At this point it will be well to remind the reader that the area occupied by the cattle-keeping races whom we have enumerated was continuous. There was no insuperable barrier between Indian and Persian, Persian and Mede, Mede and the dweller in Mesopotamia, or again, between Persian and Armenian, Armenian and the Scythian who lived in his ox-waggon on the plains of what is now Southern Russia: the Scythian was in contact with the tribes of the Balkan Peninsula, who in turn were in contact with the Greeks and the dwellers along the valley of the Danube, who in their turn joined hands with the peoples of Italy, Helvetia and Gaul. Hence the value of cattle would be more or less constant from one end of this entire region to the other. The purchasing power of the cow might be greater in some parts than in others, just as with ourselves a sovereign has the same value from Land’s End to John o’Groats, although the purchasing power of the sovereign as regards the necessaries of life may differ widely in different places within the limits of Great Britain. It is only when some impassable natural barrier intervenes that there will be a difference in the value of the unit of barter. Thus, in the case of Britain we cannot suppose that the value of oxen was necessarily the same there as it was on the Continent. If it was it would be merely a coincidence. The difficulty of transporting live cattle in such ships as the Gauls or Britons possessed would have been too great to permit of such a free circulation of the unit as would have kept its value exactly even on both sides of the Straits. In fact it was only with the invention of steam that facilities for transmarine cattle-trading came in which could tend to level the value on both sides of an arm of the sea. In the earlier half of this century cattle were extraordinarily cheap in Ireland in proportion to the prices which they fetched in England, but yet the difficulty and expense entailed in sending them across in sailing ships effectually prevented the export. When the first steamers began to convey cattle from Ireland to England the profits were enormous, although the freight of a single cow cost, I believe, several pounds. Steam-power has done much to equalize prices, but still there is a considerable difference in the value of cattle on both sides of the Irish Sea. But where no impassable barrier of sea or forest intervened, we may fairly assume the ox carried much the same value from Northern India to the Atlantic Ocean.