In the face of this overwhelming mass of definite evidence of the reality not only of the spread of culture and its carriers, but also of the ways and the means by which it travelled, it will naturally be asked how it has come to pass that there is even the shadow of a doubt as to the migrations which distributed this “heliolithic” culture-complex so widely in the world. It cannot be explained by lack of knowledge, for most of the facts that I have enumerated are taken bodily from the anthropological journals of forty or more years ago. The explanation is to be found, I believe, in a curious psychological process incidental to the intensive study of an intricate problem. As knowledge increased and various scholars attempted to define the means by (and the time at) which the contacts of various peoples took place, difficulties were revealed which, though really trivial, were magnified into insuperable obstacles. All of these real difficulties were created by mistaken ideas of the relative chronology of the appearance of civilisation in various centres, and especially by the failure to realise that useful arts were often lost. For example, if on a certain mainland _A_ two practices, _a_ and _b_—one of them, _a_, a useful practice, say the making of pottery; the other, _b_, a useless custom, say the preservation of the corpse—were developed, and _a_ was at least as old, or preferably definitely older than _b_, it seemed altogether inconceivable to the ethnologist if an island _B_ was influenced by the culture of the mainland _A_, at some time after the practices _a_ and _b_ were in vogue, that it might, under any conceivable circumstances, fail to preserve the useful art _a_, even though it might allow the utterly useless practice _b_ to lapse. Therefore it was argued that, if the later inhabitants of _B_ mummified their dead, but did not make pottery, this was clear evidence that they could not have come under the influence of _A_. But the whole of the formidable series of obstacles raised by this kind of argument has been entirely swept away by Dr. Rivers, who has demonstrated how often it has happened that a population has completely lost some useful art which it once had, and even more often clung to some useless practice (=65=). The remarkable feature of the present state of the discussion is that, in spite of Rivers’ complete demolition of these difficulties (=65=), most ethnologists do not seem to realise that there is now a free scope for taking a clear and common-sense view of the truth, unhindered by any obstructions. It is characteristic of the history of scientific, no less than of theological argument, that the immediate effect of the destruction of the foundations of cherished beliefs is to make their more fanatical votaries shout their creed all the louder and more dogmatically, and hurl anathemas at those who dissent.