As before mentioned, no argument against these views can be drawn from the fact that Thyra's tomb is lined with slabs of oak, while the chamber at Maes-Howe is formed with stone. The difference of the two localities is sufficient to account for this. Denmark has always been famous for its forests, and especially on the shores of the Baltic, at Jellinge, wood of the noblest dimensions was always available, whereas the stone of the country was hard and intractable. In the Orkneys, on the other hand, there is absolutely no timber of natural growth big enough to afford a good-sized walking-stick, and stone is not only everywhere abundant, but splits easily into slabs, self-faced, and most easily worked, so that stone, and stone only, would be the material employed in the Orkneys for that purpose, as wood would also be the best and most available material in Denmark. If, before leaving this branch of the subject, we turn back for a few minutes to the Irish monuments, we are now in a position to judge more correctly of the probabilities of the case than we were. Assuming the three-chambered tumulus at New Grange to have been erected between the years 200 and 400, and Maes-Howe and Jellinge between 800 and 1000 A.D., we have a period of from five to six, it may possibly be seven, centuries between these monuments. Is this more than is sufficient to account for the difference between them, or is it too little? It is not easy to give a categorical answer to such a question, but judging from the experience gained from other styles, in different parts of the world, the conclusion generally would be that the time is in excess of what is required. That there was progress, considerable progress indeed, made in the interval between the Irish and Scandinavian monuments, cannot be denied, but that it should have required five centuries to achieve this advance is hardly what would be expected, and it would be difficult to quote another example of a progress so slow. Yet it is hardly possible to bring down New Grange to the age of St. Patrick (A.D. 436), and as difficult to carry back Maes-Howe beyond Ragnar Lothbrok (794 at the extreme), and between these dates there are only 358 years; but we must certainly add something at either one end or the other; and if we do this, we obtain an amount of progress so slow that it would be almost unaccountable, but upon the assumption that they are the works of two different peoples. At the time the sepulchre on the Boyne was erected, Ireland was energetically and rapidly progressive, and her arts were more flourishing than might have been expected from her then state of civilization. When Maes-Howe was erected, the native population was poor and perishing, and as the lordly Vikings would hardly condescend to act as masons themselves, they did the best they could with the means at their disposal. Explain it, however, as we may, it seems impossible to allow a longer time