000 feet, or to the lower limits of rockand snow. Uncultivated areas are covered by a bush growth up toabout 11,000 to 11,500 feet , tongues of this vegetation ascendingstill higher along gulches. Above the bush belt come the grasslands, called paramos. These are wind-swept during day and cold atnight, frosts were encountered even below the paramos, <4, 10,500feet , in December. They are said to occur in June, and severalother months, even in Quito.

When the equator was visited it was so chilly that an overcoatfailed to keep one any too warm. Near this point Cayambe stoodsquarely over the equator - a 19,000 foot peak whose summit isperpetually covered with snow.

Descending the Pacific slope of the Andes, entirely differentvegetative conditions were met with, but the soils were much the samedown to about 3,000 feet* This particular descent was by mule-back,The western Cordillera was crossed through a pass at something over11,000 feet, ^t was sunny and springlike ir the pass, and dandelionsand buttercups were blossoming. Going down, the climate graduallychanged from early spring to late spring then to early summer, midsummer, and finally through subtropical to tropical,

1

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Below the paramo, the brush zone was crossed, then a small treezone known as the ceja de la montana (the eyebrow of the forest); belowthis was light forest, moderately heavy forest, and so on into heavytropical forest, often jungle of inconceivable density.

The trail down ascended and descended mountain sides, sometimeshanging high over the canyon of the Pilaton River, No doubt beautifulviews were to be had, if it had not seemed best to look upward in-stead of downward, owing to the narrowness of the cliff trails.

At about 2,500 feet a great outwash plain was entered. Thisslopes gradually toward the Pacific, and much of it consists of pro-ductive soil of favorable topography. At ono place the accumulatedoutwash was estimated to have a thickness of 800 feet. This changedbut little in character from the bottom of the section up to within afew feet of the surface. Here the soil is a brown loam to fine sandyloam of such a mellow nature that it is possible to dig deeply intoit with the bare hands. Considerable leaf mold is found in the heavyforest.

At the time this zone was entered there had been nearly 7 monthsof dry weather. It was near the close of the dry season, which hereis usually of about 6 months duration, the rainfall of the wet seasonamounting to probably 90 inches. The soil was moist from near thesurface downward, and in spite of the long rainless season, plants\»ere every^-here green and growing, and there was no place, not evenin pastures, "here there was enough dry grass to start a fire, asoil sample collected at Santo Domingo de Los Colorados contains 8per cent of organic matter in the upper 5 inches, 3 per cent between5 and 12 inches, 27 between 12 and 17, 3 per cent between 17 and 34,and 2 per cent between 34 and 60. Another taken at Ha contains 13per cent in the surface inch, 5.6 between 1 and 12 inches, and 3 percent between 46 and 60 inches* Chemically there is not much changedown to 5 feet, except in the organic matter contained. The severalsections of the sample from Santo Domingo de LOS Colorados average60 per cent SiO2, 6 'Fe2O3, 18.6 Al2O3 5 CaO, 2.6 MgO, 1,3 K2O,3 Na2O, and »24 P2O5* The nitrogen ranges from .43 per cent in thetop layer to .1 per cent in the lowest horizon. The content ofmaterial coarser than silt averages 51 per cent and that finer thansilt 24 per cent.

Farther south in the game topographic and climatic belt, thesoil changes to a reddish, highly friable clay containing as muchas 85 per cent of colloidal material and but 2.6 per cent of mater-ial coarser than silt. This, too, is a very productive type of soil.

It is interesting to note that upon returning to the CanalZone after leaving South America, the forests on the Pacific sideof the Isthmus were found to be largely leafless and the grassysavanas so dry that fires were burning in all directions at a time

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•when there had been less than -two months dry season. Some heavilytimbered forests on shallow limestone soil were of desertlike appear-ance, 90 per cent of the trees being completely leafless, and all thegrass parched. This was along the Chagres River where the rainfallamounts to 100 inches. The savanas of Panama were highly desiccated,and the clay soil almost as hard as rock.

The outwash plain soil of Ecuador is one of such favorable physicalcomposition that its moisture holding capacity practically eliminatesthe effect of climate, but the opposite is true of the Panama types re-ferred to. In the case of the former some modifying effect may comefrom the sloping position near the base of a lofty mountain range,and also from the bank of cloud that usually hangs over the westernslope of the Andes. These agencies, however, cculd scarcely accountfor the extreme divergence of soil moisture conditions as comparedwith the Pacific coast of Panama*

There is not time to discuss further the soils of these countries,although some of those seen in the region of perpetual rain in theBuenovetura section of western Colombia, are very interesting. Onthe train between Cali and Buenoventura, a region of absolute desertwith giant cactus, prickly pear, and accacias, was left and one ofheavy tropical forest, where it rains almost daily, was entered with-in 23 minutes time. The vast water-soaked swamp of the AtratoRiver in northern Colombia is an interesting region, as is also thevari-colored soils of the continental divide between the San Juanand Atrato Rivers, at which place our party crossed the South Americancontinent from navigable water on the Pacific side to navigable wateron the Atlantic side by a 3 hours horseback ride. In the extremelywet region of this part of South America the trees are generally small.

The grass lands of Central -America, those of Panama particularly,are worthy of additional study. Some claim these savanas are tree-less because of former agricultural occupation. There are reasonsto believe they are treeless because of natural unfavorable soilconditions. Additional studies, covering larger areas, stccldbe made of the savanas of this region.

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