Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/762

Rh 744 [DISTRIBUTION. dinary degree to the process. But compared with the remaining Regions of the globe, the Neotropical, as it will be essayed to show in the sequel, presents, perhaps, no greater difficulty in this respect than others do. The Sub- regions (one excepted), however, cannot be said to be well defined, for no natural boundaries are to be found for them, and we must trust solely to the presence or absence of certain forms of Bird-life in marking out their limits. This is, of course, the most proper zoological method of proceeding, but in some cases it tends to make the divi sions rather more than less arbitrary, and in all cases de pendent upon the amount of investigation which has been ical bestowed on the several districts. The physical features res of O f t ne continent of South America are very varied, and a cannot be said to assist us much or at all in our task. The proximity of its southern extremity to an ocean wherein at one season of the year floating ice abounds, gives that portion a rigorous climate, and the presence of the grand chain of the Andes, the highest save one in the world, prolongs beyond the equator those characteristics of a mountainous or even an alpine tract, which override any that are commonly associated with degrees of latitude. This range, the great Cordillera, has also a remarkable effect first on the climatological properties of the whole country, and then on its vegetation, which, of course, acts directly on its animal inhabitants. Running as the Andes do pretty nearly longitudinally, and lying near the western coast of the continent, the warm, moist winds from the Atlantic sweep across its eastern and wider portion, unim peded in their course by any considerable high land, till they are attracted by the summits of the giant range, and, precipitating their fertilizing showers on its lofty slopes, supply the brimming floods of some of the largest rivers of the world. Westward of the chain is in great part a desert, at least down to lat. 10 S., though much of this was, prior to the conquest of Peru by the Spaniards, care fully irrigated and highly luxuriant. A few other arid tracts are found, but compared with most other continents the proportion of desert-land is small, and the valleys of the majestic rivers which roll their course to the Atlantic are clothed with the most extensive virgin forests in the world. To these varied physical conditions seem due the chief differences which are observable in the avifauna of the component parts of the South-American continent, which, rich as it is beyond that of all other countries in genera and species, displays yet a considerable uniformity in its larger groups of Birds. ts of The Subregions into which that portion of the earth x Sub- at present under consideration can be most conveniently ns&amp;gt; separated seem to be six in number four of them included within the continent of South America, and two lying be yond its limits. 1 But the confines of these continental Subregions, as has been above hinted, are of the vaguest- It is doubtful whether any amount of local knowledge will ever justify the zoogeographer in drawing an absolute line of demarcation between any two of them. At present our information certainly does not permit us to do more than indicate the general direction of such boundaries ; not that we believe that their existence may not be legitimately assumed. Beginning with the apex of the continent, we have a Subregion, extending from Cape Horn to somewhere north of Bahia Blanca on its eastern coast, whence its boun dary runs in a north-westerly direction, passing to the east ward of Mendoza, and then northw r ard along the eastern and higher slopes of the Andes until it crosses the equator, 1 In arriving at this conclusion the author wishes to acknowledge the kind assistance he has received from his old friend Mr Salvin, F.R.S., whose long-continued study of American, and especially Neo tropical, forms of birds has placed him in the front rank of authorities on the ornithology of the New World, and, after trifurcating on either side of the valleys of the Magdalena and its confluent the Cauca, returns along the western slopes of the lofty Cordillera, until it trends sen- ward and reaches the Pacific coast of South America some where about Truxillo, in lat. 7 S. This Subregion, for a reason presently to be given, may be called the Patagonian, though its northern extremity lies so far removed from its eponymic territory. Next we have what may be called the Brazilian Subregion, marching with the foregoing until somewhere near Potosi in Bolivia, whence it turns to the north-east, and, avoiding the watershed of the Amazon;-, strikes, perhaps, the Paranahyba, through or along which it makes its way to the Atlantic. Then comes the enor mous basin of the Amazons the Mediterranean of South America, as the dwellers on its banks fondly call it which, though forming an important part of the Brazilian Empire, seems undoubtedly to be a distinct Subregion from that to which this last name has been applied, and may justly be denominated the Amazonian. Yet, be it remembered, that, its peculiarities not being observable on the higher tributaries of the mighty river, its upper waters must be regarded as draining land which belongs to the fourth Subregion of which more immediately. Continuous to the southward with the Brazilian boundary the western frontier of the Amazonian Subregion seems to turn off before the eastern confines of the Patagonian Subregion are reached, and, leaving a space intervening, it pursues a generally northward course, at a lower level, on the western bank of the Huallaga, and crossing the great stream whence it derives its name, in somewhere about long. 77 W. and lat. 5 S., it pursues its way towards the mouth of the Orinoco. The fourth and last Subregion of South America includes all that is left of the continent, and perhaps may be most fitly named the Subandean. 2 This begins in the south with the narrow slip of land before mentioned as intervening between the comparatively low-lying Ama zonian Subregion and that portion of the Patagonian which runs along the lofty Peruvian Andes, and is believed to extend from the frontiers of Bolivia to the table-land of Ecuador, rounding, on the one hand, the forked extremity of the Patagonian Subregion to the westward until it meets the Pacific at Truxillo, stretching over 500 miles of sea to the Galapagos Islands, under the equator, and, on the other hand, following the Amazonian boundary to the Atlantic, while it comprehends the islands of Trinidad and Tobago, as well as those which lie on the northern coast of South America. Besides portions of the states already named, it includes Nueva Granada and Venezuela till it reaches the Central-American Subregion in the Isthmus of Panama. This fifth Subregion stretches on the west northward about as far as Guaymas on the east coast of the Gulf of Cali fornia, and on the east to the Rio Grande, which forms the boundary of Mexico and Texas, but the Nearctic Region dips down along the central table-land till near Queretaro, a little to the northward of the city of Mexico, and thence southward along the higher ridges to an almost indefinite extent. The sixth Subregion is composed of the Antilles, with the important exception of Trinidad and Tobago, and its limits being capable of easy geographical circumscrip tion, further consideration of them may be for the present deferred. The difficulty of distinguishing these several Subregions is indeed very great ; and it is not only possible, but highly probable that even in a few years further exploration will enjoin a large amount of rectification of their frontiers. It 2 In some respects it corresponds with what has been commonly called the &quot; Columbian &quot; Subregion ; but that name, having been used in a special and more restricted sei&amp;gt;?e, might give rise to some mis understanding. As will be seen, it comprehend? far more than the former United States of Columbia.