1879.)  “ Turtle-Back” Celts in District of Columbia. 109 
found is about fifteen feet above low water mark. This sloping 
surface consists of fine sand, resting upon a layer of water-worn 
pebbles of stratified drift. The latter is a continuation of the 
formation known as the “cobble-stone”’ drift, upon which the 
eastern portion of the city of Washington is built. At several 
localities in that portion of the city, street cuts show exposures 
varying from five to forty feet in thickness. The several layers 
of worn and rounded boulders, “ cobble-stones,”’ gravel and sand, 
retain a perfect uniformity of stratification, showing their original 
deposition and arrangement through the action of water. Upon 
nearing the Branch we reach the shallow valley worn by that 
current, and the upper stratum of drift though much lower than 
farther back in the city, is not low enough to reach the level of 
that stream even at high tide. Examinations indicate, however, 
that the upper stratum on the north side of the stream, and the 
stratified gravel at the locality where the implements occur are 
the same, their continuity having been destroyed by the body of 
water just mentioned. 
The rude implements were found about one hundred and fifty 
yards from the edge of the water, associated with quite a variety 
of more modern manufacture, which, by the way, were, with the 
exception of two or three examples, all made either of white, 
vitreous, Or nearly transparent quartz. These represent spear- 
heads, arrow-heads and scrapers of great variety of sizes ; some 
of the latter consisting of split pebbles, nicely finished by chip- _ 
ping, leaving the convex side to retain nearly all of the original 
surface. Many of the arrow-heads have been manufactured in 
this way, by cleaving the pebbles and finishing up a few irregu- 
larities. The smallest specimens are represented by scrapers, 
probably used in smoothing down arrows; these are made of 
tabular pieces of semi-transparent quartz, about the size of a five 
cent nickel, shaped nearly like a horse-shoe, flat at base, and have 
the opposite convexity nicely beveled. 
The next class of implements represent manufacture of a ruder 
character, and undoubtedly points to greater age; to the earlier 
and lower state of the art of working stone for pointing weapons. 
These consist of quartz, and rarely chert, being rudely chipped 
and flaked, always leaving a greater irregular convexity upon one 
side of the specimen than upon the other, forming an intermediate 
grade between the modern forms and those tecmied, “ turtle- 
backs.” 
