To distinguish the varieties produced by a fusion of proximate races from those which are the effect of intermixture between races belonging to different groups, I shall call the latter _tertiary_ varieties. Thus the woolly-headed negro and the Pelagian are both "primary" varieties belonging to the same group; their offspring I would call a "secondary" variety; but the hymen of either of them with a race belonging to the white or yellow groups, would produce a "tertiary" variety. To this last, then, belong the mulatto, or cross between white and black, and the Polynesian, who is a cross between the black and the yellow.[168] Half-breeds of this kind display, in various proportions and degrees, the special characteristics of both the ancestral races. But a complete fusion, as in the case of branches of the same group, probably never results from the union of two widely dissimilar races, or, at least, would require an incommensurable lapse of time. If a tertiary type is again modified by intermixture with another, as is the case in a cross between a mulatto and a Mongolian, or between a Polynesian and a European, the ethnical mixture is too great to permit us, in the present state of the science, to arrive at any general conclusions. It appears that every additional intermixture increases the difficulty of complete fusion. In a population composed of a great number of dissimilar ethnical elements, it would require countless ages for a thorough amalgamation; that is to say, so complete a mixture that each individual would have precisely the kind and relative proportion of mixed blood as every other. It follows, therefore, that, in a population so constituted, there is an infinite diversity of form and features among individuals, some pertaining more to one type than another. In other words, there being no equilibrium between the various types, they crop out here and there without any apparent reason.