PLAINS. 



PLAINS. 



Ml 



logical oWrvatioua ibow DO lack of moisture in that district, the 

 " .jipitation being fully equal u> what it U in the well-wooded 

 farther *t io the Mine latitude. Beaides, UM growth of 

 s U rich and abundant all through the prairie region, under 

 certain conditions of aoil and position, ahowing that their range ia not 

 hnutotl by any general climatologies! cauae. 



ang into oooaideration all the circumstance* under which the 

 peculiar vegetation of thr prairie oocura, we are diapoaed to consider 

 the nature of the soil aa toe prime cauae of the absence of foreata and 

 the predominance of the grasses over this widely extended region. 

 And although chemical composition may not be without influence in 

 bringing about thia reault, which is a queetion for farther investigation, 

 and one worthy of careful examination, yet we conceive that the 

 extreme fineness of the particle* of which the prairie aoil is composed 

 U probably the princi]l reason why it ia better adapted to the growth 

 of ita peculiar vegetation, than to the development of forest*. It 

 cannot fail to strike the careful observer that whero the prairie 

 occupies the surface, the soil and superficial material have been so 

 finely comminuted as to be almost in the state of an impalpable 

 powder. This is due partly to the peculiar nature of the underlying 

 rocks and the facility with which they undergo complete deoomposi- 

 ti !). anil partly to the mechanical cause* which have acted during 

 and since the accumulation of the aediuieutary matter forming tin- 

 prairie soil. 



If we go to a thickly- wooded region, like that of the northern 

 peninsula of Michigan, and examine those portions of the surface 

 which have not been invaded by the forest, we shall observe that the 

 beds of ancient lakes, which have been filled up by the slowest possible 

 accumulation of detrital matter, and are now perfectly dry, remain 

 aa natural prairies, and are not trespassed on by the surrounding 

 woods. We can conceive of no other reason for this than the extreme 

 fineness of the soil which occupies these basins, and which U the 

 natural result of the slow and quiet mode in which they have been 

 filled up. The sides of these depressions, which were once lakes, slope 

 very gradually upwards ; and being covered with a thick growth of 

 vegetation, the material brought into them must have been of the 

 finest possible kind, as U proved to have been the case by examina- 

 tion. Consequently, when the former lake has become entirely 

 filled up and raised above the level of overflow, we find it covered 

 with a most luxuriant crop of gross, forming the natural meadows 

 from which the first settlers are supplied with their winter store of 

 fodder." 



The philosophical geologist may with advantage compare this 

 part of Mr. Hall's statement and reasoning with those of Mr. O. 

 j'oulett Scrope and Sir C. Lyell respecting tin- formation of the 

 Limagne d'Auvergne, or valley of the Allier, which wax once the 

 largest of three or four freshwater lakes existing in the miocene or 

 middle division of the Tertiary period, in the country which is now 

 Central France. The deposition of the fine lacustrine sediment which 

 constitutes the marls and a part of the limestone of the Limagne, in an 

 age characterised by numerous extinct mammals and reptiles, offers a 

 curious parallel to that of the corresponding sediment of the ancient 

 American lakes, forming the soil of the prairie basins, as described by 

 Mr. Hall, at a much later period of the earth's history, one which may 

 be said almost to connect the present with the latest pre-historic era. 

 Nothing con be more different than the present geographical configura- 

 ration and aspect, and geological structure, of the two regions ; but 

 the illustration which the comparison affords of the identity of geo- 

 logical causes in all periods, is most interesting and instructive. It 

 suggests also the inquiry whether evidence can be obtained that at any 

 epoch in the process of filling up of the basins of the ancient lakes of 

 Auvergne, and formation of similar lacustrine plains in other put* of 

 the world, the prairie condition intervened. The discovery of organic 

 remains indicating the former existence of the peculiar prairie sou and 

 vegetation would of course afford that evidence. In North America 

 itself it would be equally important to ascertain whether any pleiocene 

 or pleistocene formations present similar evidence of ancient prairies. 

 See Scrope's 'Geology and Extinct Volcaaos of Centra] France,' 

 ch. ii., and Hall's ' Report,' cited above. 



" Applying these facto," Mr. Hall continues, " to the case of the 

 prairies of larger dimensions farther south, we infer, on what seem to 

 be reasonable grounds, that the whole region now occupied by the 

 prairies of the north-west was once an immense lake, in whose basin 

 sediment of almost impalpable fineness gradually accumulated : . . 

 that this Imsin w drained by the elevation of the whole region ; but, 

 at first, so slowly, that the finer }Mrticlcs of the superficial deposits 

 were not washed away, but allowed to renrmi win-re they were 

 originally deposited. After the more elevated portions of the former 

 basin had been laid bare, the drainage becoming concentrated in com 

 paratively narrow channels, tho current thus produced, aided perhaps 

 l.y'a moro rapid rise of the region, acquired sufficient velocity i 



. tli rough the finer material on the surface, wash away a portion 

 I it altogether, and mix the rest so effectually with the underlying 

 drift materials, or with abraded fragments of the rocks in place, as to 

 give rise to a different character of soil in the valleys from that of the 

 elevated land. This valley soil, being much less homogeneous in its 

 composition and containing a larger proportion of coarse material than 

 that of the upland., seems to have been adapted to the growth of 



forest vegetation ; and, in consequence of this, we find such localities 

 covered with an abundant growth uf timber. 



" Wherever there has been a variation from the usual conditions of 

 soil, on the prairie or in the river bottom, there is a corresponding change 

 in th character of taw vegetation Thin, ou the prairie, we sometimes 

 meet with ridges of coane material, apparently deposits of drift, on 

 which, from some local cause, there has never been an accumulation of 

 fine sediment : in such localities we invariably find a growth of 

 timber. This U the origin of the groves scattered over the prairies, 

 for whose isolated position and peculiar circumstances of growth we 

 are unable to account in any other way. 



" The condition of things in the river valleys themselves seems to 

 odd to the plausibility of this theory. In the district which we have 

 more particularly examined, we have found that where the rivers have 

 worn deep and comparatively narrow valleys bordered by precipitous 

 bluff*, there is almost always a growth of forest ; but where the valley 

 widens out, and the bluffs become less conspicuous, indicating a less 

 rapid erosion and currents of diminished strength, there deposition 

 has taken place under circumstances favourable to the accumulation 

 of a prairie soil, and the result has been the formation of the ' bottom 

 prairie,' which becomes so important a feature of the valleys of the 

 Mississippi and Missouri below the limits of Iowa. Where these 

 bottom prairies have become, by any recent change in the course of the 

 river currents, covered with coarser materials, a growth of forest trees 

 may be observed springing up, and indicating by their rapid develop- 

 ment the presence of a congenial soil." 



LLarua. The whole interior of South America, from the mountains 

 of Caracas on the north to the Straits of Magalhoena on the south, is 

 divided by comparatively low transverse ridges, running east and west 

 into three great basins ; that of the Orinoco on the north, that of the 

 Amazon or Maranon in the centre, and that of the La Plata on the 

 south. The first comprises the llanos, vast plains occupying a surface 

 of 260,000 square miles. They may be divided into two principal 

 portions : the first, beginning at the mouths of the Orinoco, extends 

 westward as far as the Andes of New Granada, being bounded on the 

 north by the Caracas, and on the south by the mountainous group of 

 Porimd and the Rio Apure, an affluent of the lower Orinoco. The 

 other portion of the llano.-t, which is twice as extensive as the first, 

 reaches from the Apure on the north to the Caqueta (an affluent of 

 the Maranon) on the south : having the Andes on the west, and the 

 sierra of I'arinu- and the Orinoco on the east. The inclination of these 

 plains is to the east and south, and they are traversed by many 

 streams, which, taking their rise from the eastern slope of the Andes, 

 bear their tributary waters to the Orinoco. As the medium height of 

 the llanos does not exceed 200 feet, the course of the rivers is very 

 slow and often scarcely perceptible. 



The chief characteristic of the llanos, says Humboldt, is the abso- 

 lute wont of hills and inequalities, the perfect level of every part of the 

 soil. Often in the space of 270 square miles there is not an eminence 

 of a foot high. Thin resemblance to the surface of the sea strikes the 

 imagination most powerfully where the plains are altogether destitute 

 of palm-trees, and where the mountains of the shore and of the Orinoco 

 ore so distant that they cannot be seen. This unvarying equality of 

 surface reigns without interruption from the mouths of the Orinoco to 

 the Villa de Aurore and Ospinos under a parallel of 40 miles in 

 length, and from San Carlos to the Caqueta, on a meridian of 600 

 miles. 



There are however, notwithstanding this uniformity of surface, two 

 kinds of inequalities in the llanos. The first, called brantos, are hori- 

 zontal banks of sandstone or limestone standing four or five feet higher 

 than the rest of the plain, and sometimes many leagues in length. The 

 second kind of inequality, called mrta, consists of convex eminences 

 rising to the height of a few fathoms. 



The llanos have different names in different parts : thus, from the 

 Mouth of .the Dragon, the llanos of Cumana, of Barcelona, and of 

 Caracas or Venezuela, follow from east to west, when, turning south- 

 ward from 8 N. lat, between the meridians of 67 40' and 70* 40', we 

 find the llanos of Vorinas, Casuare, the Meta, Quariore, Caguan, and 

 Caqueta. All these are again subdivided. 



The aspect of the llanos is somewhat dissimilar in different places ; 

 but the greatest difference depends upon the seasons. The local 

 dissimilarity arises chiefly from the nature of the palm-trees scattered 

 about, which vary in different places, and also from the greater or less 

 abundance and variety of the dicotyledonous plants which are inter- 

 mixed with the grasses, the height of which latter is also very unequal, 

 being sometimes only a few inches at a distance from the watercourses, 

 and rising to a height of four feet in their vicinity. In this high 

 grass the jaguar, or American tiger, lurks to spring upon the mules and 

 horses that cross the plain. But the season of drought or of rain 

 i -ntin-ly change the aspect of the greater part of the llanos. In the 

 rainy season, says Humboldt, the llanos display a beautiful verdure, 

 I .ut in the time of great drought they assume the aspect of a desert. 

 The grass is then reduced to powder, the earth cracks, the alligators and 

 great serpents remain buried in the dried mud, till awakened from 

 tln-ir long lethargy by the first showers of spring. These phenomena 

 are observed on barren tracts of fifty or sixty leagues in length where 

 the llanos are not traversed by rivers. 



The principal and almost the only trees of the llanos are different 



