354 



OjST the contents oe a rock retreat 



clay might imply lack of hardness, hut the material has been metamorphosed by the 

 Conewago trap, which seems to be present in the flake, Fig. 3. This indurated clay 

 is black when fractured, and gray when weathered. 



Some of the knives figured exhibit great age, particularly the tra]) or dolerite, 

 Fig. 3. Of Figs. 6, 7, 8, the first has the sharpest lines, while they are least distinct 

 on Fig. S, representing probably one of the oldest of the specimens found, as it 

 occurred not only below the thirty inches of black mold, but below the surface of the 

 yellow clay. Occurring with cognate forms and material, and among the results of 

 human skill, its reference to the hand of man rests on a different basis from that of a 

 chance specimen from field or shore.- 



/• .^^tvui ''o ■ ^ji'U-' j' chapter ir. 



"■-■'•iH'*'" ■'' - " ■ CHISELS. PL. 2. 



What are here called chisels are also known as Celts — a term which should be 

 restricted to the people who bear this name. 



' Figure 1 represents a rude implement of gray sandstone, probably from the 

 mountains north of Harrisburg. Apparently shaped from a river pebble ; one end 

 has a straight edge suited for cutting, the other is obtuse and curved, adapted for 

 scraping, both ends coarsely shaped by hammering, and inefficient from the first, 

 unless spoiled by use. Greatest thickness about an inch, and the thickest specimen 

 of those figured. Hard enough to scratch glass. 



Fig. 5, a hard, fine-textured, pale, bluish, siHceous shale, flake-shaped by ham- 

 mering ; margined with a sharp but irregular edge. Less rude than Fig. 1 ; average 

 thickness about half an inch. 



■■- Fig. 6, a well-finished chisel of ruddy quartz; without polish, but the marks of 

 chipping scarcely apparent : edge in good condition ; sides sharp ; base truncate. It 

 has no indication of age, and I think it occurred about a foot from the surface. 



Figs. 2 and 7, apparently of Conewago dolerite ; each originally finished with a 

 rubbed or ground edge, which, with the entire surface, has become roughened and 

 gritty by long corrosion. In 2, the edge surfaces are slightly convex. 



Fig. 3, of indurite ; the rubbed or ground edge of its early state, and the entire 

 sni'face, have become harsh (but not gritty^) from corrosion, which has removed part 

 of the original surface, leaving fine veins and small nodules of a harder material to 

 project from the new surface. When similar objects occur in fields or along rivers, 

 the wear of the surface is attributable to friction and erosion ; hei'e, the action is not 

 mechanic but chemic. 



Fig. 4, sandstone; some evidence of the rubbed edge remains. 



