1879:]  “ Turtle-Back” Celts in District of Columbia. III 
tion reaches its extreme elevation less than half an inch back of 
this, forming an angle of 64° when viewed from either side. 
Toward the base the descent is more gradual, where there are 
deeper notches than usually occur, the projections on either side 
somewhat worn, showing traces of having been used. From all 
appearance such an implement, as nearly all of this type, appears 
useless in attempting to penetrate the skin of anything more 
resisting than that of fishes. 
It is very probable that these rude implements were not manu- 
factured and employed by the Indians of historic times who 
inhabited this region. The question is asked, Why then do these 
implements occur with more modern ones upon the surface, or in 
washes? The only reason that can be given is, that the rude 
forms occupying that portion of the stratum of sand resting upon 
the gravel, and those of modern manufacture occupying the sur- 
face of the later deposit of earth and sand, were brought together 
by the removal of the intervening siliceous matter through the 
prolonged and repeated agency of rains. Thus the surface relics 
were gradually let down, as it were, as the sand and earth were 
washed away. This may appear unsatisfactory, but the suggestion 
is based upon the following reasons: first, that the sand being 
fine and easily removed by water (through the agency of rains) 
falling over this locality and over the bluffs, follows the most 
natural course towards the stream, taking with it the light silicious 
particles, and washing them away from the pebbles, stones and 
implements, allowing them to be deposited in an indiscriminate 
mixture in the little water courses and ravines; second, that this 
has been the case is apparent from the fact of its occurrence in 
several places at this time; also that small embankments and 
hillocks occur, consisting of gravel thus deposited or brought 
together by the removal of the lighter soil ; and at this day, after 
any continued or hard rains, numerous accumulations of pebbles, 
amongst which we find implements, are formed by the removal 
of earth and sand by the temporary streams. 
In this way the surface remains have not been carried away 
from the localities upon which they had rested, but, were gradu- 
ally dropped to a lower horizon, until after a time they reached 
the stratum containing the rude and more ancient varieties. 
In this connection I shall speak of several localities in Penn- — 
sylvania, one of which occupies a position in the eastern portion 
