Soon after we had mounted our horses in the afternoon, a violent thunder-storm came on from the north-west; hail fell in such quantities, as to cover the surface of the ground, and some of the hail-stones which we examined, were near an inch in diameter. Falling with a strong wind, these heavy masses struck upon our bodies with great violence; our horses, as they had done on a similar occasion before, refused to move, except before the wind. Some of the mules turned off from our course, and had run more than half a mile before they could be overtaken. For ourselves, we found some protection, by wrapping our blankets loosely around our bodies, and waited for the cessation of the storm, not without calling to mind some instances on record of hail-stones which have destroyed the lives of men and animals. It is not improbable, that a climate of a portion of country within the range of the immediate influence {314} of the Rocky Mountains, may be more subject to hail-storms in summer, than any other parts of North America in the same latitude. The radiation of heat from so extensive a surface of naked sand, lying along the base of this vast range of snowy mountains, must produce great local inequalities of temperature. The diminished pressure of the atmosphere, and the consequent rapidity of evaporation, in these elevated regions, may also be supposed to have an important influence on the weather. We have not spent sufficient time in the country, near the eastern range of the Rocky Mountains, to enable us to speak with confidence of the character of its climate. It is, however, sufficiently manifest, that in summer it must be extremely variable, as we have found it; the thermometer often indicating an increase of near fifty degrees of temperature between sunrise and the middle of the day. These rapid alternations of heat and cold must be supposed to mark a climate little favourable to health, though we may safely assert that this portion of the country is exempt from the operation of those causes which produce so deleterious an atmosphere in the lower and more fertile portions of the Mississippi basin. If the wide plains of the Platte, the Upper Arkansa, and the Red river of Louisiana should ever become the seat of a permanent civilized population, the diseases most incident to such a population will probably be fevers, attended with pulmonary and pleuritic inflammations, rheumatism, scrofula, and consumption.[62] It is true, that few, if any, instances of pulmonary consumption occur among the Indians of this region; the same remark is probably as true of the original native population of New York and New England.