On the pampas of La Plata, which is the treeless abode of the wild horses of South America, there are several salt lakes, not many miles distant from the river Quinto, and over these boundless wastes thousands of wild cattle and horses gallop at pleasure, and afford an inexhaustible stock of game for the lasso of the fearless and expert Gaucho. Now it is a well-authenticated fact that those diseases which are so destructive to the horses and cattle of Europe are almost unknown in these regions. I do not mean to assert that these salt lakes of La Plata account for the exemption which this district enjoys from equine diseases; but there is no doubt that the exhalations from them purify the atmosphere, and that their influence extends for many miles because of the open nature of the country. As a natural result, the whole region is constantly kept in a healthy state; for air, charged with the chloride of sodium, must of necessity act as a preventive to everything inimical to health, and pure air we know (though how few really know what that blessing is) is of a paramount importance in the rearing of cattle. The foot-and-mouth disease, comparatively, has never played such havoc as it does in Europe, and pneumonia, which is almost intractable to treatment in this part of the world, and which is frequently fatal when it is complicated with inflammation of the pleura, hardly ever appears in these parts, where stables and farms are not far off from being rudimentary in construction, and would appear to an English farmer, accustomed to the cosy-looking farmsteads of his own country, very ill-calculated for successful farming, and not at all adapted for bringing his cattle and horses to perfection; yet it is just the reverse, for there is no other part of South America so well fitted for the breeding of cattle, and there is no other locality, whether in the Old or New Worlds, so completely free from disease as the open pampas of La Plata. CHAPTER V. GEOLOGICAL FORMATION OF SALT. Sir Isaac Newton, in his incomparable work upon Optics, likens a particle of salt to a chaos, because of its “being dense, hard, dry, earthy in the centre; and rare, soft and moist in the circumference.” This ingenious definition is what one would expect from such an observant and profound investigator; and I do not think that we shall be able to find a better description of a salt-crystal than that which this great philosopher has bequeathed us.