A STUDY OF PREHISTORIC ANTHROPOLOGY. 



633 



This implemeut* was made from a pebble which has been split in two 

 The upper or flat surface shows the chips 

 with the bulb of percussion by which it was 

 worked. A portion of the rolled surface of 

 the pebble is left untouched, and shows in the 

 cut, proving beyond doubt its intentional and 

 consequently human manufacture. It is im- 

 possible that these fractures should have 

 been either natural or accidental. This ex- 

 hibition of the rolled surface, the crust of the 

 pebble, is a peculiarity belonging chiefly to 

 the valley of the Potomac, where they have 

 been found in considerable numbers. I have 

 ventured to name this the Washington imple- 

 ment, in contradistinction from that other 

 kind which is chipped all over, shows no 

 trace of the crust of the pebble, and which 

 Dr. Abbott once named "Turtle back," but 

 is now by his consent changed to " Trenton implement." 



Fig. 5. 

 Yellowish-beown Quartzite. 



(Pamunkey, Charles County, Maryland. Col- 

 lected by O. N. Bryan. ) 



Fig. 6. 

 Indurated Clay Slate. 



(Pamunkey, Charles County, Maryland. Col- 

 lected by O. N. Bryan. ) 



Fig. 7. 

 Reddish Quartzite. 



(Georgetown. District of Columbia. 

 Collected by James Webster. ) 



See Fig. 5. 



