It may now be laid down in which cases it is possible to point with certainty to local differences between the different tribes and reduce to these factors the contradictions which are found. If the same author, who is known to be well-informed concerning the whole area (either personally or through reliable informants), points expressly to such differences, there is no reason to disbelieve him. Many such local differences are indicated in the extensive works of Spencer and Gillen, and Howitt. As an example may be quoted the differences in sexual matters, pointed out by Howitt in _Reports of the Smithsonian Institution_ (compare below, pp. 100 and 101). But even in the case of such reliable authors as the ones just mentioned it should always be carefully considered whether they knew with the same degree of exactness all the tribes they compare. Further, when there is independent information about geographically-separated tribes from reliable authors of the same degree of exactness, to whose information we have reason to ascribe the same weight, we may also safely point, if there are any contradictions, to local differences. But if quite contradictory statements about some tribe or tribes living in close neighbourhood are given, we hardly feel inclined to attribute these contradictions to local differences. A very important indication of the advisability of introducing the element of geographical differences is further the question whether the tribes in question are in general different from each other, and whether they belong to different types of culture. Although very little can be said on that point, still on quite broad lines we must, _e. g._ acknowledge that the Kurnai were a tribe with many singularities, that the Arunta and other Central tribes clearly differ from the S.E. tribes, etc. As we shall make very little use of the geographical factor, what is said above may be considered sufficient on that point.[36] [36] As far as I see, in the present state of our knowledge, it is only admissible to speak with greatest care and in very broad lines of the Australian types of culture. Interesting attempts have been made in this direction by Dr. Graebner, Mr. N. W. Thomas, and Father Schmidt. The two latter especially base their work on a profound and extensive knowledge, and formulate their results with the utmost reserve and carefulness. Fr. W. Schmidt has at his disposal the powerful instrument of linguistic knowledge. Mr. W. N. Thomas knows the Australian facts as nobody else does. Their conclusions are therefore of much weight. The present investigations afford little opportunity to point out geographic differences. Compare Fr. W. Schmidt, "Die Stellung, d. Aranda," etc., _Z.f.E._, 1908, pp. 866 _sqq._; F. Graebner, _Ibid._, 1905, pp. 28 _sqq._; _Globus_, xc. Consult also N. W. Thomas, _Kinship_, and the same, _Z.f.E._, 1905.