measuring less than 156,000 sq. m. In explanation of this great diversity of speech several theories have been put forward. One is to the effect that here, as in the region of the Caucasus in the Old World, the multiplicity of languages is due to the fact that tribe after tribe has been driven into the mountain valleys, &c., by the pressure of stronger and more aggressive peoples, who were setting forth on careers of migration and conquest. Another view, advocated by Horatio Hale in 1886 (_Proc. Amer. Assoc. Adv. Sci._; also _Proc. Canad. Inst._, Toronto, 1888), is that this great diversity of human speech is due to the language-making instinct of children, being the result of "its exercise by young children accidentally isolated from the teachings and influence of grown companions." A pair of young human beings, separating thus from the parent tribe and starting social life in a new environment by themselves, would, according to Mr Hale, soon produce a new dialect or a new language. This theory was looked upon with favour by Romanes, Brinton, and other psychologists and ethnologists. Dr R. B. Dixon (_Congr. intern. des. Amér._, Quebec, 1906, pp. 255-263), discussing some aspects of this question, concludes "that the great linguistic and considerable cultural complexity of this whole California-Oregon region is due to progressive differentiation rather than to the crowding into this restricted area of remnants of originally discrete stocks." How far two dialects of one stock can go in the way of such differentiation without becoming absolutely distinct is illustrated by the Achomawi branches of the Shastan family of speech, which Dr Dixon has very carefully investigated.