This summary statement will convey some idea of the extraordinary
phase through which the earth passed in the early part of the
present geological era. But it must be added that a singular
circumstance prolonged the glacial regime in the northern
hemisphere. Modern geologists speak rather of a series of
successive ice-sheets than of one definite Ice-Age. Some, indeed,
speak of a series of Ice-Ages, but we need not discuss the verbal
question. It is now beyond question that the ice-sheet advanced
and retreated several times during the Glacial Epoch. The
American and some English geologists distinguished six
ice-sheets, with five intermediate periods of more temperate
climate. The German and many English and French geologists
distinguish four sheets and three interglacial epochs. The exact
number does not concern us, but the repeated spread of the ice is
a point of some importance. The various sheets differed
considerably in extent. The wide range of the ice which I have
described represents the greatest extension of the glaciation,
and probably corresponds to the second or third of the six
advances in Dr. Geikie's (and the American) classification.
Pages:
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445