In such vessels, well stocked with food and weapons, the Northmen were accustomed to spend many weeks together on the sea, now and then touching land. In such vessels they made their way to Algiers and Constantinople, to the White Sea, to Baffin's Bay. It is not, therefore, their voyage to Greenland that seems strange, but it is their success in founding a colony which could last for more than four centuries in that inhospitable climate. The question is sometimes asked whether the climate of Greenland may not have undergone some change within the last thousand years.[195] If there has been any change, it must have been very slight; such as, perhaps, a small variation in the flow of ocean currents might occasion. I am inclined to believe that there may have been such a change, from the testimony of Ivar Bardsen, steward of the Gardar bishopric in the latter half of the fourteenth century, or about halfway between the time of Eric the Red and our own time. According to Bardsen there had long been a downward drifting of ice from the north and a consequent accumulation of bergs and floes upon the eastern coast of Greenland, insomuch that the customary route formerly followed by ships coming from Iceland was no longer safe, and a more southerly route had been generally adopted.[196] This slow southward extension of the polar ice-sheet upon the east of Greenland seems still to be going on at the present day.[197] It is therefore not at all improbable, but on the contrary quite probable, that a thousand years ago the mean annual temperature of the tip end of Greenland, at Cape Farewell, was a few degrees higher than now.[198] But a slight difference of this sort might have an important bearing upon the fortunes of a colony planted there. For example, it would directly affect the extent of the hay crop. Grass grows very well now in the neighbourhood of Julianeshaab. In summer it is still a "green land," with good pasturage for cattle, but there is difficulty in getting hay enough to last through the nine months of winter. In 1855 "there were in Greenland 30 to 40 head of horned cattle, about 100 goats, and 20 sheep;" but in the ancient colony, with a population not exceeding 6,000 persons, "herds of cattle were kept which even yielded produce for exportation to Europe."[199] So strong a contrast seems to indicate a much more plentiful grass crop than to-day, although some hay might perhaps have been imported from Iceland in exchange for Greenland exports, which were chiefly whale oil, eider-down, and skins of seals, foxes, and white bears.