s rewarded with another.[9] This
formation dates from far back in the Glacial period. If we accept Dr.
Croll's method of reckoning, we can hardly assign to it an antiquity
less than 150,000 years.

[Footnote 9: The chipped implements discovered by Messrs.
Abbott, Metz, and Cresson, and by Miss Babbitt, are all on
exhibition at the Peabody Museum in Cambridge, whither it is
necessary to go if one would get a comprehensive view of the
relics of interglacial man in North America. The collection of
implements made by Dr. Abbott includes much more than the
palaeoliths already referred to. It is one of the most important
collections in the world, and is worth a long journey to see.
Containing more than 20,000 implements, all found within a very
limited area in New Jersey, "as now arranged, the collection
exhibits at one and the same time the sequence of peoples and
phases of development in the valley of the Delaware, from
palaeolithic man, through the intermediate period, to the recent
Indians, and the relative numerical proportion of the many
forms of their implements, each in its time.... It is doubtful
whether any similar collection exists from which a student can
gather so much information at sight as in this, where the
natural pebbles from the gravel begin the series, and the
beautifully chipped points of chert, jasper, and quartz
terminate it in one direction, and the polished celts and
grooved stone axes in the other." There are three principal
groups,--first, the interglacial palaeoliths, secondly, the
argillite points and flakes, and thirdly, the arrow-heads,
knives, mortars and pestles, axes and hoes, ornamental stones,
etc., of Indians of the recent period. Dr. Abbott's _Primitive
Industry_, published in 1881, is a useful manual for studying
this collection; and an account of his discoveries in the
glacial gravels is given in _Reports of the Peabody Museum_,
vol. ii. pp. 30-48, 225-258; see also vol. iii. p. 492. A
succinct and judicious account of the whole subject is given by
H. W. Haynes, "The Prehistoric Archaeology of North America," in
Winsor's _Narrative and Critical History_, vol. i. pp.
329-368.]

[Sidenote: The