The climate of Iceland and Greenland in the Middle Ages has been the subject of much controversy, the view that there were extensive changes during that period being warmly upheld by one party and as warmly combated by the other party. The case for climatic change has been well set out by O. Pettersson[7]. The Roman authors (Pliny, Solinus, etc.) wrote that there was a frozen sea about Thule (Iceland), but a party of monks who visited the island about A.D. 795 during the months of February to August, in which the ice is normally most abundant in Icelandic waters, found the coast free, though they met with a frozen sea a day’s journey to the northward. In the ninth century the Norsemen visited Iceland regularly, and at times sailed round it, apparently without interference from ice. The early settlers practised agriculture with some success. In the thirteenth century, however, the reports of ice off Iceland became frequent—apparently the conditions were worse than those of the present day, and much more so than in the eighth and ninth centuries. According to Rabot, it appears from ancient records that considerable areas cultivated in the tenth century are now covered with ice. The first spread of the glaciers took place in the first half of the fourteenth century. In the fifteenth and sixteenth centuries the climate of Iceland ameliorated somewhat, but in the seventeenth there was a readvance, which destroyed several farms about 1640 or 1650. Since then there has been a slight retreat. The ice-conditions of Greenland are closely related to those of Iceland, and the records of the Norse colonization of Greenland bear out the conclusions drawn from the latter island. Up to the close of the twelfth century ice is hardly ever mentioned in the accounts of voyages, though it is now a great hindrance. Eric, the pioneer explorer of West Greenland, spent three successive winters on the islands in Juliaanehaab Bay (latitude 60° 45′ N.), and explored the country during the summer; “this cannot be explained otherwise than by assuming that the Polar ice did not reach Cape Farewell and the west coast of Greenland in those days.” In the thirteenth century ice is first specifically mentioned as a danger to navigation, and at the end of the fourteenth century the old Norse sailing route was on account of ice definitely abandoned in favour of one further south. Shortly afterwards the Norse colonies were wiped out by a southward migration of the Eskimos. Even in Norway itself the fourteenth century was a time of dearth, short harvests and political troubles, when corn had to be imported from Germany instead of being exported to Iceland as in former years. It should be noted that Pettersson’s conclusions are considered invalid by H. H. Hildebrandsson[8] on the ground of the incompleteness of the records.