Drift Period
the period during which the drift described above was deit should not have recurred time after posited. Though there is no reason why time during bygone geological ages, yet the term "drift-period" as a measure of duration is limited to the time commencing during the Newer Pliocene or Pleistocene, and terminating with the Post Pliocene or Post Pleistocene, during which drift was deposited in the latitudes in which we find it now. That it is essentially a glacial phenomenon is apparent from the fact that while becoming more marked in its character on this side the equator, the farther N. one goes, it dies out about lat. 50° N. in Europe and 40° in North America. Hence it is often called Northern Drift. A corresponding development of it, however, exists in the S. hemisphere. This becomes more marked as one approaches the S. pole, and disappears, between 40° and 50° S. lat. Where it exists nearer the equator it is deposited around some giant mountain, the scratches and striations on the boulders and pebbles radiating from the mountain on every side. The drift is now universally attributed, as Agassiz long ago suggested, to the action of ice, the only controversy remaining being whether land ice or floating icebergs took the chief part in its distribution. Hence it is often called, as by Sir Charles Lyell, Glacial Drift.