If we now take a review of what has been investigated, it is only a coast and a peninsula. What, however, is the state of the interior of that great tract which, politically, lies between Mexico, the United States, and the Pacific, and of which we have the ethnological limits in the areas of the Tototune, the Shasti, the Palaiks, the Paducas, and lastly the Indians of Sonora--for thus far south must we go before we get clear of the _terra incognita_ of California? I am better prepared with suggestions as to the method of investigating these parts than with facts concerning them. 1. In the way of physical geography it is convenient to draw a distinction. The great interior basin (or table-land) of California is one division; the great triangular watershed between the rivers Gila and Colorado another. 2. In the way of new facts we must expect the phænomena of _stone_ architecture, as manifested in the ruins of ancient buildings. 3. In the way of inference we must guard against over-valuing the import of them. They are not upon light grounds to be considered as the measures of a civilization so different from that of the tribes hitherto enumerated, as to suggest the machinery of either unnecessary migrations, or unascertained degradations or annihilations of race. The difference between the great interior basin of California, and the valleys of the rivers Gila and Colorado, with their feeders, is that of a desert and the oases that lie within it. The tribes that inhabit the former are under some of the most unfavourable conditions for sustenance in the world. Some of them, such as those to the east and north, are known to be the more miserable members of the Paduca class. Those of the west are probably extensions of the imperfectly known tribes of the coast, and their analogues in the way of physical influences are to be sought for in Australia rather than in America.