The portion of country which we design to consider under this division has an average width of five or six hundred miles, extending along the base of the Rocky Mountains from north to south: as far as we have any acquaintance with that range, consisting entirely of granitic sands, or of secondary aggregates made up of the _detritus_ of that great chain of primitive mountains, there seems to be a degree of propriety in designating it by some name recognising relation to those mountains. It has been mentioned as the "Mexican desert;" a name sufficiently applicable, perhaps, to some portions of it, but one by no means to be extended to every part alike, as there can be little doubt of its occupying an extensive {277} portion of the interior of North America. That a similar desert region exists on the western side of the mountains, we have sufficient evidence; but whether as uninterrupted and as extensive, we have not the means of determining. The Jesuit Venegas, speaking of the early history of California, says "Father Kino and his companions, after travelling thirty leagues from San. Marcelo, came to a small rancheria (Indian village); and leaving on the north the great mountain of Santa Clara, whose sides, for the length of a league, are covered with pumice-stone, they arrived at the _Sandy Waste_, on the 19th of March." Our information is, however, too limited to justify an attempt to fix the boundaries of this desert; we will, therefore, content ourselves with communicating the observations our opportunities have enabled us to make.