To ascertain the relative purity or mixture of a race, a criterion has been adopted by many, who consider it infallible: this is resemblance of face, form, constitution, etc. It is supposed that the purer a race has preserved itself, the greater must be the exterior resemblances of all the individuals composing it. On the contrary, considerable and varied intermixtures would produce an infinite diversity of appearance among individuals. This fact is incontestable, and of great value in ethnological science, but I do not think it quite so reliable as some suppose. Intermixture of races does, indeed, produce at first individual dissemblances, for few individuals belong in precisely the same degree to either of the races composing the mixture. But suppose that, in course of time, the fusion has become complete--that every individual member of the mixed race had precisely the same proportion of mixed blood as every other--he could not then differ greatly from his neighbor. The whole mass, in that case, must present the same general homogeneity as a pure race. The perfect amalgamation of two races of the same group would, therefore, produce a new type, presenting a fictitious appearance of purity, and reproducing itself in succeeding generations. I imagine it possible, therefore, that a "secondary" type may in time assume all the characteristics of a "primary" one, viz: resemblance of the individuals composing it. The lapse of time to produce this complete fusion would necessarily be commensurate to the original diversity of the constituent elements. Where two races belonging to different groups combine, such a complete fusion would probably never be possible. I can illustrate this by reference to individuals. Parents of widely different nations generally have children but little resembling each other--some apparently partaking more of the father's type, some more of the mother's. But if the parents are both of the same, or at least of homogeneous stocks, their offspring exhibits little or no variety; and though the children might resemble neither of the parents, they would be apt to resemble one another.