Page:Popular Science Monthly Volume 4.djvu/674

654 Search for the sources of bowlders proves that large blocks on the southern flanks of the Jura Mountains must have been derived from Mont Blanc, sixty or eighty miles distant. Instead of passing down the Arne at Chamouni, the blocks proceeded northerly toward the Rhone, and thus across the great valley of Switzerland to the Jura. The magnitude of this ancient action equals much of the wonderful glacial phenomena of other districts in Europe, though hardly equal to what may be seen on this continent. But, being satisfied of the former enormous extension of the Alpine glaciers from examination of the striations and the dispersion of blocks, it is easy to generalize and refer similar phenomena in other countries, whose glaciers are extinct, to the same mighty cause.

In Scotland there may have been a centre of dispersion for glaciers from Ben Nevis, another in the south part of the province. In England, one in the Cumberland region; in Wales, one from Mount Snowdon. It is easy to discover the evidence of radial dispersion.

A combination of the glacial and iceberg agencies may be discerned in a map in Mr. Geikie's work, showing the courses of the striæ marked upon the rocks of Scandinavia. They diverge from the central water-shed between Norway and Sweden—part pushing toward. Iceland and Scotland, and part directed toward Lapland and the Baltic Sea. The distribution of the bowlders corresponds with these marks. Furthermore, these ice-masses seem to have come in contact with the water of the Baltic, and part have floated over Germany till high land obstructed farther movement, and a part may have been caught by the outflowing Baltic current, carried over the North Sea to the south part of England, and perhaps Iceland. At least, bowlders of Scandinavian origin are common in these regions, and have probably migrated in the way described. On the east shore of Scotland they are plenty; but, between these and those south of the Thames, none have been found, which fact has given rise to the theory of dispersion by means of icebergs through the Baltic.

In years past the prominent topic of discussion in scientific associations has been the character of the ice-movements in the Glacier period. One school has stoutly defended icebergs as the active agent, the other has vigorously insisted upon land glaciation. The example before us seems to require both these agents to account for all the phenomena of this period. Both classes seem to be right, though neither can explain all the facts. Nature's domain is so vast that human intellects do not seem to be capable of grasping the whole truth at once. We are like the mariners who seek to penetrate to the north-pole. They have penetrated a little way beyond Spitzbergen—they have gone nearer the goal through the straits west of Greenland, and have made great exertions in some other quarters. Each party has its theory of the character of the unknown region, as derived from a partial survey. By-and-by the whole of this area will be known, and it