Page:The Journal of geology (IA journalofgeology21894univers).pdf/149

epiglacial lakes without filling them up in any considerable degree. The ice melted so speedily away, and the crust swelled up so fast, that the deposits of the rivers just below the epiglacial terrace level are very small. This could only occur with a climate more genial than the present in which an existing glacier as great as the epiglacial land ice would certainly assert itself with success.

We must suppose a considerable uplift of the snow line in this time which followed the epiglacial period, and which I shall call the Boreal period. Such a genial climate in early postglacial time we are forced to assume also on biological reasons. On the warm valley sides in the western interior fjords, we find many plants which can only prosper in a temperature more than 2° C. higher than now prevails in the intervening tract across which they must necessarily have immigrated. On the southwestern coast flourished a vegetation almost like the Irish coast flora, but separated from its main habitat by a temperature perhaps 4° C. lower in January than it will bear. These Boreal and Atlantic plants can only have spread to their isolated places in Norway in a climate some 3° C. warmer than the present. That this warmer time did occur in early post-glacial time is again proved by the stratification in the peats, where the plants most susceptible of cold (ash, oak, etc.) are found in the deepest layer or rather on the bottom itself—this also in places on the coast and in the mountains where now no forest tree grows.

These 3-4° C. recorded by the vegetation would certainly have raised the snow line, which now is 1200 to 1800 meters above the sea in Norway, above almost the whole epiglacial ice sheet, which nowhere attained 2000 meters. The great inland ice must then have become a dead glacier, and must have melted rapidly, especially from the margins. The last remnants of it might be supposed to have been situated near its maximum elevation, i.e., near the ice shed. This lay, as explained above, in deuteroglacial time at some distance to the southeast of the land watershed, as the many boulders in the upper eastern valleys which were transported upwards prove. The ice remnant is then to be