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Notes of a naturalist in South America

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FLORA OF TROPICAL SOUTH AMERICA.

Further reflection, and such incomplete knowledge as I have been able to acquire as to the flora of inter-tropical South America, lead me to the conclusion that the present vegetable population of this vast region is, when we exclude from view a certain number of immigrants from other regions, mainly derived from two sources. There is, in the first place, the ancient flora of Guiana and tropical Brazil, which has gradually extended itself through Venezuela and Columbia, and along the Pacific coast as far as Ecuador, and, in an opposite direction, through Southern Brazil, to the upper basins of the Uruguay, the Paranà, and the Paraguay. The long period of time occupied by the gradual diffusion of this flora is shown by the large number of peculiar species, and not a few endemic genera that have been developed throughout different parts of this vast region, whose nearest allies, however, are to be found in the original home, Guiana or Brazil. Along with this stock, which mainly occupies the lower country, we find, especially in Venezuela, Columbia, and Ecuador, the modified descendants of vegetable types characteristic of the Andes. Of the Andean flora I shall have something to say in a future page; but I may express the belief that if we go back to the remote period when most of the characteristic types of the vegetation of South America came into existence, we must seek the ancestors of the Brazilian flora, and to a large extent also those of the Andean flora, in the ancient high mountain ranges of Brazil, where we now see, in the vast extent of arenaceous rocks, and in the surviving pinnacles of granite, the ruins of one of the greatest mountain regions of the earth.

Early on Easter Sunday morning, April 9, we were off Tumaco, a small place on one of a group of flat islands lying at the northern extremity of the coast of Ecuador.2 These islands are of good repute as having the healthiest climate on this coast. Although close to the equator, cattle are said to thrive, and, if one could forget the presence of a fringe of cocos palms along the shore, the island opposite to us, in great part cleared of forest, with spreading lawns of green pasture, might have been taken for a gentleman’s park on some flat part of the English coast. We here parted with General Prado, ex-president of Peru, who has purchased one of the islands, and hopes to end his days peacefully as a cattle-breeder. Nothing in his manner or conversation announced either energy or intelligence, but it is impossible not to recognize some kind of ability in a man who, having held such a post at such a time, not only succeeded in escaping the ordinary fate of a Peruvian president – his two immediate predecessors having been assassinated – but also in snatching from the ruin of his country the means of securing an ample provision for himself at a safe distance from home.

In the almost cloudless weather that has prevailed for some days, the apparent path of the sun could not fail to attract attention. Being still so near the vernal equinox, this could not be distinguished from a straight line. Rising out of the horizon at six o’clock, the sun passed exactly through the zenith, and went down perpendicularly in the west into the boundless ocean. Who can wonder that this daily disappearance of the sun has had so large a share in the poetry and the religion of our race? In every land, under every climate, it is the one spectacle which is ever new and ever fascinating. Use cannot stale it; and knowledge, which is said to be driving the imagination out of the field of our modern life, has done nothing to weaken the spell.

We awoke next day to find ourselves in the southern hemisphere, having crossed the line about three a.m. As the morning wore on we passed abreast of the Cabo San Lorenzo, and towards evening, keeping nearer to the coast, were within a few miles of Cabo Santa Elena. This forms the north-western headland of the Gulf of Guayaquil, a wide bay that extends fully a hundred miles eastward from the coastline.

At daybreak, April 11, we were inside the large island of Puna, and soon after entered the mouth of the river Guayas. Although it drains but a small district, this has a deep channel, as wide as the Thames at Gravesend, making the town of Guayaquil, which is about thirty miles from its mouth, the natural port for Western Equatorial America. As we steamed northward up the stream, every eye was turned eastward with the hope of descrying some part of the chain of the Andes. It was, indeed, obvious that a great mountain barrier lay in that direction, and beneath the eastern sun dark masses from time to time stood out to view; but along the crest of the range heavy banks of cloud constantly rested, and the summits remained concealed. We knew that the peak of Chimborazo is scarcely more than seventy miles distant from Guayaquil, and is easily seen from the town in clear weather; but we did not know that clear weather is a phenomenon that recurs only on about half a dozen days in the course of the year, and it is needless to say that we did not draw one of these prizes in the lottery. I had been conscious of a distinct change of climate during the preceding night, and this was still more marked after we entered the river. The increase of temperature was but trifling. The thermometer at sea during the two preceding days had ranged from 77° to 79°, and here at nine a.m. it marked only 80°; nor did it ever rise above 84° while we lay opposite Guayaquil. But the sense of oppressive closeness was more or less felt by every one, and, whatever may be the cause, it seems safe to conclude that the notoriety of this city as one of the most unhealthy in South America is intimately connected with it.

PHYSIOLOGICAL EFFECTS OF HOT CLIMATES.

There is, no doubt, much yet to be learned as to the effects of climate on the human constitution, but a few points seem to be sufficiently ascertained. To those whose constitution has been hereditarily adapted to a temperate or cold climate, the enfeebling effect of hot countries depends much more on the constant continuance of a high temperature than on its amount. A place with a mean temperature of 80° Fahr., which varies little above or below that point, is far more injurious to a European than one where intervals of great heat alternate with periods of cooler weather. Still more important, perhaps, is the effect of a hot climate in places where the air is habitually nearly saturated with aqueous vapour. When the temperature of the skin is not much greater than that of the surrounding air, if this be near the point of saturation but little evaporation can take place from the surface. The action of the absorbent vessels is thus checked, and the activity of all the functions is consequently lowered. As it usually happens that the two agencies here discussed act together in tropical countries, the places having a uniform temperature being also for the most part those having an atmosphere heavily charged with vapour, it is easy to understand that Europeans whose vitality is already depressed are especially exposed to suffer from whatever causes induce endemic or epidemic disease. The difficulty in connection with this subject is to explain certain exceptions to the general rule. In several places in the tropics, usually insular stations, where a steady high temperature is combined with the presence of much vapour, the climate is said to have no injurious effects. But the most marked exception seems to be that of seamen. Excluding that large majority whose calling involves frequent changes of climate, there must be now a considerable body of experience respecting those who for a series of years have navigated tropical seas exposed to nearly uniform temperature. I am not aware that there are any facts to sustain the supposition, which might à priori seem plausible, that such a life tends to enfeeble the European constitution.

Between a broad fringe of mangrove swamp, backed by a narrow border of forest on either bank, with little to break the monotony of the way, we reached Guayaquil before ten a.m. Seen from the river, with many large buildings and stores covering more than a mile of frontage on the western bank, and a straggling suburb stretching to the base of a low hill to the northward, the city presents an unexpectedly imposing appearance. The present amount of trade is inconsiderable, but if ever these regions can attain to the elementary conditions of good government the development of their natural resources must entail a vast increase of business. The territory of Ecuador includes every variety of climate, and is in great part thoroughly suited to Europeans. All tropical products are obtainable, and, with good management and kindly treatment, the supply of efficient negro labour at moderate wages is considerable. Among other products of the soil, the tobacco of the country about Guayaquil deserves to be better known. Of the many varieties of the coarser kind which are grown throughout Central and South America, this appears to me the best, as it certainly is the cheapest. The hawkers who came on board sold at less than seven shillings a hundred cigars of very fair quality, making, as I was told, a profit of fifty per cent.

ALLIGATORS OF THE RIVER GUAYAS.

It might be not unworthy of the notice of the great steamboat companies to recommend to their agents some little consideration for passengers who travel to see the world. It commonly happens that on the arrival of a steamer, after the first conference between the agent and the captain, a time is fixed for departure which has no relation to the hour really intended. We were told this morning that the steamer was to start at one p.m. The time was clearly too short for an excursion to the neighbouring country, and the inducement to spend a couple of hours in the streets of such an unhealthy town was very trifling. Two young Englishmen went up the river in a boat with the hope of shooting alligators. These creatures abound along the banks of the Guayas, basking in the mud, and looking from a distance like the logs that are floated down by the stream. Our sportsmen had the usual measure of success, and no more. For a bullet to pierce the dense covering that shields this animal is a happy accident, but it suffices to disturb the creature from his rest, and to induce him to crawl or roll into the river, and to accomplish this is at least a new experience. Through the courtesy of a native gentleman, the travellers were induced to land at a hacienda on the river, where horses were provided, and they galloped back to the town before one o’clock. Meanwhile the Jamaica story was repeated. It was announced that the agent had decided to keep the steamer till three p.m.; and finally we learned that we should remain at our moorings till early next morning.

 

On her last voyage the Islay had started too late; night fell before she cleared the mouth of the river, and, in the dark, she had run down a chatta– one of the cumbrous native barges that ply along the stream. Of fifteen natives in the barge thirteen were saved, three of them by the courage and activity of the chief officer, who jumped into the river to their rescue. Our captain very properly objected to the risk of another similar accident, and decided to wait for daylight. The cause of the delay remained a mystery, for all that was shipped of passengers and cargo was of a kind that did not seem likely to be very remunerative. At first sight it appeared merely as a characteristic of a rude state of society that the country people around Guayaquil are used to embark on the southward-bound steamers with tropical fruit raised by themselves, which they carry to Lima, and even as far as Valparaiso, dispose of at a handsome profit, and then return home. As most of the profit must go into the coffers of the Pacific Steam Company, the motive is not very obvious; but after a little further experience I fully understood it. Even if they clear little more than the price of their passage, these people find their advantage in undertaking an annual expedition of this kind. Apart from the very positive benefit to health, they gain what they like most in the world – a season of absolute idleness, with the amusement of seeing new objects and talking to new people. For the remainder of the voyage the main-deck was crowded and somewhat encumbered by picturesque groups of rough men, some accompanied by womankind, alternating with huge heaps of tropical fruit – pineapples and bananas, a single bunch of the latter sometimes weighing more than a hundred pounds.

GULF OF GUAYAQUIL.

The thermometer scarcely varied by a small fraction from 80° throughout the night and the following day, until we had cleared the Gulf of Guayaquil; and even at this moderate temperature the feeling of lassitude continued as on the previous day. Of the famous mosquitos of the river Guayas we had little experience. They are said sometimes to attack in swarms so numerous and ferocious that, even by day, it becomes difficult for officers and men to manage a ship on the river.

The sun had set on the following evening, April 12, before we were well abreast of Cabo Blanco, the southern headland of the Gulf of Guayaquil, and we saw nothing of its southern shore. About one-half of this belongs to Peru, and close to the frontier-line is the little port of Tumbez, sometimes visited by passing steamers. I was assured by two of the ship’s officers that the climate and vegetation of this place are much the same as at Guayaquil, but there are few parts of the American coast that better deserve careful examination by a scientific naturalist.

During the night of the 12th we passed Cape Parinas, the westernmost headland of South America, and before sunrise were in the roads of Payta. Being aware that the so-called rainless zone of Peru extends northward to this place, I was especially anxious to see as much of it as possible. During the night the temperature had fallen, especially after rounding Cape Parinas, and at sunrise stood at 74°. In the cooler air, and under the excitement of pleasant anticipation, the lassitude of the two preceding days utterly disappeared; and as day dawned I stood on deck, with my tin box slung to my back, ready to go ashore long before there was any possibility of doing so. The officers told me, indeed, that there was no use in taking a botanical box, as the country about Payta was absolutely without vegetation. I have many times had the same assurance given me, but the time had not yet come when I was to find it correct, and I felt that Payta was not one of such rare spots on the earth.

The appearance of the place and of its surroundings is unquestionably very strange, and the contrast between it and the shores of the neighbouring Gulf of Guayaquil is simply marvellous. Saving the presence of a mean little modern church, with two shabby wooden towers coated with plaster, the aspect of the little town reminded me of Suez, with the difference that the surrounding desert is here raised about a hundred feet above the sea-level. The place, I presume, is improved since it was visited and described by Squiers, and I found that on the slope between the base of the plateau and the beach there is ample space for some mean streets.

FLORA OF PAYTA.

With several companions who were kind enough to interest themselves in plant-hunting, I at once turned towards the sea-beach at the south-western side of the town, keeping along the base of the low cliffs that here descend to the water’s edge. The seaward face of the cliffs is furrowed by numerous gullies, and in one of the broadest of these I was delighted to observe numerous stunted bushes well laden with crimson flowers. This turned out to be Galvesia limensis, a plant found only at a few spots in Peru, whose nearest but yet distant European ally is the common snapdragon. In the upper part of the same gully were the withered remains of several other species, most of which have been since identified. Emerging on the plateau, we found ourselves on a wide plain, apparently unbroken, leading up to a range of hills some fifteen or twenty miles distant. Though we were here only five degrees from the equator, and before we returned to the ship the sun had risen as high as on a summer’s noon in England, the southerly breeze felt delightfully cool and fresh, and at midday, under the vertical sun, the temperature on board ship was not quite 75°.

Vegetation, as I anticipated, was not entirely absent from the plateau, but it was more scarce than I had anywhere seen it, except in the tracts west of the Nile above Cairo, where the drifting sands covers up and bury everything on the surface. In the northern Sahara, about Biskra, where rain is much less infrequent than here, vegetation, though scanty, is nearly continuous, and it is not easy to find spaces of several square yards absolutely without a single plant. About Suez, and on parts of the isthmus where a slight infiltration from the sweet water canal has not developed a more varied vegetation, the number of species in a given tract is often very limited; but tufts of vigorous growth, especially of the salt-loving species, are seen at frequent intervals. On the plateau of Payta, where, as we rambled about, several pairs of eyes were on the alert, but a single tuft of verdure visible at a distance could be made out. This was formed by several bushes of Prosopis limensis growing together. Elsewhere the few plants seen were confined to the occasional shallow depressions where rain rests longest. All, of course, had perennial roots, and scarcely one of them rose as much as three inches from the ground.3

I found it difficult to account for the origin of the sands which are sparingly scattered over the plateau, but accumulated to a considerable depth on the slopes behind the town. The underlying rock seen in ascending to the plateau is a tolerably compact shale; but the hard crust forming the superficial stratum appears to consist of different materials, and not to be made up from the disintegrated materials of the shale. At several places, both below the cliffs and on the plateau, I found large scattered fragments of what appeared to be a very recent calcareous formation, largely composed of shells of living species; but this was nowhere seen in situ, and I was unable to conjecture the origin of these fragments.

CLIMATE OF NORTHERN PERU.

Before returning to the Islay, I had the advantage of a short conversation with the very intelligent gentleman who acts as British consular agent at Payta, and whose ability would perhaps be seen to advantage in a more conspicuous post. The information received from him fully confirmed the impressions formed during my short excursion. The appearance of the gullies that furrow the seaward face of the plateau sufficiently showed that, however infrequent they may be, heavy rains must sometimes visit this part of the coast. I now learned that, in point of fact, abundant rain lasting for several days recurs at intervals of three or four years, the last having been seen in the year 1879. As happens everywhere else in the arid coast zone, extending nearly two thousand miles from Payta to Coquimbo in North Chili, abundant rainfall is speedily followed by an outburst of herbaceous vegetation covering the surfaces that have so long been bare. During the long dry intervals slight showers occur occasionally a few times in each year. These are quite insufficient to cause any general appearance of fresh vegetation, but suffice, it would seem, to maintain the vitality of the few species that hold their ground persistently. The ordinary supply of water in Payta, obtained from a stream descending from the Andes seventeen miles distant, is carried by donkeys that are despatched every morning for the purpose. There was something quite strange in the appearance of a few bundles of fresh grass which we saw in the plaza. They had come that morning by the same conveyance for the support of the very few domestic animals that it is possible to keep in such a place.

The problems suggested by the singular climatal conditions of this region of South America have not, I think, been as fully discussed as they deserve to be, and I here venture on some remarks as a contribution to the subject.

The existence of the so-called rainless zone on the west coast of South America is usually accounted for by two agencies whose union is necessary to produce the result. The great range of the Andes, it is said, acts as a condenser on the moisture that is constantly carried from the Atlantic coasts by the general westward drift of the atmosphere in low latitudes. The copious rainfall thus produced on the eastern slopes of the great range leaves the air of the highlands of Peru and Bolivia relatively dry and cool, so that any portion that may descend to the coast on the western declivity tends to prevent rather than to cause fresh aqueous precipitations. Meanwhile the branch of the Antarctic Ocean current known as the Humboldt current, which sets northward along the sea-board from Western Patagonia, is accompanied by an aërial current, or prevailing breeze, which keeps the same direction. The cold air flowing towards the equator, being gradually warmed, has its capacity for holding vapour in suspension constantly increased, and is thus enabled to absorb a large portion of the vapour contained in the currents that occasionally flow inland from the Pacific, so that the production of rain is a rare event, recurring only at long intervals. Admitting the plausibility of this explanation, a first difficulty presents itself. If the Andes act as a barrier against the vapour-laden atmosphere of eastern tropical America throughout Peru, Bolivia, and Northern Chili why, it may be asked, do they fail to perform the same function in Ecuador and Colombia? Whence the absolute contrast in point of climate that exists between these regions? Why is the littoral zone between the Gulf of Guayaquil and that of Panama, a distance of some eight hundred miles, not merely less dry than that of Peru, but actually more moist than most parts of the coast of Brazil or Guiana?

 

CAUSES OF THE ARID COAST CLIMATE.

Some answer may, I think, be given to these questions. In the first place, comparing the orography of Peru and Bolivia with that of Ecuador, some important differences must be noted. In Eastern Peru, as is at once shown by the direction of the principal rivers, we find no less than four parallel mountain ranges, increasing in mean elevation as we travel from east to west. The westernmost range, to which in Peru the name Cordillera is exclusively applied, does not everywhere include the highest peaks, but has the highest mean elevation. The second range, exclusively called Andes in Peru, rivals the first in height and importance. I know of no collective names by which to distinguish the third range, dividing the valley of the Huallaga from that of the Ucayali, nor the fourth range, forming the eastern boundary of the latter stream. In South Peru and Bolivia the mountain ranges are less regularly disposed, but cover a still wider area; and throughout the whole region it is obvious that the warm and moist currents drifting slowly westward have to traverse a zone of lofty mountains varying from four to six hundred miles in width, and can carry no moisture available to produce rain on the western seaboard. In Ecuador the two principal ranges – the Cordillera and the Andes – are much nearer together than they usually are in Peru, and no parallel ranges flank them on the east. The numerous tributaries of the Maranon flow in a tolerably direct course east or south-east, many of them rising within a hundred and fifty miles of the Pacific coast. It follows that the atmospheric currents meeting less preliminary obstruction reach the eastern slopes of the main range still very heavily charged with vapour. In crossing the barrier a large portion of the burthen must be deposited; but it is probable that a large amount is nevertheless carried to the western side of the range.

It may be said that this explanation, whatever it may be worth, cannot apply to the territory of Colombia, where the Andes are broken up into at least three lofty ranges, and the mountains cover as wide a space as they do in Peru. My impression is that the abundant supply of moisture on the west coast of Colombia arises from a different source. The effects of the Isthmus of Panama as a barrier against atmospheric currents must be absolutely insignificant, and I have no doubt that those which flow eastward along the coast of the Caribbean Sea are in part diverted south-east and south along the west coast of Colombia.

There can, however, be little doubt that in determining the climate of the west coast the influence of the Humboldt current, and of the cool southerly breezes that accompany it, is far greater than that of the disposition of the mountain ranges. A glance at the map shows that about the fifth and sixth degrees of south latitude the direction of the coast undergoes a considerable change. On the voyage from Panama, we had hitherto steered somewhat west of south; henceforward our course lay between south-south-east and south-east. All the currents of the ocean and atmosphere, whose existence arises from the unequal distribution of heat on the earth’s surface, vary somewhat in their course throughout the year with the changes of season, and this doubtless holds good on the American coast. I believe, however, that both the sea and air currents from the south are normally deflected away from the coast at the promontory of Ajulla (sometimes written “Ahuja”), a short distance south of Payta. A further portion is again deflected westward at Cape Parinas, north of which headland they seem not to be ordinarily met. I infer, however, from the testimony of seamen, that at some seasons they are felt near the coast as far north as the equator, and even beyond it. This inference was confirmed by observing the parched appearance of the seaward slope of Cabo Sta. Elena, north of the Gulf of Guayaquil, which apparently does not fully share in the frequent rains that elsewhere visit the coast of Ecuador.

INFLUENCE OF THE HUMBOLDT CURRENT.

Whatever force there may be in the above suggestions, I confess that they do not seem to me adequate to account for the extraordinary difference of climate between places so near as Payta and Tumbez – not quite a hundred miles apart – and I trust that further light may be thrown upon the matter by a scientific traveller able to spare the necessary time. So far as I know, no such abrupt and complete a change is known elsewhere in the world. I was unable to obtain any information as to a range of hills or mountains, marked in Arrowsmith’s map “Sa. Amatapi,” which appears to extend east or east-north-east from Cape Parinas. Its height can scarcely be considerable, as it does not appear to have attracted the attention of the seamen who are familiar with this coast; but, on the other hand, there is some reason to think that the southerly breezes prevailing on the coast do not extend to any great height above the sea-level. It would be interesting if we should find on the opposite sides of a range of unimportant hills the same contrasts of climate and vegetation that are known to prevail between the eastern and western slopes of the Peruvian Andes.4

Along the coast of Northern Peru are numerous small islets, evidently at some period detached from the continent either by subsidence or by marine erosion. Here, in the almost complete absence of rain, were formed those secular accumulations deposited by sea-birds, which, when known in Europe under the name of guano, suddenly rivalled the mines of the precious metals as sources of easily acquired wealth. The two most considerable groups are respectively named Lobos de tierra and Lobos de afuera; a smaller group near to Payta is also called Lobos. At the western end of the largest of the latter group the waves have excavated a natural arch, which, after a sufficient period of further excavation, will fall and give rise to a new detached islet. A brisk southerly breeze made the air feel cooler than it had done since we entered the tropics, as we ran about due south until sunset, when, after passing abreast of the promontory of Ajulla, our course was altered to nearly due south-east. I was assured by a native passenger that the promontory of Ajulla, for a distance of thirty or forty miles, is an absolute desert, without a drop of water or the slightest trace of vegetation. Experience has made me somewhat sceptical as to statements of this nature made by non-scientific observers. During the day we frequently observed a fish which appears distinct from the flying-fish of the Atlantic. The pectoral fins appear to be less developed, and in consequence the flight is shorter, and the animal seems to have less command over its movements.

GUANO ISLANDS.

Our course on April 14 lay rather far from land. It was known that yellow fever had broken out at Truxillo, and it was decided that we should run direct to Callao, without touching at that or any of the smaller places on the coast sometimes visited by the steamers. Although the air appeared to be somewhat hazy, the range of the Cordillera, more than a hundred miles distant, was distinctly seen in the afternoon. Very soon after we ran into a dense bank of fog, in which we were immersed for several hours, our cautious captain remaining meanwhile on the bridge, and the frequent cry of the steam-whistle ceased only when we steamed out of the fog into a brilliant star-lit night.

LOW TEMPERATURE OF THE COAST.

These fogs, which are frequent along the Peruvian coast, are the chief, if not the only, difficulty with which the navigator has to contend. When they rest over the land it becomes extremely difficult to make the ports, and at sea they involve the possible risk of collision. If this risk is at present but slight, it must become more serious when intercourse increases, as it must inevitably do if the Ship Canal should ever be completed; and for the general safety it may be expedient to prescribe special rules as to the course to be taken by vessels proceeding north or south along the coast. The origin of the fogs must be obvious to any one who considers the physical conditions of this region, to which I have already referred. The air must be very frequently near the point of saturation, and a slight fall of temperature, or the local intermixture of a body of moister air, must suffice to produce fog. The remarkable thing is that this should so very rarely undergo the further change requisite to cause rain. To some young Englishmen on board, the remarkable coolness of the air along this coast was a continual subject of jesting comment; and on more than one occasion the “Tropics” were emphatically declared to be “humbugs.” It is certain that for thirty-six hours before reaching Callao the shaded thermometer never reached 70°, and stood at noon, with a clear sky and a brisk southerly breeze, no higher than 68°.

2Much cinchona bark, coming from the interior, was formerly shipped at Tumaco; but between horrible roads and the reckless waste of the forests through mismanagement, but little is now conveyed by this way.
3For a list of the species collected, see the Journal of Linnæan Society, vol. xxii.
4The abrupt change in the vegetation on this part of the American coast has been noticed by Humboldt, Weddell, and other scientific travellers. In a note to the French edition of Grisebach (“Vegetation du Globe,” traduit par P. de Tchihatcheff, ii. p. 615), M. André expresses the opinion that this, as well as some other cases of abrupt change in the vegetation observed by him in Colombia, are to be explained by the nature of the soil, which in the arid tracts is sandy or stony, and fails to retain moisture. Admitting that in certain cases this may afford a partial explanation of the facts, it is scarcely conceivable that the limit of the zone wherein little or no rain falls should exactly coincide with a change in the constitution of the soil, and I should be more disposed to admit a reversed order of causation, the porous and mobile superficial crust remaining in those tracts where, owing to deficient rainfall, there is no formation of vegetable mould, and no accumulation of the finer sediment forming a retentive clay.