If we do this, we are prepared for another question. How far is the introduction of metal implements and of new arts, a sign of the introduction of a fresh stock or variety of the human species? How far, too, is the difference in the capacity of the skulls? How far the fact of the two changes coinciding? The answer has generally been in the affirmative. The men who used implements of bronze were Kelts; the men who eked out their existence with nothing better than adzes and arrow-heads of stone, were other than Keltic. They were ante-Keltic aborigines, whom a Keltic migration annihilated and superseded. Such is the widely-spread doctrine. Yet it is doubtful whether the premises bear out the inference--far as it has been recognized. I doubt it myself; because, admitting (for the sake of argument) that there is a difference in the size and the shape of the skulls, it by no means follows that a difference of stock is the only way of accounting for it. Improved implements, taken by themselves, merely denote either a progress in the useful arts, or, what is more likely, some new commercial relations. The same improved implements, if considered as means to an end, denote an improvement in the nutrition of the individuals who used them. The bones of a man who hunts stags and oxen with bronze weapons will carry more flesh, and consequently be more fuller developed than those of a man who, for want of better instruments than flint and bone arrow-heads, feeds chiefly upon whale blubber and shell-fish. Now, what applies to the bones in general, applies--though perhaps in a less degree--to the skull. In the difference, then, between the crania of the Stone and Bronze periods I see no introduction of a new variety of our species, but merely the effects of a better diet, arising from an improvement in the instruments for obtaining it. If the assumption, then, of a _pre_-Keltic stock be gratuitous, the question as to the date of our population is considerably narrowed. Its introduction (as already indicated) must have been sufficiently late to allow the original affinities between the Keltic dialects of the British Isles, and the Keltic dialects of the European Continent, to remain visible. But as many millenniums would be required for the opposite effect of obliterating the original similarity, this is saying but little. All that it is safe to assert is-- 1. That the primitive Britons occupied the islands sufficiently _early_ to allow of the relative levels of the land and sea on the valley of the Forth to alter to the amount of twenty-five feet--there or thereabouts. 2. That they occupied it sufficiently _late_ to allow the common origin of the Gaelic and British tongues to remain visible in the nineteenth century. This latter position rests upon the supposition that the early inhabitants in question were of the same stock as the present Welsh and Gaels--the contrary doctrine being held to be, not erroneous, but gratuitous and unnecessary.