Here we have the
possibility of an explanation of the advances and retreats of the
glaciers. The refrigerating agencies would proceed until an
enormous burden of ice was laid on the land of the northern
hemisphere. The land apparently sank under the burden, the ice
and snow melted at the lower level and there was a temperate
interglacial period. But the land, relieved of its burden, rose
once more, the exposed surface absorbed further quantities of
carbon, and a fresh period of refrigeration opened. This
oscillation might continue until the two sets of opposing forces
were adjusted, and the crust reached a condition of comparative
stability.
Finally, and this is the more serious difficulty, it is said that
we cannot in this way explain the localisation of the glacial
sheets. Why should Europe and North America in particular suffer
so markedly from a general thinning of the atmosphere? The
simplest answer is to suggest that they especially shared the
rise of the land. Geology is not in a position either to prove or
disprove this, and it remains only a speculative interpretation
of the fact We know at least that there was a great uprise of
land in Europe and North America in the Pliocene and Pleistocene
and may leave the precise determination of the point to a later
age.
Pages:
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453