Page:The Journal of geology (IA journalofgeology21894univers).pdf/142
greater specific gravity in a great degree replaced the melting ice margin, the consequence appears to have been that the land finally lost in height perhaps as much as 200 to 400 meters. We shall find analogous phenomena in other glaciated countries.
The thickness of the inland ice in Norway at this time we are able to estimate by the upper limit of foreign boulders and by the lower limit of the rocks on mountain summits which were not reached by the ice sheet. Where a great continuous scoring ice sheet has worked we find in Norway, as in Greenland and elsewhere, the smooth undulating surface lines with fresh rock surfaces. Higher up, above the reach of ice, we find the nunatak formation with peaks and cirques (botner) and with highly weathered rocks and mighty talus and other debris. By such limits we can approximately determine that the maximum height of the ice sheet in southern Norway was below 2000 meters, in northern Norway about 1200 to 1500 meters, these being reckoned from the present sea level. As the mean height of the Norwegian highland may be estimated at 800 to 1000 meters, and as only central Norway reaches more than 1200 meters, we get an ice sheet which, near its axis, will measure only about 800 to 1000 meters. To this thickness of the ice the depression of the land answers very well according to O. Fisher's theory.
The first great Quaternary glaciation of Norway was followed by other great climatic changes. To get a more handy terminology than the common periphrastic nomenclature, I have proposed, for the most pronounced periods, the names proteroglacial for the earlier great ice age as distinguished from the well-known last great glaciation that followed—the deuteroglacial. I have chosen and press for acceptance at the Congress terms implying the first and the second of two periods because these two glaciations seem to be demonstrable for all glaciated countries. The names cannot well be misunderstood, and if, perchance, as some American and German geologists assume, a third separate glaciation can be proved, it will be easy to give it a name apart. So far we can only distinguish in Norway preglacial, proteroglacial,