The extent, then, to which the two stocks that occupy the British Isles are pure or mixed; the characteristics of each stock in its purest form; and the effects of intermixture where it has taken place, are some of our problems; and if they could each and all be satisfactorily answered, we should have a Natural History of our Civilization. But the answers are not satisfactory; at any rate they are not conclusive. Nevertheless, a partial solution can be obtained; a partial solution which is certainly worth some efforts on the part of both the reader and the writer. Other questions, too, curious rather than of practical value, constitute the department of minute ethnology; especially when the area under notice is an island. The _date_ of its occupancy, although impossible as an absolute epoch, can still be brought within certain limits. Whether, however, such limits would not be too wide for any one but a geologist, is another question. Now, if I have succeeded in shewing that criticism and disquisition must necessarily form a large part of such an ethnology as the one before us, I have given a reason for what may, perhaps, seem an apparent irregularity in the arrangement of the different parts of the subject. With the civil historian, the earliest events come first; for, in following causes to their consequences, he begins with the oldest. The ethnologist, on the other hand, whenever--as is rarely the case--he can lay before the reader the whole process and all the steps of his investigations, reverses this method, and begins with the times in which he lives; so that by a long series of inferences from effect to cause, he concludes--so to say--at the beginning; inasmuch as it is his special business to argue backwards or upwards. Yet the facts of the present volume will follow neither of these arrangements exactly; though, of course, the order of them will be, in the main, chronological. They will be taken, in many cases, as they are wanted for the purposes of the argument; so that if a fact of the tenth century be necessary for the full understanding of one of the fifth, it will be taken out of its due order. Occasional transpositions of this kind are to be found in all works wherein the investigation of doubtful points preponderates over the illustration of admitted facts, or in all works where discussion outweighs exposition. The period when the British Isles were occupied by Kelts only (or, at least, supposed to have been so) will form the subject of the earlier chapters. The facts will, of course, be given as I have been able to find them; but it may be not unnecessary to state beforehand the nature of the principal questions upon which they will bear. The date of the first occupancy of the British Isles by man is one of them. It can (as already stated) only be brought within certain wide--very wide--limits; and that hypothetically, or subject to the accuracy of several preliminary facts.