PALEOLITHIC MAN IN AMERICA. 35 



the glacial period ; it is gorged in spring-time with ice-floes formed 

 within its own area and swept into it by its great affluent, as was 

 the ancient Delaware throughout a longer and more rigorous 

 winter ; and its bottom is a submerged terrace-plain of loam, sand, 

 and gravel differing from the Trenton gravel only in the less pro- 

 portion of ice-borne materials within it. In the shoal Susquehanna- 

 Chesapeake estuary grow a great variety of aquatic plants, har- 

 boring multitudes of minute animals, which together furnish 

 abundant food for fish and water-fowl, and just as it is now 

 among white men a far-famed fishing and hunting ground, so it 

 was a notable resort of the aborigines, as attested by the village 

 sites about its shores ; and since its shallow waters may be waded 

 over half its area and the simplest water-craft outlives the low 

 billows of its storms, the primitive spear-head and stone sinker 

 doubtless underlie the cartridge-shell and leaden sinker of the 

 present, just as the " turtle-back " of Trenton underlies the finely 

 chipped flint of the surface. During the later ice epoch of the 

 Quaternary the climate of the Delaware estuary was less tolerable 

 than that of the present Chesapeake estuary, but other conditions 

 were more favorable to concentration of piscine, avian, and human 

 life within and about it. There the river-breeding fishes were 

 stopped in their instinctive ascent toward former spawning- 

 grounds to increase their kind ; there the migratory birds must 

 have ended their vernal journey ings to nest and hatch ; there also 

 the flora, forced southward before the advancing ice, must have 

 grown mixed and varied; there the land fauna, pressed by the 

 northern cold and attracted by the forage and carnage, must have 

 lingered and multiplied ; and there primitive men must have con- 

 gregated and dominated over all. It is true but not surprising 

 that the fragile remains of fish, fowl, plants, or even human bones 

 have never been found in the porous and thoroughly leached 

 Trenton gravels, associated with the implements and the more 

 massive bones of mastodon, bison, and reindeer ; but the locality 

 was as distant from the ice-front as the arctic breeding-grounds of 

 to-day, and moderately mild climate is attested by the wonder- 

 fully abundant implements and the numerous population they 

 represent. 



The artificial origin of the "turtle-backs" has been ques- 

 tioned, and their abundance has been regarded as proof of their 

 natural origin ; and it is therefore not a work of supererogation 

 to point out that the Trenton gravels are largely wrought for 

 railway ballast, and have been scanned by the thousand tons by 

 eager workmen with the hope of reward before their eyes, and to 

 repeat that the argillite of which the implements are fashioned 

 rarely occurs in the deposit in the form of natural pebbles. Of 

 any hundred bits of argillite selected at random from the gravel- 



