It is not surprising that the water-system of two considerable rivers should furnish strong elements of contrast to those which exist in what is either a table-land or a basin, according as the attention of the investigators is struck by its elevation above the sea, or by its depressions forming salt-lakes--Dead Seas in the way of ethnology. Nor yet is it surprising that such contrasts should have full justice done them in description. Ruins in stone, too, in districts where the most we expect is the embankment or tumulus, strike even the cautious observer with surprise; and fragments of art, however imperfect, create wonder when they represent an industry different from what is found amongst the existing populations of their locality. Whatever may be the exaggeration as to particular descriptions, however, the ethnological deduction is well summed up in the following extract. In describing the tribes of the Gila, the Colorado, and of New Mexico, Gallatin writes, "At the time of the conquest of Mexico, by Cortes, there was _northwardly_, at the distance of 800 or 1,000 miles, a collection of Indian tribes, in a state of civilization, intermediary between that of the Mexicans and the social state of any of the other aborigines."[146] What was the civilization? what the tribes? It is best to express both these facts in as general a way as possible. The _Casas Grandes_ represent the first. The _Pimos_ Indians the second. _The Casa Grande_, or _Great House_.--On the south bank of the Gila, in the midst of a large and beautiful plain, are the ruins of what was called by its discoverers, Fathers Garcias and Font,[147] the _Casa Grande_, a building 445 feet in length, and 270 feet in breadth, with three stories and a terrace; the walls being built of clay, and a wall interrupted with towers investing the principal edifice. [Illustration: Fig. 13.] Later descriptions of Casas Grandes, by eye-witnesses, are those of Lieutenant Emory and Captain Johnston. That of the latter, of one on the River Gila, is as follows:--