American archæologists have undoubtedly been repeatedly deceived by the misleading traces of comparatively modern remains in deposits of some geological antiquity; as in instances already referred to in the California gravel beds. In these, indeed, ground and polished instruments of stone, including a “plummet” of highly polished syenite, “an exhibition of the lapidary’s skill superior to anything yet furnished by the Stone age of either continent,”[56] are produced from time to time from the same post-pliocene formation where the remains of the elephant and mastodon abound. Dr. Abbott did not overlook the danger to which the archæologist is thus exposed on a continent which, so far as its aborigines are concerned, has scarcely yet emerged from its Stone age. He accordingly remarked in his original report: “The chance occurrence of single specimens of the ordinary forms of Indian relics, at depths somewhat greater than they have usually reached, even in constantly cultivated soils, induced me, several years since, to carefully examine the underlying gravels, to determine if the common surface-found stone implements of Indian origin were ever found therein, except in such manner as might easily be explained, as in the case of deep burials by the uprooting of large trees, whereby an implement lying on the surface, or immediately below it, might fall into the gravel beneath, and subsequently become buried several feet in depth; and lastly, by the action of the water, as where a spring, swollen by spring freshets, cuts for itself a new channel, and carrying away a large body of earth, leaves its larger pebbles, and possibly stone implements of late origin, upon the gravel of the new bed of the stream.” But there is little difficulty in separating chance-buried neolithic or modern implements from the genuine palæolithic celts or hatchets abundantly present in the undisturbed gravel beds, from which they have been taken on their first exposure.