246 



MAN AND THE GLACIAL PERIOD. 



the only material in the vicinity capable of being chipped, 

 prehistoric men of that vicinity were compelled to make a 



Fig. 66.— Section of the Trenton gravel in which the implements described in 

 the text are found. The shelf on which the man stands is made in process 

 of excavation. The gravel is the same above and below (photograph by 

 Abbott). 



virtue of necessity and use the inferior material. Of all 

 the implements found by Dr. Abbott in the gravel, only 

 one was flint ; while upon the surface innumerable arrow- 

 heads of flint have been found. The transition, also, in 

 the type of implements is as sudden as that in the kind of 

 material of which they are made. Below the superficial 

 deposit of black soil, extending down to the depth of about 

 one foot, the modern Indian flint implements entirely 



